What Really Happened Aboard Air France 447

[N Harmon]

http://www.popularmechanics.com/technology/aviation/crashes/what-really-happened-aboard-air-france-447-6611877

Bonin's behavior is difficult for professional aviators to understand. "If he's going straight and level and he's got no airspeed, I don't know why he'd pull back," says Chris Nutter, an airline pilot and flight instructor. "The logical thing to do would be to cross-check"—that is, compare the pilot's airspeed indicator with the co-pilot's and with other instrument readings, such as groundspeed, altitude, engine settings, and rate of climb. In such a situation, "we go through an iterative assessment and evaluation process," Nutter explains, before engaging in any manipulation of the controls. "Apparently that didn't happen."

[...]

The Airbus's stall alarm is designed to be impossible to ignore. Yet for the duration of the flight, none of the pilots will mention it, or acknowledge the possibility that the plane has indeed stalled—even though the word "Stall!" will blare through the cockpit 75 times. Throughout, Bonin will keep pulling back on the stick, the exact opposite of what he must do to recover from the stall.

[...]

Still, the pilots continue to ignore it, and the reason may be that they believe it is impossible for them to stall the airplane. It's not an entirely unreasonable idea: The Airbus is a fly-by-wire plane; the control inputs are not fed directly to the control surfaces, but to a computer, which then in turn commands actuators that move the ailerons, rudder, elevator, and flaps. The vast majority of the time, the computer operates within what's known as normal law, which means that the computer will not enact any control movements that would cause the plane to leave its flight envelope. "You can't stall the airplane in normal law," says Godfrey Camilleri, a flight instructor who teaches Airbus 330 systems to US Airways pilots.

But once the computer lost its airspeed data, it disconnected the autopilot and switched from normal law to "alternate law," a regime with far fewer restrictions on what a pilot can do. "Once you're in alternate law, you can stall the airplane," Camilleri says.

It's quite possible that Bonin had never flown an airplane in alternate law, or understood its lack of restrictions. According to Camilleri, not one of US Airway's 17 Airbus 330s has ever been in alternate law. Therefore, Bonin may have assumed that the stall warning was spurious because he didn't realize that the plane could remove its own restrictions against stalling and, indeed, had done so.

[...]

Unlike the control yokes of a Boeing jetliner, the side sticks on an Airbus are "asynchronous"—that is, they move independently. "If the person in the right seat is pulling back on the joystick, the person in the left seat doesn't feel it," says Dr. David Esser, a professor of aeronautical science at Embry-Riddle Aeronautical University. "Their stick doesn't move just because the other one does, unlike the old-fashioned mechanical systems like you find in small planes, where if you turn one, the [other] one turns the same way." Robert has no idea that, despite their conversation about descending, Bonin has continued to pull back on the side stick.

The men are utterly failing to engage in an important process known as crew resource management, or CRM. They are failing, essentially, to cooperate. It is not clear to either one of them who is responsible for what, and who is doing what. This is a natural result of having two co-pilots flying the plane. "When you have a captain and a first officer in the cockpit, it's clear who's in charge," Nutter explains. "The captain has command authority. He's legally responsible for the safety of the flight. When you put two first officers up front, it changes things. You don't have the sort of traditional discipline imposed on the flight deck when you have a captain."

[...]

As the stall warning continues to blare, the three pilots discuss the situation with no hint of understanding the nature of their problem. No one mentions the word "stall." As the plane is buffeted by turbulence, the captain urges Bonin to level the wings—advice that does nothing to address their main problem. The men briefly discuss, incredibly, whether they are in fact climbing or descending, before agreeing that they are indeed descending. As the plane approaches 10,000 feet, Robert tries to take back the controls, and pushes forward on the stick, but the plane is in "dual input" mode, and so the system averages his inputs with those of Bonin, who continues to pull back. The nose remains high.

02:13:40 (Robert) Remonte... remonte... remonte... remonte...
Climb... climb... climb... climb...

02:13:40 (Bonin) Mais je suis à fond à cabrer depuis tout à l'heure!
But I've had the stick back the whole time!

At last, Bonin tells the others the crucial fact whose import he has so grievously failed to understand himself.

02:13:42 (Captain) Non, non, non... Ne remonte pas... non, non.
No, no, no... Don't climb... no, no.

02:13:43 (Robert) Alors descends... Alors, donne-moi les commandes... À moi les commandes!
Descend, then... Give me the controls... Give me the controls!

Bonin yields the controls, and Robert finally puts the nose down. The plane begins to regain speed. But it is still descending at a precipitous angle. As they near 2000 feet, the aircraft's sensors detect the fast-approaching surface and trigger a new alarm. There is no time left to build up speed by pushing the plane's nose forward into a dive. At any rate, without warning his colleagues, Bonin once again takes back the controls and pulls his side stick all the way back.

02:14:23 (Robert) Putain, on va taper... C'est pas vrai!
[darn] it, we're going to crash... This can't be happening!

02:14:25 (Bonin) Mais qu'est-ce que se passe?
But what's happening?

02:14:27 (Captain) 10 degrès d'assiette...
Ten degrees of pitch...

Exactly 1.4 seconds later, the cockpit voice recorder stops.

[Spaceman3750]

I remember watching a special on flight 447. If I recall, they concluded that the primary cause of the accident was the icing of all pitot tubes and the pilot's subsequent failure to set correct pitch and power for continued safe airspeed (they said there's some magic numbers, something like 10 degrees pitch and 87% power or something like that). You can pick it up off of Netflix, it's pretty interesting.

[JeffDG]

While the pitot icing may have contributed, the cause of the crash as the pilots not flying the airplane.

This should be mandatory viewing for anyone flying a technically advanced aircraft, right from the G1000 on up to the A380
Untitled

[N Harmon]

I remember watching a special on flight 447. If I recall, they concluded that the primary cause of the accident was the icing of all pitot tubes and the pilot's subsequent failure to set correct pitch and power for continued safe airspeed (they said there's some magic numbers, something like 10 degrees pitch and 87% power or something like that). You can pick it up off of Netflix, it's pretty interesting.

That was the conclusion before the flight data recorder was recovered. Now it is clear the primary cause is human error

02:10:55 (Robert) Putain!
[darn] it!

Another of the pitot tubes begins to function once more. The cockpit's avionics are now all functioning normally. The flight crew has all the information that they need to fly safely, and all the systems are fully functional. The problems that occur from this point forward are entirely due to human error.

[sardak]

The pitot tubes iced over causing erroneous readings to the instruments but the #2 and #3 pilots (the captain was on his rest break) didn't respond properly to what they were seeing on the instruments. They put the aircraft in a nose up attitude, climbed from FL 350 to 380 and stalled the plane. The stall horn would sound intermittently, going silent when the flight computers received bad data.

By the time the captain got to the cockpit and figured out what was going on, it was too late to recover. The plane was intact when it hit the ocean, at a descent rate of -11,000 feet per minute, ground speed of 107 kts, pitch attitude 16 degrees nose up, wings almost level. The angle of attack during the 38,000 foot descent was always above 35 degrees.

Popular Mechanics must be looking to boost its circulation and/or promote the book by the French author. There's nothing new in the article. The flight recorders were found this past spring and the CVR transcript, sequenced to events on the FDR, was released in an interim report back in July. All of the information gathered to date is available on the BEA (Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile, similar to the NTSB) website. The combined CVR-FDR transcript starts on page 85 of the third interim report: http://www.bea.aero/docspa/2009/f-cp090601e3.en/pdf/f-cp090601e3.en.pdf

Links to all the reports, photos, data, etc. are on the homepage of the investigation: http://www.bea.aero/en/enquetes/flight.af.447/flight.af.447.php

Another source of good information is on the Professional Pilots Rumor Network forum, which has posts by some smart and knowledgeable people. The problem is that the thread is over 10,000 posts and is broken into seven sections (so far) more or less corresponding with the phases of the search and investigation. There are links to technical reports that aren't directly related to the accident, but on issues it raises such as fly-by-wire, flight controls, human factors, etc . http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a.html

Mike

[simon]

What happened was that a large part of the the aviation community finally became aware of what was known to a relatively small number of highly experienced pilots whose protests at the Airbus design approach fell on deaf ears - and that is that when it all hits the fan, high levels of automation can work against a pilot's instinct and certainly cannot make up for lack of training, especially in complex emergency situations.

A lot of Airbus pilots love the plane. Every Boeing pilot I have spoken to either dislikes or flat out hates it. There are about 5 or 10 things that they consider a fundamentally bad idea in an aircraft. The best thing that came out of this crash is pressure on Airbus to rethink their design and for Air France to rethink their training. One can only hope with state sponsored companies.