Saturday, May 28, 2011

Initial Findings on Air France Flight 447

It has been almost two long years since I last posted on this blog. Many things have happened since then. However, this blog still lives and will continue to provide a bit of aviation history. Yesterday, the French accident investigation bureau (BEA) announced their initial findings on the crash of Air France flight 447 over the Atlantic Ocean in 2009. This came about after a salvage operation found the wreckage in 2011. The Airbus A330-200 was flying in nasty weather at the time of the crash. The findings today coincide with a theory many pilots and aviation analysts have long predicted the failure of the pitot tubes. Now the findings show that the pilots had faulty speed-readings that led to a loss of speed and an unrecoverable stall. This meant that the aircraft was flying too slow to provide lift on its wings and lost the ability to fly. An aircraft flies not from the wind that pushed below the wing, but the wind that pulls the aircraft above the wing (also known as the Bernoulli principle).


Example of a disruption of lift over the aircraft's wings.

But the mystery of Flight 447 goes deeper because the aircraft fell from 35,000 feet and crashed on its belly into the ocean. Stall recovery is one of the basic lessons pilots learn. In order to get lift again, the aircraft has to dive in order to gain speed and air above its wings. However, the initial findings show that the pilots did the opposite and pulled up. The action by the Air France pilots coincides with the most recent accident in the United States of America. In February 12, 2009, Colgan Air Flight 3407 crashed in the suburbs of Buffalo, New York. The aircraft was beginning to stall upon landing and the pilots pulled up, ensuring a stall would happen. The pilots, however, were responding to the aircraft automatically diving (a stall protection commonly found on modern airliners) so close to the ground and over-corrected. The problem with Colgan Air Flight 3407 was the safety failures of regional airlines in ensuring that their pilots are fully rested and apt to fly the aircraft. Pilot fatigue could have also played a part in the crash of Flight 447. There is still little information published by the BEA and it is too soon in their investigation to conclude, or rule out, to any failure. But the problem is that the pilots in Flight 447 were not rookies. These pilots climbed up the career ladder flying various airliners in order to become A330 pilots. It seems unreasonable that seasoned copilots would commit such an error in recovering from a stall.
Another issue is why Air France Flight 447 stalled in the first place. The reports state a failure on the pitot tubes during flight. Pitot tubes are small pressure tubes that absorb air and measure the airspeed of an aircraft. You might have seen the pitot tubes as an aircraft's 'whiskers.'



A Boeing 737's 'whiskers.'

Each aircraft carries at least two pitot tubes, one for each pilot and another working as backup. An aircraft does not crash because of a pitot tube failure, but by actions on the pilot and/or aircraft computers resulting from that failure. On February 6, 1996, Birgenair flight 301 crashed when a hornet made a nest in one of the pitot tubes. The difference between the measurements from the failed pitot tubes and functioning pitot tubes confused the aircraft computer, sending it into a frenzy that then confused the pilots when the aircraft entered into an unrecoverable stall. On October 2, 1996, AeroperĂș Flight 603 had problems with the altitude measurements as soon as it took off. The computers sounded off alarms when it was unable to read the correct altitude, vertical speed, and airspeed. While trying to fly back to the airport in Lima, Peru, the aircraft struck one of its wingtips with the Pacific Ocean. The pilots were unable to recover the aircraft and it crashed twenty seconds after the wingtip strike. The problem was that the maintenance crews put masking tape over the static ports (part of the system connected to the pitot tube that measures altitude, airspeed, and vertical speed) during cleaning and forgot to remove the tape.
The initial findings on the accident state that the pitot tubes accumulated ice when it entered into the storm. The clouds in a storm look fluffy because of the dense amount of humidity within the clouds. These storm clouds have wind swiftly fly from the ground toward the sky, cooling the humidity in the clouds. This creates raindrops and ice at higher altitudes. The pitot tubes have heaters that melt the ice from building up within the tubes. Storms, however, generate too much ice to build up in the pitot tubes. The problem with Flight 447 was that there was a massive storm, hundreds of miles wide, blocking their flight toward Europe. Despite other flights safely flying through the storm, Flight 447 crashed in it.
The French government partially owns Airbus. This is why there is sneaking suspicion in BEA's haste to blame the pilots. Airbus designs their planes to fly on computers and sensors, relegating the pilot as a backup in case technology fails. This has caused a horrific scandal before. During the demonstration flight of the A320, the aircraft followed its autopilot in flying level...into the forest.


http://www.youtube.com/watch?v=bzD4tIvPHwE
Kudos on the ironic message in the video commentary.

That was Air France flight 296. Both Airbus and the pilots were to blame in flight 296. The pilots came in too high and too fast and did not make a flyover to get familiar with the airport and its surroundings. However, Air France pressured the pilots to arrive at a certain time in an airport that was not familiar to the pilots. Airbus was at fault because they had a faulty auto throttle (the autopilot mechanism controlling the engine power) and the altitude measurements were not efficient. This is why the aircraft was flying too slow (not the angle of attack - the way the nose is pitched up high) and the engines went into full power after the aircraft dove into the forest. Despite only losing 3 lives in an aircraft with 136 people onboard, the penalties were harsh. The French government sided with Air France and Airbus and placed full blame on the pilot. The French courts convicted Captain Asseline and the rest of the crew of involuntary manslaughter, with the Captain serving time in prison. The stakes for Airbus is high as a failure in its computer system scares away passengers and clients. The latter is more frightening to Airbus because these clients can easily buy aircraft from its main competitor, the Boeing Company
The initial findings do not cover all of the factors leading to the crash of Air France 447. Nonetheless, Airbus already ordered all A330 owners to replace their pitot tubes and problems with the A330 are now being addressed. The most important thing about investigating air crashes is to find all of the flaws that caused the accident and fix them. This is one of the principle ways that flight becomes a safer way to travel.


Photo Credits:
Deep Stall image: Wikipedia http://en.wikipedia.org/wiki/File:Deep_stall.svg
Southwest Boeing 737 images: Airliners.net http://www.airliners.net/photo/Southwest-Airlines/Boeing-737-3H4/1264077/L/&sid=569ca01fd21e5d382495cbdc4672b46c and http://www.airliners.net/photo/Southwest-Airlines/Boeing-737-3H4/0048011/L/&sid=569ca01fd21e5d382495cbdc4672b46c
Air France Flight 296 crash video: Youtube http://www.youtube.com/watch?v=bzD4tIvPHwE
Air France Flight 296 image: Airdisaster.com http://www.airdisaster.com/photos/af296/2.shtml

2 comments:

  1. Thanks for your history on these pitot tube failures. I have see all the "Air Crash Investigation" stories, including the episode about the convicted Captain Asseline, and am shocked that the problems with Pitot tube failures have not been properly addressed (where conflicting Pitot tube data causes computer malfunctions). I did not realize, however, that the French government partially owned Airbus, a fact which certainly explains the aggressive conviction of Captain Asseline. But since the hornet's next incident 16 years ago, and the later incident with the 'taped' tubes, it is criminal that a reliable solution has never been implemented.

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    1. Sorry to get back so late. I am glad that you learned a lot from this post. I also agree that it is reprehensible that major repairs have not gone on until this accident. This is one of the reasons why one writer, Andrew Weir, wrote about the 'Tombstone Imperative' and the lack of safety changes by governments until forced to do so in light of a deadly accident.

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