Mayday (2013) s18e08 Episode Script
Deadly Inclination
First Officer de Fraia: Go around.
Captain Liberti: Hold the glide.
Narrator: Near Zurich Airport, a DC-9 plows into the ground six miles short of the runway.
Russell Lawton: It was a fatal loss of life.
It was a tragedy.
Ulrich Braun: You have impressions and smells that you never forget.
It changes you.
Hans-Peter Graf: Pitch and roll, fine.
Flaps, good.
No stabilization problems.
Narrator: Close analysis of the evidence only deepens the mystery.
Hans-Peter Graf: It was definitely flying too low but why, we didn't know.
Robert Benzon: Maybe it was something we can't see.
Narrator: Could a hidden fault deep inside the airplane have led the two pilots down a deadly path? Robert Benzon: That put all the other aircraft in the sky in danger.
Captain Liberti: Zurich, good evening.
Alitalia 4-0-4, descending one-zero-zero.
Echo received.
Air Traffic Controller: Alitalia 4-0-4, Zurich arrival.
Good evening.
Narrator: The crew of Alitalia flight 404 is nearing the end of an evening flight to Zurich, Switzerland.
Air Traffic Controller: Alitalia 4-0-4, fly heading three-two-five radar vectors to ILS fourteen.
Captain Liberti: Radar vectors to runway one-four on heading three-two-five.
Captain Raffaele Liberti is a senior Alitalia pilot with more than twenty years' experience.
First Officer de Fraia: How much is the visibility? Captain Liberti: Visibility is nine kilometers.
Narrator: First Officer Massimo de Fraia is the pilot flying the plane tonight.
He's new to the airline, having joined just last year.
Franco Bergante also flew for Alitalia in the 1990s.
Franco Bergante: At the time, it was one of the safest companies and best trained in the world.
I knew the captain very well, the co-pilot a little less.
Narrator: There are four flight attendants and forty passengers in the cabin.
Passenger: Thank you.
Narrator: Several of the passengers are Swiss industrial workers heading home after a lengthy stretch of work.
Passenger: Oh it'll be nice to get back, huh, after all this time away? Let's hope they recognize us.
Hans-Peter Graf: Typically the passengers were employees going back and forth, uh, from Switzerland to Italy, especially to Milan.
Narrator: The plane is a McDonnell Douglas DC-9 that's been flying since 1974.
Todd Curtis: The DC-9 was one of the mainstays of the industry from the 1960s through the 2000s.
It was very, very popular in the U.
S, Western Europe and around the world, primarily for shorter regional trips.
Franco Bergante: Even if it wasn't among the more modern planes, it was a good airplane.
Narrator: Flight 404 left Milan's Linate Airport twenty-five minutes ago.
The flight path takes it almost directly north over the Alps to Zurich's Kloten Airport.
Air Traffic Controller: Lufthansa 1-8-7-3, maintain two-four-zero.
Narrator: At Zurich air traffic control, it's a busy evening.
Air Traffic Controller: Swiss 3-6-1-1, maintain two-three-zero.
Narrator: The airport is one of Europe's main hubs, serving 12 million passengers a year.
Air Traffic Controller: Alitalia 4-0-4, turn right heading three-four-zero.
Captain Liberti: Right three-four-zero, Alitalia 4-0-4.
Narrator: Alitalia 404 is lining up for its approach to the airport.
Captain Liberti: You should slow down a bit.
The faster you go, the less time you have for landing.
Air Traffic Controller: Alitalia 4-0-4, reduce to two-one-zero knots.
Captain Liberti: Two-one-zero knots reducing, 4-0-4.
You see? Narrator: The pilots are preparing for what's called an ILS or instrument landing system approach.
Todd Curtis: An instrument landing system is a series of technologies, primarily radio transmitters on the ground, that allows an aircraft to align itself both vertically and horizontally with the runway.
Air Traffic Controller: Alitalia 4-0-4, reduce to one-eight-zero knots.
Captain Liberti: Reducing one-eight-zero, 4-0-4.
Do you have the glide slope? First Officer de Fraia: Uh, it's on one Captain Liberti: Let's do it on one.
Narrator: The crew sets the navigation instruments to pick up the ILS signal from the runway.
First Officer de Fraia: Radio one confirmed.
Todd Curtis: There is a set of signals, which goes out at an angle from the ground that gives them an idea of the glide slope, which is typically around a three degree slope.
Robert Benzon: It gives you one tiny pencil thin beam that you can fly down that ensures that you're going to stay above the trees and not hit anything below there and it'll, it'll lead you right to the end of the runway.
Air Traffic Controller: Alitalia 4-0-4, reduce to one-six-zero knots.
Captain Liberti: Reducing one-six-zero.
Captured LOC.
Captured glide path so we're on the beam.
Narrator: Flight 404 is third in line on approach, the runway 12 miles straight ahead.
The pilots can't see it yet, but their navigation instruments show they are locked on to the proper signals.
All they need to do now to finalize the approach is intercept a radio beacon known as the outer marker.
Hans-Peter Graf: The outer marker is something like the last occasion to check whether the ILS is correct.
Todd Curtis: That tells them as they get closer that they're still right on the money.
First Officer de Fraia: Flaps 25.
Captain Liberti: Flaps 25.
The outer marker check is at 1,250 feet, almost four miles.
First Officer de Fraia: Didn't we pass it? Didn't we pass the outer marker? Captain Liberti: No.
No, it hasn't changed yet.
Air Traffic Controller: Alitalia 4-0-4, speed as convenient.
Contact tower one-one-eight-point-one.
Captain Liberti: One-one-eight-point-one, good-bye.
First Officer de Fraia: That doesn't make sense to me.
Narrator: The runway should be just ahead.
But the first officer still can't see it.
Something's not right.
First Officer de Fraia: Go around.
Captain Liberti: No, no, no, no.
Hold the glide.
Can you hold it? First Officer de Fraia: Yes, sir.
Captain Liberti: Ah! Air Traffic Controller: Lufthansa 1-0-3-4, reduce to one-six-zero knots.
Alitalia 4-0-4.
Narrator: The controller has no idea why Alitalia 404 has suddenly disappeared from radar.
Rabbit 932 Pilot: Rabbit 9-3-2, established ILS 14.
Air Traffic Controller: Rabbit 9-3-2, do you see an aircraft ahead of you? Rabbit 932 Pilot: Standby.
No traffic in sight but there's fire on the ground.
Air Traffic Controller: Roger.
Narrator: It can only mean one thing.
Air Traffic Controller: This is air traffic control.
We have an emergency.
Narrator: Swiss and German firefighters rush to the site of the crash of Alitalia flight 404, a forested hillside six miles from Zurich's Kloten Airport.
Ulrich Braun: At first, you could see a glow in the woods and there was a taste of burning rubber and when we could finally see the actual crash site it was horrific.
(SPEAKING FOREIGN LANGUAGE) Narrator: The plane has cut a swathe through the trees, scorching the surrounding area.
The scale of the destruction is staggering.
Ulrich Braun: The airplane was completely destroyed.
The main goal was to save people.
Narrator: But as fire crews suppress the flames and comb through charred debris, they can find no one to save.
All forty-six people aboard the flight are dead.
Franco Bergante: I was very upset because it was a loss of someone close.
Ulrich Braun: You have images that you have to deal with.
You have impressions and smells that you never forget.
It changes you.
Narrator: With the wreckage still smoldering, an investigation into what happened is already underway.
Hans-Peter Graf is with Switzerland's Air Accident Investigation Bureau, or AAIB.
Hans-Peter Graf: The first thought is: Well, bad news.
It's gonna be a big and long investigation.
I had to get a first impression of what had actually happened that night.
So I went straight to air traffic control center in Zurich.
Hans-Peter Graf: Hello.
Good evening.
Air Traffic Controller: Good evening.
Narrator: Graf meets with the last person to speak to the Alitalia crew.
Hans-Peter Graf: What can you tell me about flight 404? Hans-Peter Graf: I hoped to learn if the crew had issued an emergency beforehand, if there was anything unusual about the airplane.
Air Traffic Controller: It was routine.
Uh they were making an ILS approach, as usual.
They never reported any problems.
Hans-Peter Graf: Can you replay the radar track? Air Traffic Controller: Yes, of course.
Narrator: Graf knows that most control centers keep recordings of all recent radar tracks.
Hans-Peter Graf: I had a closer look at the radar screen itself.
I saw the airplane symbol AZ 404 together with the altitude reading on the screen.
Hans-Peter Graf: Well, they may not have reported a problem, but they sure had one.
Look at that glide slope.
Graf discovers that more than five minutes before the crash, flight 404 was already too low and descending lower.
Hans-Peter Graf: I noticed that the airplane was flying 1,200 feet below the actual flight path.
Narrator: The proper glide slope would have taken the DC-9 on a gradual descent right to the foot of the runway.
Instead, the plane flew an almost parallel path more than a thousand feet lower right into the side of a small mountain.
Hans-Peter Graf: You didn't notice their altitude? Air Traffic Controller: Well, I was juggling six flights.
All the 404 calls were normal.
They said they were on glide.
Todd Curtis: That particular controller would assume if they were reporting they were lined up with the runway and that they were on the glide path that they were safely above any terrain.
Hans-Peter Graf: And your minimum safe altitude warning system didn't sound? Air Traffic Controller: We don't have one installed as of yet.
Russell Lawton: Unfortunately at the time, you know, they didn't have the minimum safe altitude warning system in place in Zurich.
In the U.
S, it had already been in place for ten years.
Hans-Peter Graf: You said they were doing an ILS approach.
Air Traffic Controller: Mm hmm.
Hans-Peter Graf: Then we don't have a choice.
Shut the system down immediately.
We can't risk another flight.
Narrator: Graf worries the runway guidance system may be malfunctioning.
A full test of the system will cause major disruptions for Zurich Airport, but it has to be done.
Robert Benzon: If the ground transmitter was malfunctioning, that put all the other aircraft in the sky in danger.
So they have to shut it down until they, they have it checked out by electronic technicians.
Narrator: It could take a day or more to get results, but if the testing reveals a fault with the ILS it could explain why Alitalia flight 404 ended in tragedy.
Daylight reveals a 300-meter long scar through a hillside forest northwest of Zurich where Alitalia 404 crashed hours earlier.
Joining the investigation is Bob Benzon of the US National Transportation Safety Board.
Robert Benzon: Because the aircraft was manufactured in the United States, our role was really to assist the Swiss government in determining what happened.
Robert Benzon: That's a lot of fire damage.
It's gonna make ID'ing parts a real chore.
Robert Benzon: The thing that stuck out was the amount of destruction.
The only truly recognizable things were the engines and the landing gear.
But the rest of it was pretty well burnt up.
Robert Benzon: Let's see that map again.
Narrator: Investigators wonder what the mangled terrain can tell them about the plane's last moments.
Robert Benzon: It looked to us like the aircraft had, had struck the trees in a bit of a level attitude, although parts of the right wing had, had been sheared off by the trees and that caused a more lift to occur on the left side of the aircraft, causing the aircraft to roll.
So the eventual impact was nearly inverted.
(PHONE RINGING) Robert Benzon: Hello.
Benzon.
Benzon gets word on Zurich Airport's instrument landing system.
Robert Benzon: That's for certain? Okay.
Narrator: Overnight testing has revealed that the guidance technology is in perfect working order.
Captain Liberti: Captured LOC.
Captured glide path, so we're on the beam.
Narrator: It means the ILS was sending the proper signal throughout flight 404's descent to the airport.
Robert Benzon: The ILS is fine.
So whatever brought that plane down, the evidence has gotta be here somewhere.
Robert Benzon: That led us to believe that perhaps there was a problem onboard the aircraft rather than on the ground.
Narrator: More answers about the mysterious crash may be close at hand.
The team has recovered both of the plane's black boxes.
But they won't know if the data they need has survived the crash until they get the recorders to a lab for analysis.
Hans-Peter Graf: So they were cleared for runway 14.
It looks like they're on the right heading.
They're way too low.
It's like they don't even know the hill's there.
I wonder how well the pilots knew the route.
Narrator: Searching for answers, investigators look into the pilots' work records.
They discover that besides being a senior Alitalia pilot, the captain was also a former military airman.
Robert Benzon: We learned that the captain had over 10,000 flying hours.
Captain Liberti: Zurich, good evening.
Alitalia 404, descending one-zero-zero, echo received.
What's more, the Milan to Zurich route was nothing new to him.
Hans-Peter Graf: The captain, who was flying this route many times in his career, was very familiar with it.
Narrator: They learn that the 28-year-old first officer was far less experienced.
But his record is spotless, and he'd also landed at Zurich before.
Robert Benzon: Both pilots had flown this route many times before in the same cockpit sometimes.
So they were familiar with what the approach should look like.
Narrator: Across Zurich and throughout Europe, news of the crash has left people rattled.
The quiet city, best known for its banking sector, hasn't seen a major air disaster in almost 20 years.
Russell Lawton: It was such a tragedy.
It was an all-fatal loss of life and so it was reported in the media extensively.
Narrator: The media attention puts mounting pressure on investigators.
Hans-Peter Graf: Is this the flight data? Narrator: Finally, they have some good news.
Information from both the flight data recorder and the cockpit voice recorder has survived.
Hans-Peter Graf: We should get this up on the projector.
Narrator: But will it provide the answers investigators need? Russell Lawton: Was there an aircraft malfunction of some sort? An instrument failure? A flight crew problem? Those are the immediate things that you zero in on.
Robert Benzon: Well, there's not a lot of parameters but it should tell us something.
Narrator: Investigators begin with the flight data, looking for any sign of a mechanical problem onboard.
Hans-Peter Graf: Thrust is good.
Robert Benzon: Although the thing was reasonably ancient compared to the modern ones, it only had 10 parameters, two of those parameters were engine pressure ratio, which means how much thrust the engines were putting out.
And they showed us that the engines were operating normally up until the time of impact.
Hans-Peter Graf: Pitch and roll, fine.
Flaps, good.
Robert Benzon: Yup.
Hans-Peter Graf: No stabilization problems.
Everything seems normal from a mechanical standpoint.
Robert Benzon: Even the glide is smooth and straight.
It's just all over a thousand feet too low.
I don't get it.
Narrator: The data doesn't reveal any mechanical failure that can explain the crash.
It only confirms the mysterious glide path recorded by air traffic control radar.
Hans-Peter Graf: On the FDR data, we could not find any technical issues at all.
The airplane performed as per design.
It was definitely flying too low, but why, we didn't know.
Hans-Peter Graf: Please set up the playback machine.
We need to hear what was going on in that cockpit.
Trying to understand why a well-trained Alitalia crew flew their DC-9 into the ground miles short of the runway, investigators now turn to the cockpit recording.
Robert Benzon: Something was going wrong with the perceptions of the crew, perhaps the aircraft itself, to cause it to be almost a thousand feet, maybe a little bit more, below where it should have been on the approach.
So that became a focus.
Captain Liberti: (Static) But as soon as they start listening to the recording, they know they have a problem.
Hans-Peter Graf: There was a lot of, of noise and, uh, it was first of all difficult to understand.
Hans-Peter Graf: It sounds like they weren't using their headsets for some reason.
Captain Liberti: You should slow down a bit.
Robert Benzon: The flight crew weren't using boom microphones.
They were just talking into one single microphone located in the middle of the instrument panel.
Captain Liberti: The faster you go, the less time you have for landing.
Todd Curtis: So this led to some of the words not being understood by the accident investigators.
Hans-Peter Graf: Send it back to the lab.
We won't be able to get anything off this.
Narrator: It's a disappointing setback.
Investigators can only hope lab technicians can find a way to filter out the noise and produce an audible recording.
Robert Benzon: So it was very difficult for the investigators to create a true transcript.
Narrator: In a facility at Zurich airport, investigators survey wreckage recovered from Alitalia flight 404.
They're looking for any clue that might help explain why the DC-9 flew for more than five minutes on a fatally low glide path before plowing into a hillside.
Robert Benzon: I'm surprised there are planes that still have this altimeter.
They're ancient.
What if they misread their altitude? Narrator: The DC-9's cockpit was equipped with what's known as a drum pointer altimeter.
Hans-Peter Graf: The drum pointer altimeter is known to be prone to be misread.
Robert Benzon: You have to look at the drum, and then you have to look at the needle.
And it's almost like an analogue watch versus a digital watch.
Narrator: Unlike a modern digital altimeter, the drum pointer design can only be read in two steps.
Feet in thousands is indicated on a drum like an odometer in a car.
Feet in hundreds is indicated by a pointer that moves around a scale like a clock face.
The problem with the design is as it moves the pointer can sometimes obstruct the pilots' view of the numbers on the drum.
Todd Curtis: If that needle happened to be obscuring part of the odometer that showed the thousands of feet, there could be some confusion as to whether it was one particular altitude or maybe a thousand feet away from that, so the potential for confusion existed.
Narrator: The industry has been phasing out the notoriously confusing instrument for years, but it's still found on older planes like DC-9s from the mid-70s.
At this stage in the investigation, the team has no way of knowing if the pilots misread the instrument.
Robert Benzon: If they did misread it, that could explain why they were so low on approach.
But the GPWS would have warned them.
The ground proximity warning system, or GPWS, is an onboard technology designed to help pilots avoid terrain.
The system bounces radio waves off the ground below to measure altitude and sounds a cockpit warning if the plane gets too low.
Robert Benzon: And there's no mistaking that alarm.
Narrator: Investigators know the Alitalia DC-9 was equipped with a GPWS, but did the pilots get a warning before the fatal impact? Robert Benzon: We really need that CVR.
Robert Benzon: Hey.
Hans-Peter Graf: Hey.
Robert Benzon: All right.
This is the proper glide slope for runway 14.
Hans-Peter Graf: Right.
I've got the transcript for the enhanced recording.
Narrator: They hope to finally get some answers from the cockpit recording, now cleaned up by audio technicians and ready for playback.
Todd Curtis: The picture that was given by the full transcript is more than enough to get a very good idea of what the sequence of events was in the cockpit.
Hans-Peter Graf: Okay.
First Officer de Fraia: Then we do a radio approach? Captain Liberti: Yes.
Hans-Peter Graf: They're at just over 4,000 feet here, which is well below the glide slope.
Robert Benzon: Okay, so but they need to level off to capture the glide but they kept descending.
First Officer de Fraia: On one Captain Liberti: Let's do it on one.
First Officer de Fraia: Radio one confirmed.
Hans-Peter Graf: It sounds like they're just on radio one.
Narrator: ILS transmitters send radio signals to two navigational receivers in the cockpit, Nav Radio 1 and Nav Radio 2.
The pilots can use either one to guide the plane.
Investigators now know the crew selected Nav Radio 1.
But they're still hoping to discover something about the unusual low glide slope and about the GPWS.
Air Traffic Controller: Alitalia 404, reduce to one-six-zero knots.
Captain Liberti: Reducing one-six-zero.
Captured glide path so we're on the beam.
Robert Benzon: Stop it there.
On the beam? They're well below the glide slope there.
Hans-Peter Graf: They are more than 1000 feet below it.
Robert Benzon: So why is the captain saying then that he captured it? What they're hearing from the cockpit only deepens the mystery.
Investigators know that right in front of both pilots is an instrument that should be showing their exact glide slope position.
It's called a glide slope indicator.
Todd Curtis: There are visual cues, specific systems that are in place that give a pilot an idea of whether or not they're too high or too low on the glide slope.
Robert Benzon: Did they misread the altimeter and the glide slope? I mean that doesn't seem possible.
Hans-Peter Graf: Let's keep listening for the GPWS.
Robert Benzon: Okay.
First Officer de Fraia: Flaps 25.
Captain Liberti: Flaps 25.
The outer marker check is at 1,250 feet, almost four miles.
First Officer de Fraia: Didn't we pass it? Didn't we pass the outer marker? Captain Liberti: No.
No, it hasn't changed yet.
Hans-Peter Graf: Something in that cockpit is confusing these pilots.
Air Traffic Controller: Alitalia 404, speed as convenient, contact tower one-one-eight-point-one.
Captain Liberti: One-one-eight-point-one, goodbye.
First Officer de Fraia: That doesn't make sense to me.
Go around.
Captain Liberti: No, no, no.
Hold the glide.
Robert Benzon: The CVR had the first officer attempting to go around and then being countermanded by the captain.
There was a lot of confusion there.
- Captain Liberti: Can you hold it? - First Officer de Fraia: Yes, sir.
Captain Liberti: Ah! Narrator: Investigators are stunned both by what they've heard and by what they haven't heard.
Hans-Peter Graf: No ground proximity warnings at all.
Robert Benzon: The fact that the aircrew didn't get a warning from the ground proximity warning system, uh, was a surprise to us.
Robert Benzon: And the captain called off a go around.
They now face more questions than ever.
How could two professional pilots both misread their glide slope indicators? Why did the plane's ground proximity warning not sound? First Officer de Fraia: Go around.
Captain Liberti: No, no, no, no.
And why did the captain call off the one maneuver that might have saved his plane and his passengers? Robert Benzon: This one looks pretty beat up too.
Investigators examine a pair of flight instruments recovered from the cockpit of Alitalia 404 - the heading indicators, known as HSIs.
They hope the damaged instruments can confirm whether or not the pilots misread their glide slope on approach to Zurich.
Hans-Peter Graf: They recovered the HSI from the wreckage, and we wanted to know what was the indication of the glide slope.
Robert Benzon: Okay, so that mark there, is that the same as on the first one? Narrator: They closely examine a small arrow on the glide slope indicator situated on the right side of each HSI.
It's the instrument that tells the pilots if they're flying too high or too low.
Robert Benzon: We found what we call slap marks, which means the indicator as it was being destroyed, uh, the needles on the indicator slapped against the background.
So at the time of impact you could determine what that instrument was showing you.
Todd Curtis: It did have markings on it showing that they were on glide slope.
Robert Benzon: So they were both indicating on glide.
Narrator: It's a major discovery.
It means that both indicators were on the glide slope and the pilots didn't misread them.
Captain Liberti: Captured LOC.
Captured glide path so we're on the beam.
Narrator: The captain announced capture because his instrument was showing him he was on the proper descent path even though he was actually more than a thousand feet below it.
Franco Bergante: They got what's called a false glide slope.
Robert Benzon: And that kind of led us to wonder how that could occur.
The team now needs to understand why critical cockpit instruments were displaying the wrong glide slope.
With help from Alitalia, they begin examining the onboard source of that information, the number one navigation receiver.
Did the unit have some kind of defect that caused it to send a faulty signal? Hans-Peter Graf: I couldn't understand why can the autopilot fly a faulty glide path, why the pilots don't get warned about that.
There must be something totally wrong with this receiver.
Robert Benzon: I don't see any corrosion.
All the internal components seem to be in the right place.
No obvious defects.
Maybe it's something that we can't see like a short-circuit.
Robert Benzon: Well, we had a very good idea that the Nav 1 receiver was, was putting out false information.
But we couldn't directly test it because of damage to the device during the accident sequence.
So the Swiss investigators decided to do some testing.
Narrator: Investigators start by deliberately shorting-out a Nav 1 receiver and then testing it in a flight simulator to see what happens.
Hans-Peter Graf: Okay.
It should be in the menu.
I pre-programmed the route as 404 approach.
Russell Lawton: Simulation tests are important during an accident investigation because what you're trying to do is recreate the scenario and circumstances that led up to the accident.
Then they simulate the flight path of Alitalia 404.
Hans-Peter Graf: We're 15 miles out, 1200 feet below glide.
Stand by.
Narrator: Graf wants to see if he can reproduce the same false glide path that deceived the Alitalia crew.
Hans-Peter Graf: Switch to Radio 1.
There it is! Narrator: A false glide indication on the display.
Hans-Peter Graf: And no warning flags.
Narrator: Graf is stunned to see that the short-circuited receiver defaults to the on-glide position and that there's no warning about the malfunction.
Todd Curtis: Typically if the signals are not correct there's some sort of warning given in the instrument itself.
There was no warning.
Hans-Peter Graf: I was really surprised that somebody could design a piece of equipment without warning the pilots if there is something wrong with it.
Robert Benzon: It was a, uh, kind of an aha moment.
Captain Liberti: Captured LOC.
Captured glide path so we're on the beam.
Narrator: There was now no doubt that a short-circuit in the Nav 1 receiver caused the deadly glide slope display malfunction.
Did it also somehow disable the potentially lifesaving ground proximity warning? Hans-Peter Graf: Keep going.
Narrator: That's what Graf wants to know next.
Hans-Peter Graf: Thirty seconds from impact.
The simulation soon gives him an answer.
Hans-Peter Graf: Nothing.
It should have sounded by now.
The plane's GPWS never sounds a warning.
Robert Benzon: And it turns out that if the navigation radios aren't putting out a good signal to the rest of the aircraft, the GPWS it just doesn't work.
Narrator: The GPWS finding leads to another disturbing question.
First Officer de Fraia: That doesn't make sense to me.
Narrator: Would the crew have been able to save their plane and 40 passengers First Officer de Fraia: Go around! Captain Liberti: No, no, no, no.
Hold the glide.
Narrator: if the captain had initiated a go around when his first officer called for it? Hans-Peter Graf: Okay, so no hesitation when I give the order, okay? We're almost there.
Five, four, three, two, one.
Go around.
Climbing safely.
Those poor bastards.
Hans-Peter Graf: Had the captain not intervened they would have made it.
Robert Benzon: The aircraft would have passed over the top of the mountain without striking it.
Not, not by much, you know, a couple hundred feet perhaps.
Narrator: It's a heartbreaking discovery, one that motivates investigators to try to understand why the fatal decision was made.
Why did a seasoned pilot overrule his first officer and miss his last chance to avoid disaster? Hans-Peter Graf: Let's take it from earlier in the flight.
Narrator: For more insight into what the captain may have been thinking, they return to the cockpit voice recording.
First Officer de Fraia: How is it approaching? Captain Liberti: Approaching, turning left to Schaffhausen.
Narrator: They listen from earlier in the approach to try to get a sense of how well the pilots were working together.
Captain Liberti: I told you not to go on that beacon.
Robert Benzon: Well, it was a crew that had a very experienced fellow in the left seat and a very inexperienced fellow in the right seat, and that always causes a bit, a bit of consternation at times during a flight.
Captain Liberti: Go to the left.
You see? You'd moved.
What emerges is troubling.
The captain seems constantly dissatisfied with his first officer.
Captain Liberti: It's compulsory to go there.
Todd Curtis: There seemed to be some sort of a mentor/student relationship, the first officer being admonished at some points by the captain.
Captain Liberti: You should slow down a bit.
The faster you go the less time you have for landing.
Air Traffic Controller: Alitalia 404, reduce to two-one-zero knots.
Captain Liberti: Two-one-zero knots reducing, 404.
You see? Hans-Peter Graf: My impression is that the captain didn't trust the co-pilot's abilities because he, he already showed that he wasn't very sure what he was doing.
Robert Benzon: Not exactly an ideal working relationship.
Franco Bergante: The captain was a bit tough.
And the co-pilot was a bit weak.
So let's say that the absence of crew coordination definitely influenced the flight.
First Officer de Fraia: This doesn't make sense to me.
Narrator: It seems that when the critical moment came and the captain had only a split-second to decide First Officer de Fraia: Go around! Captain Liberti: No, no, no, no.
Hold the glide.
Narrator: his opinion of the younger pilot may have coloured his decision.
Robert Benzon: When the first officer attempted the go around, the captain at that instant didn't trust him to make a good decision.
Hans-Peter Graf: If there had been a bit more trust between them, who knows? Investigators now understand the human factors that were at play.
But the technical failure at the heart of the accident needs further examination.
Other planes could be at risk.
Narrator: Investigators need to learn more about the DC-9's design.
Hans-Peter Graf: Thanks for coming right away.
Narrator: They want to know why the Alitalia crew were not warned when one of their Nav radios failed.
Hans-Peter Graf: We needed to work together with the manufacturer of the airplane, McDonnell Douglas.
Hans-Peter Graf: So this is the system they used for Nav 1.
McDonnell Douglas Rep: It's an older model, what's known as an unmonitored receiver.
Investigators learn that the receiver in question is a King KNR 60-30.
Unlike newer models, the King receiver doesn't monitor the signal it sends to the HSI.
This means it can't warn pilots if the signal becomes interrupted.
What's more, in the event of a short-circuit the glide slope indicator will display a centered or on glide position.
Hans-Peter Graf: This receiver should have been banned from any airplanes.
It should never have been possible to install them.
That is my opinion.
Hans-Peter Graf: So the pilots had no way to know that it had malfunctioned? McDonnell Douglas Rep: Well, there would be other clues in the cockpit.
Robert Benzon: Unfortunately there are devices within the cockpit that could have given them an indication of something going wrong.
They had a standby altimeter that wasn't affected by this navigation problem at all.
Hans-Peter Graf: Why didn't you warn the airlines? McDonnell Douglas Rep: We did.
We even had a seminar to inform pilots.
There were at least a couple of the Alitalia guys there.
Investigators are surprised to learn that six years earlier McDonnell Douglas sent a letter describing the problem to all DC-9 operators.
Russell Lawton: Whenever you possibly can you remove the hazard.
That's the first rule.
If you can't do that, the second rule is you warn the person about the hazard.
That's what they did in this case.
Hans-Peter Graf: So it looks like the airline really dropped the ball.
Todd Curtis: One can't rely on pilots overhearing something in a conference, then overhearing it at the break room and they implement changes.
That's not how it's done.
This is a very organized, very procedures-based world where learning has to go through a process.
Robert Benzon: For some reason, that information never drifted down to the line crew member level.
We were pretty convinced that the accident crew members had no idea this false reading could exist.
Narrator: Investigators now understand the sequence of events that doomed Alitalia 404.
It starts with an aging DC-9 carrying forty passengers, four flight attendants, two pilots and a hidden danger Captain Liberti: Do you have the glide slope? Narrator: A flaw in the navigation system.
First Officer de Fraia: On one.
Captain Liberti: Let's do it on one.
First Officer de Fraia: Radio one, confirmed.
Hans-Peter Graf: With this receiver, the best pilot in the world would be at risk.
Robert Benzon: It would fool anybody.
Narrator: On approach to Zurich, flight 404 descends below its intended glide path.
Air Traffic Controller: Alitalia 404, descend to 4000, turn right, heading one-one-zero.
The busy air traffic controller fails to notice.
The pilots also don't notice, perhaps because of a notoriously confusing altimeter.
Captain Liberti: Captured glide path so we're on the beam.
But certainly due to a false glide slope indication.
Hans-Peter Graf: Radio one had a on-glide slope indication telling him okay, we are fine.
We are on the correct flight path to the runway.
A disabled GPWS keeps them unaware of the danger until First Officer de Fraia: Go around! Captain Liberti: No, no, no, no.
Hold the glide.
The captain's lack of trust in his young First Officer seals their fate.
Todd Curtis: To pin the blame on any one of them, the pilots' role, the air traffic controller's role, the manufacturer of the technology, their role, is unfair.
This was a multiple input event.
Narrator: In its final report, the Swiss Air Accident Investigation Board calls for the prompt removal from service of all unmonitored radio receivers.
Hans-Peter Graf: If there is any doubt about the functioning of a, a piece of equipment that has to ensure the safe landing of an airplane, it has no place in the airplane any longer.
Narrator: They also recommend that airlines give first officers more authority in critical flight situations.
Franco Bergante: After the accident, the procedure was changed so that if the co-pilot sees something wrong and calls for a go around, and the captain doesn't execute it, he's authorized to do it by himself.
The accident brought important improvements to Zurich Airport as well.
Russell Lawton: It was after that that Zurich installed the minimum safe altitude warning system in its ATC facility.
And so unfortunately it took that tragedy to happen but, you know, at least some positive things resulted from it.
Robert Benzon: We learn from every accident.
Even though they're tragic events, frankly some good comes out of every single one of them.
And the recommendations that came out of this accident have led to an aviation system today that is very, very safe.
Captain Liberti: Hold the glide.
Narrator: Near Zurich Airport, a DC-9 plows into the ground six miles short of the runway.
Russell Lawton: It was a fatal loss of life.
It was a tragedy.
Ulrich Braun: You have impressions and smells that you never forget.
It changes you.
Hans-Peter Graf: Pitch and roll, fine.
Flaps, good.
No stabilization problems.
Narrator: Close analysis of the evidence only deepens the mystery.
Hans-Peter Graf: It was definitely flying too low but why, we didn't know.
Robert Benzon: Maybe it was something we can't see.
Narrator: Could a hidden fault deep inside the airplane have led the two pilots down a deadly path? Robert Benzon: That put all the other aircraft in the sky in danger.
Captain Liberti: Zurich, good evening.
Alitalia 4-0-4, descending one-zero-zero.
Echo received.
Air Traffic Controller: Alitalia 4-0-4, Zurich arrival.
Good evening.
Narrator: The crew of Alitalia flight 404 is nearing the end of an evening flight to Zurich, Switzerland.
Air Traffic Controller: Alitalia 4-0-4, fly heading three-two-five radar vectors to ILS fourteen.
Captain Liberti: Radar vectors to runway one-four on heading three-two-five.
Captain Raffaele Liberti is a senior Alitalia pilot with more than twenty years' experience.
First Officer de Fraia: How much is the visibility? Captain Liberti: Visibility is nine kilometers.
Narrator: First Officer Massimo de Fraia is the pilot flying the plane tonight.
He's new to the airline, having joined just last year.
Franco Bergante also flew for Alitalia in the 1990s.
Franco Bergante: At the time, it was one of the safest companies and best trained in the world.
I knew the captain very well, the co-pilot a little less.
Narrator: There are four flight attendants and forty passengers in the cabin.
Passenger: Thank you.
Narrator: Several of the passengers are Swiss industrial workers heading home after a lengthy stretch of work.
Passenger: Oh it'll be nice to get back, huh, after all this time away? Let's hope they recognize us.
Hans-Peter Graf: Typically the passengers were employees going back and forth, uh, from Switzerland to Italy, especially to Milan.
Narrator: The plane is a McDonnell Douglas DC-9 that's been flying since 1974.
Todd Curtis: The DC-9 was one of the mainstays of the industry from the 1960s through the 2000s.
It was very, very popular in the U.
S, Western Europe and around the world, primarily for shorter regional trips.
Franco Bergante: Even if it wasn't among the more modern planes, it was a good airplane.
Narrator: Flight 404 left Milan's Linate Airport twenty-five minutes ago.
The flight path takes it almost directly north over the Alps to Zurich's Kloten Airport.
Air Traffic Controller: Lufthansa 1-8-7-3, maintain two-four-zero.
Narrator: At Zurich air traffic control, it's a busy evening.
Air Traffic Controller: Swiss 3-6-1-1, maintain two-three-zero.
Narrator: The airport is one of Europe's main hubs, serving 12 million passengers a year.
Air Traffic Controller: Alitalia 4-0-4, turn right heading three-four-zero.
Captain Liberti: Right three-four-zero, Alitalia 4-0-4.
Narrator: Alitalia 404 is lining up for its approach to the airport.
Captain Liberti: You should slow down a bit.
The faster you go, the less time you have for landing.
Air Traffic Controller: Alitalia 4-0-4, reduce to two-one-zero knots.
Captain Liberti: Two-one-zero knots reducing, 4-0-4.
You see? Narrator: The pilots are preparing for what's called an ILS or instrument landing system approach.
Todd Curtis: An instrument landing system is a series of technologies, primarily radio transmitters on the ground, that allows an aircraft to align itself both vertically and horizontally with the runway.
Air Traffic Controller: Alitalia 4-0-4, reduce to one-eight-zero knots.
Captain Liberti: Reducing one-eight-zero, 4-0-4.
Do you have the glide slope? First Officer de Fraia: Uh, it's on one Captain Liberti: Let's do it on one.
Narrator: The crew sets the navigation instruments to pick up the ILS signal from the runway.
First Officer de Fraia: Radio one confirmed.
Todd Curtis: There is a set of signals, which goes out at an angle from the ground that gives them an idea of the glide slope, which is typically around a three degree slope.
Robert Benzon: It gives you one tiny pencil thin beam that you can fly down that ensures that you're going to stay above the trees and not hit anything below there and it'll, it'll lead you right to the end of the runway.
Air Traffic Controller: Alitalia 4-0-4, reduce to one-six-zero knots.
Captain Liberti: Reducing one-six-zero.
Captured LOC.
Captured glide path so we're on the beam.
Narrator: Flight 404 is third in line on approach, the runway 12 miles straight ahead.
The pilots can't see it yet, but their navigation instruments show they are locked on to the proper signals.
All they need to do now to finalize the approach is intercept a radio beacon known as the outer marker.
Hans-Peter Graf: The outer marker is something like the last occasion to check whether the ILS is correct.
Todd Curtis: That tells them as they get closer that they're still right on the money.
First Officer de Fraia: Flaps 25.
Captain Liberti: Flaps 25.
The outer marker check is at 1,250 feet, almost four miles.
First Officer de Fraia: Didn't we pass it? Didn't we pass the outer marker? Captain Liberti: No.
No, it hasn't changed yet.
Air Traffic Controller: Alitalia 4-0-4, speed as convenient.
Contact tower one-one-eight-point-one.
Captain Liberti: One-one-eight-point-one, good-bye.
First Officer de Fraia: That doesn't make sense to me.
Narrator: The runway should be just ahead.
But the first officer still can't see it.
Something's not right.
First Officer de Fraia: Go around.
Captain Liberti: No, no, no, no.
Hold the glide.
Can you hold it? First Officer de Fraia: Yes, sir.
Captain Liberti: Ah! Air Traffic Controller: Lufthansa 1-0-3-4, reduce to one-six-zero knots.
Alitalia 4-0-4.
Narrator: The controller has no idea why Alitalia 404 has suddenly disappeared from radar.
Rabbit 932 Pilot: Rabbit 9-3-2, established ILS 14.
Air Traffic Controller: Rabbit 9-3-2, do you see an aircraft ahead of you? Rabbit 932 Pilot: Standby.
No traffic in sight but there's fire on the ground.
Air Traffic Controller: Roger.
Narrator: It can only mean one thing.
Air Traffic Controller: This is air traffic control.
We have an emergency.
Narrator: Swiss and German firefighters rush to the site of the crash of Alitalia flight 404, a forested hillside six miles from Zurich's Kloten Airport.
Ulrich Braun: At first, you could see a glow in the woods and there was a taste of burning rubber and when we could finally see the actual crash site it was horrific.
(SPEAKING FOREIGN LANGUAGE) Narrator: The plane has cut a swathe through the trees, scorching the surrounding area.
The scale of the destruction is staggering.
Ulrich Braun: The airplane was completely destroyed.
The main goal was to save people.
Narrator: But as fire crews suppress the flames and comb through charred debris, they can find no one to save.
All forty-six people aboard the flight are dead.
Franco Bergante: I was very upset because it was a loss of someone close.
Ulrich Braun: You have images that you have to deal with.
You have impressions and smells that you never forget.
It changes you.
Narrator: With the wreckage still smoldering, an investigation into what happened is already underway.
Hans-Peter Graf is with Switzerland's Air Accident Investigation Bureau, or AAIB.
Hans-Peter Graf: The first thought is: Well, bad news.
It's gonna be a big and long investigation.
I had to get a first impression of what had actually happened that night.
So I went straight to air traffic control center in Zurich.
Hans-Peter Graf: Hello.
Good evening.
Air Traffic Controller: Good evening.
Narrator: Graf meets with the last person to speak to the Alitalia crew.
Hans-Peter Graf: What can you tell me about flight 404? Hans-Peter Graf: I hoped to learn if the crew had issued an emergency beforehand, if there was anything unusual about the airplane.
Air Traffic Controller: It was routine.
Uh they were making an ILS approach, as usual.
They never reported any problems.
Hans-Peter Graf: Can you replay the radar track? Air Traffic Controller: Yes, of course.
Narrator: Graf knows that most control centers keep recordings of all recent radar tracks.
Hans-Peter Graf: I had a closer look at the radar screen itself.
I saw the airplane symbol AZ 404 together with the altitude reading on the screen.
Hans-Peter Graf: Well, they may not have reported a problem, but they sure had one.
Look at that glide slope.
Graf discovers that more than five minutes before the crash, flight 404 was already too low and descending lower.
Hans-Peter Graf: I noticed that the airplane was flying 1,200 feet below the actual flight path.
Narrator: The proper glide slope would have taken the DC-9 on a gradual descent right to the foot of the runway.
Instead, the plane flew an almost parallel path more than a thousand feet lower right into the side of a small mountain.
Hans-Peter Graf: You didn't notice their altitude? Air Traffic Controller: Well, I was juggling six flights.
All the 404 calls were normal.
They said they were on glide.
Todd Curtis: That particular controller would assume if they were reporting they were lined up with the runway and that they were on the glide path that they were safely above any terrain.
Hans-Peter Graf: And your minimum safe altitude warning system didn't sound? Air Traffic Controller: We don't have one installed as of yet.
Russell Lawton: Unfortunately at the time, you know, they didn't have the minimum safe altitude warning system in place in Zurich.
In the U.
S, it had already been in place for ten years.
Hans-Peter Graf: You said they were doing an ILS approach.
Air Traffic Controller: Mm hmm.
Hans-Peter Graf: Then we don't have a choice.
Shut the system down immediately.
We can't risk another flight.
Narrator: Graf worries the runway guidance system may be malfunctioning.
A full test of the system will cause major disruptions for Zurich Airport, but it has to be done.
Robert Benzon: If the ground transmitter was malfunctioning, that put all the other aircraft in the sky in danger.
So they have to shut it down until they, they have it checked out by electronic technicians.
Narrator: It could take a day or more to get results, but if the testing reveals a fault with the ILS it could explain why Alitalia flight 404 ended in tragedy.
Daylight reveals a 300-meter long scar through a hillside forest northwest of Zurich where Alitalia 404 crashed hours earlier.
Joining the investigation is Bob Benzon of the US National Transportation Safety Board.
Robert Benzon: Because the aircraft was manufactured in the United States, our role was really to assist the Swiss government in determining what happened.
Robert Benzon: That's a lot of fire damage.
It's gonna make ID'ing parts a real chore.
Robert Benzon: The thing that stuck out was the amount of destruction.
The only truly recognizable things were the engines and the landing gear.
But the rest of it was pretty well burnt up.
Robert Benzon: Let's see that map again.
Narrator: Investigators wonder what the mangled terrain can tell them about the plane's last moments.
Robert Benzon: It looked to us like the aircraft had, had struck the trees in a bit of a level attitude, although parts of the right wing had, had been sheared off by the trees and that caused a more lift to occur on the left side of the aircraft, causing the aircraft to roll.
So the eventual impact was nearly inverted.
(PHONE RINGING) Robert Benzon: Hello.
Benzon.
Benzon gets word on Zurich Airport's instrument landing system.
Robert Benzon: That's for certain? Okay.
Narrator: Overnight testing has revealed that the guidance technology is in perfect working order.
Captain Liberti: Captured LOC.
Captured glide path, so we're on the beam.
Narrator: It means the ILS was sending the proper signal throughout flight 404's descent to the airport.
Robert Benzon: The ILS is fine.
So whatever brought that plane down, the evidence has gotta be here somewhere.
Robert Benzon: That led us to believe that perhaps there was a problem onboard the aircraft rather than on the ground.
Narrator: More answers about the mysterious crash may be close at hand.
The team has recovered both of the plane's black boxes.
But they won't know if the data they need has survived the crash until they get the recorders to a lab for analysis.
Hans-Peter Graf: So they were cleared for runway 14.
It looks like they're on the right heading.
They're way too low.
It's like they don't even know the hill's there.
I wonder how well the pilots knew the route.
Narrator: Searching for answers, investigators look into the pilots' work records.
They discover that besides being a senior Alitalia pilot, the captain was also a former military airman.
Robert Benzon: We learned that the captain had over 10,000 flying hours.
Captain Liberti: Zurich, good evening.
Alitalia 404, descending one-zero-zero, echo received.
What's more, the Milan to Zurich route was nothing new to him.
Hans-Peter Graf: The captain, who was flying this route many times in his career, was very familiar with it.
Narrator: They learn that the 28-year-old first officer was far less experienced.
But his record is spotless, and he'd also landed at Zurich before.
Robert Benzon: Both pilots had flown this route many times before in the same cockpit sometimes.
So they were familiar with what the approach should look like.
Narrator: Across Zurich and throughout Europe, news of the crash has left people rattled.
The quiet city, best known for its banking sector, hasn't seen a major air disaster in almost 20 years.
Russell Lawton: It was such a tragedy.
It was an all-fatal loss of life and so it was reported in the media extensively.
Narrator: The media attention puts mounting pressure on investigators.
Hans-Peter Graf: Is this the flight data? Narrator: Finally, they have some good news.
Information from both the flight data recorder and the cockpit voice recorder has survived.
Hans-Peter Graf: We should get this up on the projector.
Narrator: But will it provide the answers investigators need? Russell Lawton: Was there an aircraft malfunction of some sort? An instrument failure? A flight crew problem? Those are the immediate things that you zero in on.
Robert Benzon: Well, there's not a lot of parameters but it should tell us something.
Narrator: Investigators begin with the flight data, looking for any sign of a mechanical problem onboard.
Hans-Peter Graf: Thrust is good.
Robert Benzon: Although the thing was reasonably ancient compared to the modern ones, it only had 10 parameters, two of those parameters were engine pressure ratio, which means how much thrust the engines were putting out.
And they showed us that the engines were operating normally up until the time of impact.
Hans-Peter Graf: Pitch and roll, fine.
Flaps, good.
Robert Benzon: Yup.
Hans-Peter Graf: No stabilization problems.
Everything seems normal from a mechanical standpoint.
Robert Benzon: Even the glide is smooth and straight.
It's just all over a thousand feet too low.
I don't get it.
Narrator: The data doesn't reveal any mechanical failure that can explain the crash.
It only confirms the mysterious glide path recorded by air traffic control radar.
Hans-Peter Graf: On the FDR data, we could not find any technical issues at all.
The airplane performed as per design.
It was definitely flying too low, but why, we didn't know.
Hans-Peter Graf: Please set up the playback machine.
We need to hear what was going on in that cockpit.
Trying to understand why a well-trained Alitalia crew flew their DC-9 into the ground miles short of the runway, investigators now turn to the cockpit recording.
Robert Benzon: Something was going wrong with the perceptions of the crew, perhaps the aircraft itself, to cause it to be almost a thousand feet, maybe a little bit more, below where it should have been on the approach.
So that became a focus.
Captain Liberti: (Static) But as soon as they start listening to the recording, they know they have a problem.
Hans-Peter Graf: There was a lot of, of noise and, uh, it was first of all difficult to understand.
Hans-Peter Graf: It sounds like they weren't using their headsets for some reason.
Captain Liberti: You should slow down a bit.
Robert Benzon: The flight crew weren't using boom microphones.
They were just talking into one single microphone located in the middle of the instrument panel.
Captain Liberti: The faster you go, the less time you have for landing.
Todd Curtis: So this led to some of the words not being understood by the accident investigators.
Hans-Peter Graf: Send it back to the lab.
We won't be able to get anything off this.
Narrator: It's a disappointing setback.
Investigators can only hope lab technicians can find a way to filter out the noise and produce an audible recording.
Robert Benzon: So it was very difficult for the investigators to create a true transcript.
Narrator: In a facility at Zurich airport, investigators survey wreckage recovered from Alitalia flight 404.
They're looking for any clue that might help explain why the DC-9 flew for more than five minutes on a fatally low glide path before plowing into a hillside.
Robert Benzon: I'm surprised there are planes that still have this altimeter.
They're ancient.
What if they misread their altitude? Narrator: The DC-9's cockpit was equipped with what's known as a drum pointer altimeter.
Hans-Peter Graf: The drum pointer altimeter is known to be prone to be misread.
Robert Benzon: You have to look at the drum, and then you have to look at the needle.
And it's almost like an analogue watch versus a digital watch.
Narrator: Unlike a modern digital altimeter, the drum pointer design can only be read in two steps.
Feet in thousands is indicated on a drum like an odometer in a car.
Feet in hundreds is indicated by a pointer that moves around a scale like a clock face.
The problem with the design is as it moves the pointer can sometimes obstruct the pilots' view of the numbers on the drum.
Todd Curtis: If that needle happened to be obscuring part of the odometer that showed the thousands of feet, there could be some confusion as to whether it was one particular altitude or maybe a thousand feet away from that, so the potential for confusion existed.
Narrator: The industry has been phasing out the notoriously confusing instrument for years, but it's still found on older planes like DC-9s from the mid-70s.
At this stage in the investigation, the team has no way of knowing if the pilots misread the instrument.
Robert Benzon: If they did misread it, that could explain why they were so low on approach.
But the GPWS would have warned them.
The ground proximity warning system, or GPWS, is an onboard technology designed to help pilots avoid terrain.
The system bounces radio waves off the ground below to measure altitude and sounds a cockpit warning if the plane gets too low.
Robert Benzon: And there's no mistaking that alarm.
Narrator: Investigators know the Alitalia DC-9 was equipped with a GPWS, but did the pilots get a warning before the fatal impact? Robert Benzon: We really need that CVR.
Robert Benzon: Hey.
Hans-Peter Graf: Hey.
Robert Benzon: All right.
This is the proper glide slope for runway 14.
Hans-Peter Graf: Right.
I've got the transcript for the enhanced recording.
Narrator: They hope to finally get some answers from the cockpit recording, now cleaned up by audio technicians and ready for playback.
Todd Curtis: The picture that was given by the full transcript is more than enough to get a very good idea of what the sequence of events was in the cockpit.
Hans-Peter Graf: Okay.
First Officer de Fraia: Then we do a radio approach? Captain Liberti: Yes.
Hans-Peter Graf: They're at just over 4,000 feet here, which is well below the glide slope.
Robert Benzon: Okay, so but they need to level off to capture the glide but they kept descending.
First Officer de Fraia: On one Captain Liberti: Let's do it on one.
First Officer de Fraia: Radio one confirmed.
Hans-Peter Graf: It sounds like they're just on radio one.
Narrator: ILS transmitters send radio signals to two navigational receivers in the cockpit, Nav Radio 1 and Nav Radio 2.
The pilots can use either one to guide the plane.
Investigators now know the crew selected Nav Radio 1.
But they're still hoping to discover something about the unusual low glide slope and about the GPWS.
Air Traffic Controller: Alitalia 404, reduce to one-six-zero knots.
Captain Liberti: Reducing one-six-zero.
Captured glide path so we're on the beam.
Robert Benzon: Stop it there.
On the beam? They're well below the glide slope there.
Hans-Peter Graf: They are more than 1000 feet below it.
Robert Benzon: So why is the captain saying then that he captured it? What they're hearing from the cockpit only deepens the mystery.
Investigators know that right in front of both pilots is an instrument that should be showing their exact glide slope position.
It's called a glide slope indicator.
Todd Curtis: There are visual cues, specific systems that are in place that give a pilot an idea of whether or not they're too high or too low on the glide slope.
Robert Benzon: Did they misread the altimeter and the glide slope? I mean that doesn't seem possible.
Hans-Peter Graf: Let's keep listening for the GPWS.
Robert Benzon: Okay.
First Officer de Fraia: Flaps 25.
Captain Liberti: Flaps 25.
The outer marker check is at 1,250 feet, almost four miles.
First Officer de Fraia: Didn't we pass it? Didn't we pass the outer marker? Captain Liberti: No.
No, it hasn't changed yet.
Hans-Peter Graf: Something in that cockpit is confusing these pilots.
Air Traffic Controller: Alitalia 404, speed as convenient, contact tower one-one-eight-point-one.
Captain Liberti: One-one-eight-point-one, goodbye.
First Officer de Fraia: That doesn't make sense to me.
Go around.
Captain Liberti: No, no, no.
Hold the glide.
Robert Benzon: The CVR had the first officer attempting to go around and then being countermanded by the captain.
There was a lot of confusion there.
- Captain Liberti: Can you hold it? - First Officer de Fraia: Yes, sir.
Captain Liberti: Ah! Narrator: Investigators are stunned both by what they've heard and by what they haven't heard.
Hans-Peter Graf: No ground proximity warnings at all.
Robert Benzon: The fact that the aircrew didn't get a warning from the ground proximity warning system, uh, was a surprise to us.
Robert Benzon: And the captain called off a go around.
They now face more questions than ever.
How could two professional pilots both misread their glide slope indicators? Why did the plane's ground proximity warning not sound? First Officer de Fraia: Go around.
Captain Liberti: No, no, no, no.
And why did the captain call off the one maneuver that might have saved his plane and his passengers? Robert Benzon: This one looks pretty beat up too.
Investigators examine a pair of flight instruments recovered from the cockpit of Alitalia 404 - the heading indicators, known as HSIs.
They hope the damaged instruments can confirm whether or not the pilots misread their glide slope on approach to Zurich.
Hans-Peter Graf: They recovered the HSI from the wreckage, and we wanted to know what was the indication of the glide slope.
Robert Benzon: Okay, so that mark there, is that the same as on the first one? Narrator: They closely examine a small arrow on the glide slope indicator situated on the right side of each HSI.
It's the instrument that tells the pilots if they're flying too high or too low.
Robert Benzon: We found what we call slap marks, which means the indicator as it was being destroyed, uh, the needles on the indicator slapped against the background.
So at the time of impact you could determine what that instrument was showing you.
Todd Curtis: It did have markings on it showing that they were on glide slope.
Robert Benzon: So they were both indicating on glide.
Narrator: It's a major discovery.
It means that both indicators were on the glide slope and the pilots didn't misread them.
Captain Liberti: Captured LOC.
Captured glide path so we're on the beam.
Narrator: The captain announced capture because his instrument was showing him he was on the proper descent path even though he was actually more than a thousand feet below it.
Franco Bergante: They got what's called a false glide slope.
Robert Benzon: And that kind of led us to wonder how that could occur.
The team now needs to understand why critical cockpit instruments were displaying the wrong glide slope.
With help from Alitalia, they begin examining the onboard source of that information, the number one navigation receiver.
Did the unit have some kind of defect that caused it to send a faulty signal? Hans-Peter Graf: I couldn't understand why can the autopilot fly a faulty glide path, why the pilots don't get warned about that.
There must be something totally wrong with this receiver.
Robert Benzon: I don't see any corrosion.
All the internal components seem to be in the right place.
No obvious defects.
Maybe it's something that we can't see like a short-circuit.
Robert Benzon: Well, we had a very good idea that the Nav 1 receiver was, was putting out false information.
But we couldn't directly test it because of damage to the device during the accident sequence.
So the Swiss investigators decided to do some testing.
Narrator: Investigators start by deliberately shorting-out a Nav 1 receiver and then testing it in a flight simulator to see what happens.
Hans-Peter Graf: Okay.
It should be in the menu.
I pre-programmed the route as 404 approach.
Russell Lawton: Simulation tests are important during an accident investigation because what you're trying to do is recreate the scenario and circumstances that led up to the accident.
Then they simulate the flight path of Alitalia 404.
Hans-Peter Graf: We're 15 miles out, 1200 feet below glide.
Stand by.
Narrator: Graf wants to see if he can reproduce the same false glide path that deceived the Alitalia crew.
Hans-Peter Graf: Switch to Radio 1.
There it is! Narrator: A false glide indication on the display.
Hans-Peter Graf: And no warning flags.
Narrator: Graf is stunned to see that the short-circuited receiver defaults to the on-glide position and that there's no warning about the malfunction.
Todd Curtis: Typically if the signals are not correct there's some sort of warning given in the instrument itself.
There was no warning.
Hans-Peter Graf: I was really surprised that somebody could design a piece of equipment without warning the pilots if there is something wrong with it.
Robert Benzon: It was a, uh, kind of an aha moment.
Captain Liberti: Captured LOC.
Captured glide path so we're on the beam.
Narrator: There was now no doubt that a short-circuit in the Nav 1 receiver caused the deadly glide slope display malfunction.
Did it also somehow disable the potentially lifesaving ground proximity warning? Hans-Peter Graf: Keep going.
Narrator: That's what Graf wants to know next.
Hans-Peter Graf: Thirty seconds from impact.
The simulation soon gives him an answer.
Hans-Peter Graf: Nothing.
It should have sounded by now.
The plane's GPWS never sounds a warning.
Robert Benzon: And it turns out that if the navigation radios aren't putting out a good signal to the rest of the aircraft, the GPWS it just doesn't work.
Narrator: The GPWS finding leads to another disturbing question.
First Officer de Fraia: That doesn't make sense to me.
Narrator: Would the crew have been able to save their plane and 40 passengers First Officer de Fraia: Go around! Captain Liberti: No, no, no, no.
Hold the glide.
Narrator: if the captain had initiated a go around when his first officer called for it? Hans-Peter Graf: Okay, so no hesitation when I give the order, okay? We're almost there.
Five, four, three, two, one.
Go around.
Climbing safely.
Those poor bastards.
Hans-Peter Graf: Had the captain not intervened they would have made it.
Robert Benzon: The aircraft would have passed over the top of the mountain without striking it.
Not, not by much, you know, a couple hundred feet perhaps.
Narrator: It's a heartbreaking discovery, one that motivates investigators to try to understand why the fatal decision was made.
Why did a seasoned pilot overrule his first officer and miss his last chance to avoid disaster? Hans-Peter Graf: Let's take it from earlier in the flight.
Narrator: For more insight into what the captain may have been thinking, they return to the cockpit voice recording.
First Officer de Fraia: How is it approaching? Captain Liberti: Approaching, turning left to Schaffhausen.
Narrator: They listen from earlier in the approach to try to get a sense of how well the pilots were working together.
Captain Liberti: I told you not to go on that beacon.
Robert Benzon: Well, it was a crew that had a very experienced fellow in the left seat and a very inexperienced fellow in the right seat, and that always causes a bit, a bit of consternation at times during a flight.
Captain Liberti: Go to the left.
You see? You'd moved.
What emerges is troubling.
The captain seems constantly dissatisfied with his first officer.
Captain Liberti: It's compulsory to go there.
Todd Curtis: There seemed to be some sort of a mentor/student relationship, the first officer being admonished at some points by the captain.
Captain Liberti: You should slow down a bit.
The faster you go the less time you have for landing.
Air Traffic Controller: Alitalia 404, reduce to two-one-zero knots.
Captain Liberti: Two-one-zero knots reducing, 404.
You see? Hans-Peter Graf: My impression is that the captain didn't trust the co-pilot's abilities because he, he already showed that he wasn't very sure what he was doing.
Robert Benzon: Not exactly an ideal working relationship.
Franco Bergante: The captain was a bit tough.
And the co-pilot was a bit weak.
So let's say that the absence of crew coordination definitely influenced the flight.
First Officer de Fraia: This doesn't make sense to me.
Narrator: It seems that when the critical moment came and the captain had only a split-second to decide First Officer de Fraia: Go around! Captain Liberti: No, no, no, no.
Hold the glide.
Narrator: his opinion of the younger pilot may have coloured his decision.
Robert Benzon: When the first officer attempted the go around, the captain at that instant didn't trust him to make a good decision.
Hans-Peter Graf: If there had been a bit more trust between them, who knows? Investigators now understand the human factors that were at play.
But the technical failure at the heart of the accident needs further examination.
Other planes could be at risk.
Narrator: Investigators need to learn more about the DC-9's design.
Hans-Peter Graf: Thanks for coming right away.
Narrator: They want to know why the Alitalia crew were not warned when one of their Nav radios failed.
Hans-Peter Graf: We needed to work together with the manufacturer of the airplane, McDonnell Douglas.
Hans-Peter Graf: So this is the system they used for Nav 1.
McDonnell Douglas Rep: It's an older model, what's known as an unmonitored receiver.
Investigators learn that the receiver in question is a King KNR 60-30.
Unlike newer models, the King receiver doesn't monitor the signal it sends to the HSI.
This means it can't warn pilots if the signal becomes interrupted.
What's more, in the event of a short-circuit the glide slope indicator will display a centered or on glide position.
Hans-Peter Graf: This receiver should have been banned from any airplanes.
It should never have been possible to install them.
That is my opinion.
Hans-Peter Graf: So the pilots had no way to know that it had malfunctioned? McDonnell Douglas Rep: Well, there would be other clues in the cockpit.
Robert Benzon: Unfortunately there are devices within the cockpit that could have given them an indication of something going wrong.
They had a standby altimeter that wasn't affected by this navigation problem at all.
Hans-Peter Graf: Why didn't you warn the airlines? McDonnell Douglas Rep: We did.
We even had a seminar to inform pilots.
There were at least a couple of the Alitalia guys there.
Investigators are surprised to learn that six years earlier McDonnell Douglas sent a letter describing the problem to all DC-9 operators.
Russell Lawton: Whenever you possibly can you remove the hazard.
That's the first rule.
If you can't do that, the second rule is you warn the person about the hazard.
That's what they did in this case.
Hans-Peter Graf: So it looks like the airline really dropped the ball.
Todd Curtis: One can't rely on pilots overhearing something in a conference, then overhearing it at the break room and they implement changes.
That's not how it's done.
This is a very organized, very procedures-based world where learning has to go through a process.
Robert Benzon: For some reason, that information never drifted down to the line crew member level.
We were pretty convinced that the accident crew members had no idea this false reading could exist.
Narrator: Investigators now understand the sequence of events that doomed Alitalia 404.
It starts with an aging DC-9 carrying forty passengers, four flight attendants, two pilots and a hidden danger Captain Liberti: Do you have the glide slope? Narrator: A flaw in the navigation system.
First Officer de Fraia: On one.
Captain Liberti: Let's do it on one.
First Officer de Fraia: Radio one, confirmed.
Hans-Peter Graf: With this receiver, the best pilot in the world would be at risk.
Robert Benzon: It would fool anybody.
Narrator: On approach to Zurich, flight 404 descends below its intended glide path.
Air Traffic Controller: Alitalia 404, descend to 4000, turn right, heading one-one-zero.
The busy air traffic controller fails to notice.
The pilots also don't notice, perhaps because of a notoriously confusing altimeter.
Captain Liberti: Captured glide path so we're on the beam.
But certainly due to a false glide slope indication.
Hans-Peter Graf: Radio one had a on-glide slope indication telling him okay, we are fine.
We are on the correct flight path to the runway.
A disabled GPWS keeps them unaware of the danger until First Officer de Fraia: Go around! Captain Liberti: No, no, no, no.
Hold the glide.
The captain's lack of trust in his young First Officer seals their fate.
Todd Curtis: To pin the blame on any one of them, the pilots' role, the air traffic controller's role, the manufacturer of the technology, their role, is unfair.
This was a multiple input event.
Narrator: In its final report, the Swiss Air Accident Investigation Board calls for the prompt removal from service of all unmonitored radio receivers.
Hans-Peter Graf: If there is any doubt about the functioning of a, a piece of equipment that has to ensure the safe landing of an airplane, it has no place in the airplane any longer.
Narrator: They also recommend that airlines give first officers more authority in critical flight situations.
Franco Bergante: After the accident, the procedure was changed so that if the co-pilot sees something wrong and calls for a go around, and the captain doesn't execute it, he's authorized to do it by himself.
The accident brought important improvements to Zurich Airport as well.
Russell Lawton: It was after that that Zurich installed the minimum safe altitude warning system in its ATC facility.
And so unfortunately it took that tragedy to happen but, you know, at least some positive things resulted from it.
Robert Benzon: We learn from every accident.
Even though they're tragic events, frankly some good comes out of every single one of them.
And the recommendations that came out of this accident have led to an aviation system today that is very, very safe.