Wednesday, June 3, 2009


Air France Flight 447 is down. Sadly, it is expected that all 228 aboard are lost. The earmarks are all too familiar. Severe weather and a loss of radar contact usually mean in-flight break-up and rapid descent. This would, of course, explain the lack of a distress call and automatic reporting of electrical failure and significant turbulence by the onboard real time condition reporting system.

The aircraft went down in an area called the Intertropical Convergence Zone (see picture above). This is an area where the Northern and Southern hemisphere winds and weather collide to make a perfect condition for severe convective weather. That means severe thunderstorms frequently exceeding 50,000 feet with damaging turbulence, hail, intense rainfall and lightning. On the night of the crash, this area was especially hot with thousands of miles of severe weather making circumnavigation impractical.

Therefore, the only way to get from Rio to Paris was to penetrate this band of severe weather, a daunting task for even the best aircrews flying the most sophisticated airliner. There is no coincidence that shortly after entering this area of severe weather the aircraft was lost. Whether it was due to an encounter with severe turbulence or a lightning strike that exploded a fuel tank can best be determined when the wreckage is found, and surely it will be one day.

The cockpit voice and flight data recorders will also be very helpful but the automatically transmitted data already portends the turbulence, electrical anomalies and tragic end. This is why cockpit voice and flight data recorder information should be transmitted real time to home base.

Coincidentally, an Airworthiness Directive had been issued in 2005 by the French authorities requiring float valve changes in the trim fuel tanks of this aircraft model’s horizontal stabilizers. The purpose was to avoid lightning or static electricity setting off an explosion in those tanks. The compliance time was quite lengthy and, while this aircraft was built in 2005, it is not clear whether it had the benefit of the improved floats. If it didn’t, or the fix was ineffective, a lightning strike on the trim tanks could have been a catastrophe that even the best crew would have been unable to avoid.

It is, therefore, quite possible that the old problem of airliner exploding fuel tanks has reared its ugly head again. While better fuel tank standards have been published and bantered about the industry and governments since TWA 800 exploded in 1996, none of the legacy airplanes have benefited from the new standards and this Airworthiness Directive, which aimed to chip away at the problem.

Aircraft radars have come a long way, providing flight crews with far better weather avoidance information than ever before. Unfortunately, weather avoidance is not weather penetration, but the demands of airline flying and schedules often blur the difference.

Avoidance means not going there, penetration means getting into it and avoiding the damaging weather by skillful use of the radar. The letter works most of the time but not always. Aircraft and human graveyards are full of the results of severe weather penetrations because there are limits on even the best radars. Intense rainfall absorbs signal strength and confuses returns, intense cells hide others just behind and give a false sense of security that safety is just a few miles away, when the worst may be yet to come.

Last year a computer failure pitched an identical aircraft so violently, the crew thought there was a clear air turbulence encounter. The manufacturer said it was impossible and could not have occurred. Later it appeared that indeed the impossible could happen. One out of many computers could cause a dangerous and sudden pitch excursion that might have led to structural failure. That must be ruled out in this case. While turbulence may have been the initiator, computer failure may have increased its lethality.

No one wants an accident. No one deliberately tempts an accident with a planeload of families in the back and pilots who likewise want to get home alive up front. Indeed, they are the first to go. But whether this accident is the result of mechanical failure, the failure to simply remain on the ground in the face of impassable weather or the unlikely act of a saboteur, it is nonetheless the worst of nightmares come true.

Weather. Mechnical failure. Equipment malfunction. It looks like any one of these may have played a role. Whatever the ultimate cause, with today’s technology there is no reason for an airliner accident. With the prospect that this single field of human endeavor may one day be accident free, these deaths must not be in vain.

Arthur Alan Wolk
June 3, 2009

Watch Wolk discuss the crash on MSNBC