Death in the Atlantic The Last Four Minutes of Air France Flight 447


Part 2: Minute One: The Sensors Fail

It's hard to imagine a more precarious situation, even for pilots with nerves of steel: Flying through a violent thunderstorm that shakes the entire plane as the master warning lamp starts blinking on the instrument panel in front of you. An earsplitting alarm rings out, and a whole series of error messages suddenly flash up on the flight motor.

The crew immediately recognized that the three airspeed indicators all gave different readings. "A situation like that goes well a hundred times and badly once," says Arnoux, who flies an Airbus A320 himself.

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Photo Gallery: The Final Minutes of Flight 447

The responsible pilot now had very little time to choose the correct flight angle and the correct engine thrust. This is the only way he could be certain to keep flying on a stable course and maintain steady airflow across the wings if he didn't know the plane's actual speed. The co-pilot must therefore look up the two safe values in a table in the relevant handbook -- at least that's the theory.

"In practice, the plane is shaken about so badly that you have difficulty finding the right page in the handbook, let alone being able to decipher what it says," says Arnoux. "In situations like that, mistakes are impossible to rule out."

Danger of Icing Up

Aerospace experts have long known how dangerous it can be if the airspeed indicators fail because the pitot tubes ice up. In 1998, for example, a Lufthansa Airbus circling over Frankfurt Airport lost its airspeed indicator, and a potential tragedy was only averted when the ice melted as the plane descended. At the time, German air accident investigators at the German Federal Bureau of Aircraft Accident Investigation (BFU) in Braunschweig demanded that the specifications of the pitot tubes be changed to enable "unrestricted flight in severely icy conditions."

As early as 2005, the French aerospace company Thales, which manufactures the pitot tubes used on flight AF 447, set up a project group called Adeline to search for new technical solutions to the problem. According to a Thales document, loss of the airspeed indicators "could cause aircraft crashes, especially in cases in which the sensors ice up."

Aircraft manufacturer Airbus was well aware of the shortcomings of the Thales pitot tubes. An internal list kept by the airline manufacturer shows there were nine incidents involving them between May and October 2008 alone.

More than two months before the Air France crash, the issue had been raised at a meeting between Airbus and the European Aviation Safety Agency. However, the EASA decided against banning the particularly error-prone pitot tubes made by Thales.

In fact, the problem with the airspeed indicators lies far deeper. To this day, the relevant licensing bodies still only test pitot tubes down to temperatures of minus 40 degrees Celsius (minus 40 degrees Fahrenheit) and an altitude of about 9,000 meters (30,000 feet). These completely antiquated specifications date back to 1947 -- before the introduction of jet planes.

What's more, most of the incidents of recent years, including that involving the ill-fated flight AF 447, occurred at altitudes above 10,000 meters (33,000 feet).


Discuss this issue with other readers!
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vluthra1 02/25/2010
1. AF 447 Crash Analysis
Is the European Aviation Safety Agency (EASA) a sitting duck, when it comes to minding or controlling its own kith-kin AB? If faulty equipment can jeopardize hundreds of lives, why are they not being summoned into the European Courts of Justice for negligence in allowing unsafe equipment to be declared safe? And then comes the question of Pilot competence. As we fly, we entrust our lives with the men/women who command these birds. But do they know all, that they need to know, to do their job right? Are they somewhat like the doctors, who can actually test and try in real life situations?
globetrodden 02/26/2010
2. Not True
"...'But pilots are very reluctant to do something like that,' Hüttig adds. After all, it makes the flight more expensive, causes delays and is frowned upon by airline bosses. ... " That's nonsense. The idea that pilots would fly through a dangerous storm to avoid delays or diversions is preposterous and, to an airline pilot like myself, highly offensive. Patrick Smith Boston
nikosathens 02/26/2010
3. air speed measurement
I'm a simple engineer and not an aircraft specialist and I wonder why a whole sophisticated airplane computer system can crash because of malfunction of the pitot tubes that measure the aircraft velocity. Could the pilot not cross-check the speed by a reading from a GPS system?
michaeljohnwright 02/27/2010
4. Michael Wright
I am a private pilot, and on one occasion had a similar incident, though in a small aircraft. It was not caused by the pitot tube getting iced up, but by the static pressure vent. This vent is also required to measure airspeed, but is also vital for altitude and vertical speed indications. When not working, the outside air pressure and altitude readings freeze, vertical speed is shown as zero, and the altimeter shows continuing increases in airspeed when descending. It would naturally lead to reducing air speed as the pilot tried to stop the increase in indicated air speed. This could lead to a stall in a few tens of seconds. It is perfectly possible to fly an aircraft without an air speed indicator, using a combination of vertical speed indication or altitude indication together with power setting.
oppen2 02/27/2010
5. Two points
An interesting and relatively thorough update on this crash, given the space available. An editor should have, though, caught two journalistic missteps: 1. "As a consequence, it was probably the plane's third pilot, Pierre-Cédric Bonin, a dashing amateur yachtsman, who steered the aircraft to its doom." Terribly unfair, with its implication that the senior pilot left the flight deck in the hands of an unqualified amateur. In his personal life, Bonin may have been dashing and enjoyed sailing. But he didn't arrive in the cockpit of a large jet with a major carrier without thousands of hours of experience and more stringent checks and rechecks of his ability than most of us will ever face in our professional lives. There is no evidence presented in the article that another pilot could have more successful in trying to recover control of the airplane. 2. "For several years now, Airbus has offered its customers a special safety program - called "Buss" -- at a cost of €300,000 per aircraft. If the airspeed indicator fails, this software shows pilots the angle at which they must point the plane. "Up to now, Air France has chosen not to invest in this optional extra for its fleet." Placement makes all the difference. Had these two paragraphs been in the main body of the story, they're relevant pieces of information. Placing them as the penultimate and then final paragraph is a journalistic trick to leave the reader with the somber conclusion that if only Air France had purchased this relatively inexpensive software, the accident would never have happened. Had the equipment been installed, many questions remain. The most obvious: Would it have functioned properly with the shutdown of the flight computer? The writer could have indicated how many other airlines purchase the optional software. And the obvious question not posed or answered: If the software is that important to the safe operation of the plane, why is it optional?
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