Tag Archives: Flight 447

What happened to Flight 447?

This isn’t exactly breaking news, PBS covered this last year but it’s amazing that simple $2500 pitot brought down one of the safest airliners on the market. 

Here is how the New York Time’s magazine explains the crash and disappearance of Flight 447.

Air France Airbus A330In the last four minutes before the crash, the airplane sent a series of 24 automatic fault messages to a maintenance center in France. Among these, the first to jump out at experts involved a part called the pitot probe. Pitots (pronounced PEE-toes) are small cylinders that sit outside the body of the plane to calculate airspeed. The cost of a pitot probe is not high — about $3,500 each for the model on Flight 447, which disappears in the $200 million cost of a plane — but their importance would be hard to overstate. Without them, a plane’s flight computer has no way to determine speed, and the automatic pilot shuts down. That means that if any of the pitot probes, sticking out into the wind, happen to get clogged with dirt or ice, the plane will suddenly revert to manual control, forcing pilots to take the stick of a half-million-pound aircraft in whatever conditions disrupted the pitot in the first place.

In theory, this shouldn’t cause a crash. The probes can be compared to a speedometer in a car: steady on the gas, and you’ll be fine. Pilots are trained to respond to pitot failure by maintaining pitch and thrust until the probes resume working. Most of the time, they do.

But during the period of manual control, the margin of error is thin. For a passenger jet like the A330, the ideal cruising speed is about 560 miles per hour. If you go much faster, the center of lift moves back on the wing, pushing the nose down and increasing velocity, until you soon approach the speed of sound. At that point, shockwaves develop on the wings, interrupting the flow of air and reducing lift. The nose of the plane then gets forced into a dive that the pilot may not be able to pull out of. Then again, if you go too slow, the airplane stalls and falls. A plane must maintain a minimum speed to generate lift, and the higher it travels, the faster it must go. At 35,000 feet, the gap between too fast and too slow narrows ever closer. Pilots call it coffin corner.

This is where it gets unnerving.  Air France and Airbus knew the problem existed in the part but they decided not to replace the pitot’s with an upgraded version.  Again, it’s only a $2500 part.

Looking over the recent history of pitot failure can be unnerving. Peter Goelz, the former N.T.S.B. director, recalled several episodes during his tenure, but one in particular stood out: the crash of Birgenair Flight 301 in February 1996. “We had a Boeing 757 that had been on the ground in the Dominican Republic for a month,” he said. The investigation concluded that “during that time, one of the pitot probes got an insect nest built in it. Well, the crew took off and flew the plane right into the ocean.” All 189 people onboard died.

The pitot probes on Flight 447 were even more vulnerable than most in conditions like those at Tasil Point. They were produced by a French company, Thales, and the model was known as AA. In the years leading up to the crash of Flight 447, the Thales AA was problematic in places where the meteorological conditions do funny things with water. At high altitude and low temperatures, water sometimes doesn’t freeze. Instead, it hovers, but as soon as something solid — like a pitot tube — flies through it, the water flash-freezes to form ice. Until heaters can melt the ice, the pitot probes are out.

This could happen to any kind of pitot probe, but by the summer of 2009, the problem of icing on the Thales AA was known to be especially common. Why the probes were still in use is a contentious question, but here is what we know for sure: Between 2003 and 2008, there were at least 17 cases in which the Thales AA had problems on the Airbus A330 and its sister plane, the A340. In September 2007, Airbus issued a “service bulletin” suggesting that airlines replace the AA pitots with a newer model, the BA, which was said to work better in ice.

In response, Air France’s official policy was to replace the AA pitots on its A330 planes “only when a failure occurred.” In August 2008, executives at Air France asked Airbus for proof that the BA pitots worked better in ice, and faced with the question, Airbus conceded that it did not have proof. So it removed the claim from the service bulletin. Another five months passed.

During that time, another airline, Air Caraïbes, experienced two close calls with the Thales AA on its Airbus A330s. The company’s chief executive immediately ordered the part scrapped from the fleet and alerted European regulators, who then began asking questions. In their conversations with Airbus, regulators learned of the 17 cases of icing, and they also discovered, looking at those cases, that the failures seemed to be happening more often (9 of the 17 occured in 2008). None of the failures seemed to signal an immediate danger, so the Thales AA was not removed from service. Regulators simply asked Airbus to watch the problem and report back in a year.

It gets worse.

In private, some B.E.A. investigators agree that they have found things that disturb them. After the plane’s final communication, for example, it took nearly 11 hours for a search team to be sent to Tasil Point. For the first hour, air traffic controllers generated a “virtual flight” on their computers, as is common practice, passing the plane along its intended route. For the next two hours, controllers checked periodically to see if anyone had seen the plane, and when a controller in Brazil asked a controller in Senegal if the plane had reached Cape Verde, the controller in Senegal said that Cape Verde hadn’t talked to them but not to worry; so the controller in Brazil didn’t. By the time Air France alerted a satellite search-and-rescue, 4 hours and 20 minutes had passed, and then it was another two hours before anyone notified the B.E.A. A search team lifted off in Dakar 10 hours after the last radio contact and for the next 45 minutes flew toward Cape Verde, where they assumed the plane had gone down.

When I asked the director of the B.E.A., Jean-Paul Troadec, if this was a suitable response time, he practically jumped from his seat and cried: “No! It’s not! The alert should have been much more quick!” Yet the reports from Troadec’s office draw no such conclusion. When I asked another B.E.A. investigator, Olivier Ferrante, whether it is difficult to write the reports without pointing out mistakes, he acknowledged that it is a matter of craft. “This requires discipline in report writing,” he said. “For example, we don’t use the word ‘fault.’ We prefer to use the word ‘error,’ which has more proactive connotations.”

There does seem to be an incredible lack of transparency when it comes to airline maintenance and procedures.  If Air Canada or anyone isn’t keeping up with maintenance regulations and suggestions, shouldn’t that be public knowledge?  The NTSB website isn’t bad but it isn’t proactive.  How hard is it to list airlines who are compliant or non-compliant with the bulletins.  They can even explain why they aren’t compliant if you want to present both sides of the story but as an airline passenger, I want to know if the airline I am flying on is cutting corners when it comes to airplane maintenance.