Monday, June 08, 2009

The Air France Crash: More Questions Than Answers

The crash of Air France flight 447 from Rio de Janeiro to Paris on the last day of May is bad news for a number of reasons. The deaths of all 228 people on board make it the worst air disaster since 2001. And while advancing technology has enabled investigators to recover a limited amount of flight data through a remote data link that was operating at the time of the crash, the deep waters where the plane went down may prevent the recovery of the "black box" containing voice and detailed data recordings.

What do we know today, eight days after the crash? There were thunderstorms in the area that night, and early speculation centered on the possibility of a lightning strike to the plane. Although lightning hits planes hundreds of times a year, relatively little damage usually occurs and most modern aircraft can be considered essentially (though not totally) lightning-proof. Evidently, there was a satellite or other radio-mediated data link which was continually feeding certain types of flight data to the ground. Examination of this data shows that the flight speeds during the last minute or so of the flight became "incoherent," followed by a loss of cabin pressure and failure of electrical systems. While this information will be helpful in deciphering what went wrong, it apparently lacks the detail that flight data recorders can preserve. One can imagine a day when such radio links will take the place of, or at least duplicate, the capabilities of flight data recorders so that mechanical recovery of the black box will no longer be so urgent. The black box is designed to emit a sonar signal for 30 days after the crash, so the underwater recovery crews gearing up to find it are operating under tremendous time pressure, not to mention the water pressure at depths exceeding 20,000 feet. The box may never be found.

Recent news reports have focused on the fact that the plane's Pitot tube, the device that measures airspeed, had not yet been replaced with a newer model as the plane's manufacturer Airbus recommended. A Pitot tube is a small tube that faces directly into the airstream. The difference in pressure between the air inside the tube (which is blocked off and registers what is called "stagnation pressure") and the ambient or "static" air pressure, is an indication of airspeed, which is the most important kind of speed to know about when you are trying to fly a plane. These days, when most parts of a flight except for landing and takeoff are under automatic control, the airspeed data from the Pitot tube forms part of an elaborate computer-controlled feedback loop that maintains constant speed, altitude, and other flight characteristics.

The old saw about computers regarding "garbage in, garbage out" goes double when a feedback loop is involved. If enough ice forms on a Pitot tube to plug up the entrance, the indicated airspeed goes way below what is actually the case, and either the automatic pilot guns the engines inappropriately or the real pilots may take incorrect action based on faulty airspeed data. This is exactly what happened to an Argentine DC-9 flight in 1999, which resulted in a spectacular crash, killing all aboard.

Although I have no independent information on this, I hope that modern aircraft such as the Air France A330 that crashed have more than one means of measuring speed: either a second Pitot tube (which of course would be just as likely to ice up as the first one), or other means such as radar altimeter and speed measurements or GPS-based airspeed indicators. But whether the autopilot takes all these other inputs into consideration, and whether the real pilots do too, I don't know. Clearly, if the Pitot tube was involved in this crash, the right thing to do in the circumstances wasn't done.

All flight-critical Pitot tubes have heaters to prevent icing, but evidently the one on Flight 447 was deficient or non-optimal in some way, or else Airbus wouldn't have recommended replacing it. Of course replacements can be recommended for all kinds of reasons, some of which have nothing to do with safety. All that will come out in the investigation report, which will take months or more to complete.

Despite this crash, the general trend in air safety has been a positive one. More people fly every year, and so the safety record per passenger mile is even better than the raw statistics on crashes would indicate. But this record can be maintained only through the painstaking work of investigators, engineers, regulators, inspectors, and the pilots and crews who actually do the work. Most of the time the system works well, and the silver lining in every accident is the fact that it carries with it potential answers to problems that need to be addressed to improve safety even further. I just hope they are able to recover the flight data recorders in order to develop a complete picture of what went wrong, and to teach us how similar situations can be avoided in the future.

We will revisit this accident when more information is available, and in the meantime, our sympathy is with the relatives and friends of those who lost loved ones in this tragedy.

Sources: I drew on reports from Fox News at,2933,525117,00.html and an Associated Press report obtained from Yahoo News at, as well as the Wikipedia article "Pitot tube."


  1. For the last ten years there hasn’t been a technical reason why the digital flight recorder data isn't sent in real-time to the ground (see the BBC/Equinox video “The BOX”, 2000, on the flight recorders). During this ten year interval Boeing and Aerospatiale have had the capability of implementing remote aircraft flight recording. Using a remote aircraft flight recorder, with-in a couple of seconds, you have the planes position/location, its attitude, velocity, etc. safely stored on the ground and used for flight safety, aviation security and cost reduction. This data used in real-time could have also prevented 9/11 (see

    On June 4, 2009 the Los Angeles Times put this into their LETTERS section:

    “There is no technical reason why digital flight recorder data are not sent in real-time to the ground. We have the technology to do this. Then, within a couple of seconds, we would have a plane’s position, altitude and velocity safely stored on the ground. This information could be used for flight safety, aviation security and cost reduction. We don’t know what went wrong on Flight 447, but we would sure know where the plane went down, why it went down and possibly could have saved lives.”

    Telemetering the flight data to the ground in real-time would assure that we have the data - in many crashes the flight data isn't recovered (e.g. 9/11, et al) or has errors in it since no one is looking at it, or using it in real-time to find malfunctions.

    A year prior to 9/11 I spoke in NY at the International Aviation Safety Association meeting on preventing crashes like golfer Payne Stewart’s decompression crash. Nothing was done by the FAA or industry and we got 9/11 (hijacking is about ten percent of aviation fatalities) and the 2005, 100 fatality, Helios decompression crash. When a plane deviates from its approved flight plan we now have the ability to securely take remote control of it and land it safely at a designated airfield. We presently have remote pilot vehicles (RPVs) flying over Afghanistan that are controlled/piloted from continental United States (CONUS). Currently we are utilizing secure high bandwidth communication networks (for our RPVs, submarines, AWACS planes, etc.) and there isn't a logical reason for not making that technology available for cargo and carrier aircraft. The cost of 9/11 alone is ten times the cost of putting in a safe system and yet nothing has intentionally been done. We would now be accruing additional annual safety and cost benefits.

    Billions of dollars are wasted on unnecessary airport runway expansion programs to reduce fatal ground incursions. These incursions wouldn’t even occur if the flight data was shared so pilots and air traffic control had better visibility. But because the digital data isn’t shared automatically the pilot sees only a fraction of the information necessary to prevent a crash and the same hold for the air traffic controllers (ATCs). Crashes such as Tenerife (583 fatalities), Comair (49 fatalities), etc. are directly caused by the lack of visibility due to not sharing the DFDR, ATC and airport runway data in real-time. The real-time use and sharing of the DFDR data to prevent crashes is more important then its present post mortem autopsy mode of operation.

    This, Air France flight 447, is another example of horrific crashes that possibly could have been prevented and saved lives. We surely would be able to use the flight data to prevent recurring crashes of this type and to minimize the anguish of the passengers families and the cost and time of trying to recover the recorders. The data used in real-time: reduces the cost of flying; prevents recurring fatal crashes; prevents a host of fatal crashes that aren’t directly related to Air France Flight 447, and keeps our nation safe and secure.

    Sy Levine

    Remote Aircraft Flight Recorder and Advisory System (RAFT) patent #5,890,079, 3/30/1999

  2. In all kinds of vehicles also planes and choppers. Its better to check everything for the best precautions before drive it. Safety is really important, because you are carrying lives. So it is important to know everything in your vehicle before you drive it.