For more than two years, the disappearance of Air France Flight 447 over the mid-Atlantic in the early hours of June 1, 2009, remained one of aviation’s great mysteries. How could a technologically state-of-the art airliner simply vanish?With the wreckage and flight-data recorders lost beneath 2 miles of ocean, experts were forced to speculate using the only data available: a cryptic set of communications beamed automatically from the aircraft to the airline’s maintenance center in France. As PM found in our cover story about the crash, published two years ago this month, the data implied that the plane had fallen afoul of a technical problem—the icing up of air-speed sensors—which in conjunction with severe weather led to a complex “error chain” that ended in a crash and the loss of 228 lives.

The matter might have rested there, were it not for the remarkable recovery of AF447’s black boxes this past April. Upon the analysis of their contents, the French accident investigation authority, the BEA, released a report in July that to a large extent verified the initial suppositions. An even fuller picture emerged with the publication of a book in French entitled Erreurs de Pilotage (volume 5), by pilot and aviation writer Jean-Pierre Otelli, which includes the full transcript of the pilots’ conversation.

We now understand that, indeed, AF447 passed into clouds associated with a large system of thunderstorms, its speed sensors became iced over, and the autopilot disengaged. In the ensuing confusion, the pilots lost control of the airplane because they reacted incorrectly to the loss of instrumentation and then seemed unable to comprehend the nature of the problems they had caused. Neither weather nor malfunction doomed AF447, nor a complex chain of error, but a simple but persistent mistake on the part of one of the pilots.

Human judgments, of course, are never made in a vacuum. Pilots are part of a complex system that can either increase or reduce the probability that they will make a mistake. After this accident, the million-dollar question is whether training, instrumentation, and cockpit procedures can be modified all around the world so that no one will ever make this mistake again—or whether the inclusion of the human element will always entail the possibility of a catastrophic outcome. After all, the men who crashed AF447 were three highly trained pilots flying for one of the most prestigious fleets in the world. If they could fly a perfectly good plane into the ocean, then what airline could plausibly say, “Our pilots would never do that”?

Here is a synopsis of what occurred during the course of the doomed airliner’s final few minutes.


At 1h 36m, the flight enters the outer extremities of a tropical storm system. Unlike other planes’ crews flying through the region, AF447’s flight crew has not changed the route to avoid the worst of the storms. The outside temperature is much warmer than forecast, preventing the still fuel-heavy aircraft from flying higher to avoid the effects of the weather. Instead, it ploughs into a layer of clouds.

At 1h51m, the cockpit becomes illuminated by a strange electrical phenomenon. The co-pilot in the right-hand seat, an inexperienced 32-year-old named Pierre-Cédric Bonin, asks, “What’s that?” The captain, Marc Dubois, a veteran with more than 11,000 hours of flight time, tells him it is St. Elmo’s fire, a phenomenon often found with thunderstorms at these latitudes.

At approximately 2 am, the other co-pilot, David Robert, returns to the cockpit after a rest break. At 37, Robert is both older and more experienced than Bonin, with more than double his colleague’s total flight hours. The head pilot gets up and gives him the left-hand seat. Despite the gap in seniority and experience, the captain leaves Bonin in charge of the controls.

At 2:02 am, the captain leaves the flight deck to take a nap. Within 15 minutes, everyone aboard the plane will be dead.]

02:03:44 (Bonin) La convergence inter tropicale… voilà, là on est dedans, entre ‘Salpu’ et ‘Tasil.’ Et puis, voilà, on est en plein dedans…
The inter-tropical convergence… look, we’re in it, between ‘Salpu’ and ‘Tasil.’ And then, look, we’re right in it…

The intertropical convergence, or ITC, is an area of consistently severe weather near the equator. As is often the case, it has spawned a string of very large thunderstorms, some of which stretch into the stratosphere. Unlike some of the other planes’s crews flying in the region this evening, the crew of AF447 has not studied the pattern of storms and requested a divergence around the area of most intense activity. (Salpu and Tasil are two air-traffic-position reporting points.)

02:05:55 (Robert) Oui, on va les appeler derrière… pour leur dire quand même parce que…
Yes, let’s call them in the back, to let them know…

Robert pushes the call button.

02:05:59 (flight attendant, heard on the intercom) Oui? Marilyn.
Yes? Marilyn.

02:06:04 (Bonin) Oui, Marilyn, c’est Pierre devant… Dis-moi, dans deux minutes, on devrait attaquer une zone où ça devrait bouger un peu plus que maintenant. Il faudrait vous méfier là.
Yes, Marilyn, it’s Pierre up front… Listen, in 2 minutes, we’re going to be getting into an area where things are going to be moving around a little bit more than now. You’ll want to take care.

02:06:13 (flight attendant) D’accord, on s’assoit alors?
Okay, we should sit down then?

02:06:15 (Bonin) Bon, je pense que ce serait pas mal… tu préviens les copains!
Well, I think that’s not a bad idea. Give your friends a heads-up.

02:06:18 (flight attendant) Ouais, OK, j’appelle les autres derrière. Merci beaucoup.
Yeah, okay, I’ll tell the others in the back. Thanks a lot.

02:06:19 (Bonin) Mais je te rappelle dès qu’on est sorti de là.
I’ll call you back as soon as we’re out of it.

02:06:20 (flight attendant) OK.

The two copilots discuss the unusually elevated external temperature, which has prevented them from climbing to their desired altitude, and express happiness that they are flying an Airbus 330, which has better performance at altitude than an Airbus 340.

02:06:50 (Bonin) Va pour les anti-ice. C’est toujours ça de pris.
Let’s go for the anti-icing system. It’s better than nothing.

Because they are flying through clouds, the pilots turn on the anti-icing system to try to keep ice off the flight surfaces; ice reduces the plane’s aerodynamic efficiency, weighs it down, and in extreme cases, can cause it to crash.

02:07:00 (Bonin) On est apparemment à la limite de la couche, ça devrait aller.
We seem to be at the end of the cloud layer, it might be okay.

In the meantime Robert has been examining the radar system and has found that it has not been set up in the correct mode. Changing the settings, he scrutinizes the radar map and realizes that they are headed directly toward an area of intense activity.

02:08:03 (Robert) Tu peux éventuellement le tirer un peu à gauche.
You can possibly pull it a little to the left.

02:08:05 (Bonin) Excuse-moi?
Sorry, what?

02:08:07 (Robert) Tu peux éventuellement prendre un peu à gauche. On est d’accord qu’on est en manuel, hein?
You can possibly pull it a little to the left. We’re agreed that we’re in manual, yeah?

Bonin wordlessly banks the plane to the left. Suddenly, a strange aroma, like an electrical transformer, floods the cockpit, and the temperature suddenly increases. At first, the younger pilot thinks that something is wrong with the air-conditioning system, but Robert assures him that the effect is from the severe weather in the vicinity. Bonin seems ill at ease. Then the sound of slipstream suddenly becomes louder. This, presumably, is due to the accumulation of ice crystals on the exterior of the fuselage. Bonin announces that he is going to reduce the speed of the aircraft, and asks Robert if he should turn on a feature that will prevent the jet engines from flaming out in the event of severe icing.

Just then an alarm sounds for 2.2 seconds, indicating that the autopilot is disconnecting. The cause is the fact that the plane’s pitot tubes, externally mounted sensors that determine air speed, have iced over, so the human pilots will now have to fly the plane by hand.

Note, however, that the plane has suffered no mechanical malfunction. Aside from the loss of airspeed indication, everything is working fine. Otelli reports that many airline pilots (and, indeed, he himself) subsequently flew a simulation of the flight from this point and were able to do so without any trouble. But neither Bonin nor Roberts has ever received training in how to deal with an unreliable airspeed indicator at cruise altitude, or in flying the airplane by hand under such conditions.

02:10:06 (Bonin) J’ai les commandes.
I have the controls.

02:10:07 (Robert) D’accord.

Perhaps spooked by everything that has unfolded over the past few minutes—the turbulence, the strange electrical phenomena, his colleague’s failure to route around the potentially dangerous storm—Bonin reacts irrationally. He pulls back on the side stick to put the airplane into a steep climb, despite having recently discussed the fact that the plane could not safely ascend due to the unusually high external temperature.

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.”

Almost as soon as Bonin pulls up into a climb, the plane’s computer reacts. A warning chime alerts the cockpit to the fact that they are leaving their programmed altitude. Then the stall warning sounds. This is a synthesized human voice that repeatedly calls out, “Stall!” in English, followed by a loud and intentionally annoying sound called a “cricket.” A stall is a potentially dangerous situation that can result from flying too slowly. At a critical speed, a wing suddenly becomes much less effective at generating lift, and a plane can plunge precipitously. All pilots are trained to push the controls forward when they’re at risk of a stall so the plane will dive and gain speed.

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.

02:10:07 (Robert) Qu’est-ce que c’est que ça?
What’s this?

02:10:15 (Bonin) On n’a pas une bonne… On n’a pas une bonne annonce de vitesse.
There’s no good… there’s no good speed indication.

02:10:16 (Robert) On a perdu les, les, les vitesses alors?
We’ve lost the, the, the speeds, then?

The plane is soon climbing at a blistering rate of 7000 feet per minute. While it is gaining altitude, it is losing speed, until it is crawling along at only 93 knots, a speed more typical of a small Cessna than an airliner. Robert notices Bonin’s error and tries to correct him.

02:10:27 (Robert) Faites attention à ta vitesse. Faites attention à ta vitesse.
Pay attention to your speed. Pay attention to your speed.

He is probably referring to the plane’s vertical speed. They are still climbing.

02:10:28 (Bonin) OK, OK, je redescends.
Okay, okay, I’m descending.

02:10:30 (Robert) Tu stabilises… 

02:10:31 (Bonin) Ouais.

02:10:31 (Robert) Tu redescends… On est en train de monter selon lui… Selon lui, tu montes, donc tu redescends.
Descend… It says we’re going up… It says we’re going up, so descend.

02:10:35 (Bonin) D’accord.

Thanks to the effects of the anti-icing system, one of the pitot tubes begins to work again. The cockpit displays once again show valid speed information.

02:10:36 (Robert) Redescends!

02:10:37 (Bonin) C’est parti, on redescend.
Here we go, we’re descending.

02:10:38 (Robert) Doucement!

Bonin eases the back pressure on the stick, and the plane gains speed as its climb becomes more shallow. It accelerates to 223 knots. The stall warning falls silent. For a moment, the co-pilots are in control of the airplane.

02:10:41(Bonin) On est en… ouais, on est en “climb.”
We’re… yeah, we’re in a climb.

Yet, still, Bonin does not lower the nose. Recognizing the urgency of the situation, Robert pushes a button to summon the captain.

02:10:49 (Robert) Putain, il est où… euh?
Damn it, where is he?