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Ironies Following Aviation Accidents:

Johanna Ganthaler, an Itialian woman vacationing in Brazil, who missed AF447, caught another flight the following day and was killed in an automobile accident as she was driving home, when her car swerved into an oncoming truck in Kufstein, Austria.

Five passengers decided to miss BOAC 911 on March 5, 1966, which crashed with the loss of all aboard. Cubby Broccoli, Harry Saltzman, Ken Adam, Lewis Gilbert and Freddie Young were in Japan scouting locations for the James Bond film, You Only Live Twice. Source: Wikipedia, BOAC 911.

The Equatorial Mid-Atlantic is Known to be Stormy

Tradewinds flowing toward the equator form the Inter-Tropical Convergence Zone ("ITCZ"). Winds in the northern hemisphere flow toward the southwest, while winds in the southern hemisphere flow toward the northwest. During the northern hemisphere's winter months, the tradewinds come together, or converge, south of the equator. During the northern hemisphere's summer months, tradewind convergence occurs north of the equator. At the point of convergence, air is forced up, increasing convection, creating lines of rain and thunderstorms that can extend for hundreds of miles. As depicted below, these conditions were ocurring at the time of flight 447's loss. Get the current Atlantic Tropical Weather.

Image credit: Tim Vasquez, WeatherGraphics.com ©2009 - All rights reserved. Reproduced by permission. For a comprehensive analysis of the conditions probably encountered by Air France 447, see Tim's Air France Flight 447: A detailed meteorological analysis.

Depicted above is a radar simulation, based upon weather data in the mid-Atlantic, of the flight conditions probably being experienced by Air France 447. The flight proceeded northeast from the INTOL intersection, picking its way through an area of thunderstorms, several hundred miles wide, just north of the equator on its way to Paris. Its flight in the turbulent area probably lasted ten minutes. The aircraft was almost through the weather as it passed between two of the more powerful cells, or clusters of thunderstorm cells, when it stopped transmitting data.

Thunderstorms over warm water draw in a tremendous amount of most air, which can be lifted by rising air currents (updrafts) to great heights, sometimes exceeding 50,000'. Air France 447 was flying at FL350, or 35,000'. Did the flight encounter relatively warm (above -40 deg. C) super-saturated air, as it passed between the two areas of activity depicted? If so, did the relatively warm, moist air overcome the ability of one or more of the aircraft's pitot tubes, to remain ice free, resulting in conflicting data being sent to the air data computers?

Maintenance History

The U.S. Department of Transportation, Federal Aviation Administration (FAA) published an Airworthiness Directive (AD) on May 18, 2004, related to several Airbus models, including the A330. Although the Airbus is of European manfacture, and Air France is the French flag carrier, the FAA participates in regulatory oversight because Airbus jetliners serve cities in the United States, and are operated by a number of U.S. Airlines. The A330, in particular, is operated by US Airways and Northwest. Further note that the publication of an AD does not, of itself, necessarily send a negative message about any particular aircraft design. Airplanes, particularly jet transports, are complicated machines consisting of thousands of components. It would be more noteworthy to find and comment on a modern jet that does not have an AD issued, than to find one which has a number of ADs.

That said, here is the summary of the AD which pertains to the pitot tubes on the A330:

"This amendment adopts a new airworthiness directive (AD), applicable to certain Airbus Model A300-600, A310, A319, A320, A321, A330, and A340-200 and -300 series airplanes, that requires a one-time inspection to determine if certain Thales pitot probes are installed, a check for certain part numbers and serial numbers of the affected pitot probes, and cleaning of the drain hole of any affected pitot probes if obstructed. This action is necessary to prevent obstruction of the air intake of the pitot probes, which could result in misleading information being provided to the flightcrew. This action is intended to address the identified unsafe condition".

Note that this AD, issued five years ago, only requires inspection of the pitot tubes, so the cost of compliance is minimal:

"Cost Impact. We estimate that 758 airplanes of U.S. registry will be affected by this AD, that it will take about 2 work hours per airplane to do the inspection, and that the average labor rate is $65 per work hour. Based on these figures, the cost impact of the inspection required by this AD on U.S. operators is estimated to be $98,540, or $130 per airplane. [Emphasis added].

To read the full text of the AD, download the document here.

Another AD Required Replacement of the Pitot Tubes

Another AD (2004-03-33 Airbus: Amendment 39-13477. Docket 2001-NM-302-AD) required replacement, not just inspection, of the pitot tubes on larger variants of the A330 (the -300 series). Note that this AD calls for the installation of Thales pitot tubes. These are the pitot tubes that are the subject of the AF447 investigation. This AD references Airbus Service Bulletin A330-34-3038, dated November 19, 1996; or Revision 01, dated September 14, 2001; or Airbus Service Bulletin A330-34-3071, dated December 11, 1998; or Revision 01, dated May 30, 2001, depending upon the production modification of the aircraft. The summary of this AD includes the following warning:

"This proposal would require, among other actions, replacement of certain pitot probes with certain new pitot probes. This action is necessary to prevent loss or fluctuation of indicated airspeed, which could result in inadvertent excursions outside the normal flight envelope. This action is intended to address the identified unsafe condition".

The required maintenance procedure for A330-300 series aircraft is described, as follows:

"For Model A330-301, -321, -322, -341, and -342 Series Airplanes: Replacement of Rosemount Pitot Probes (g) Within 30 months after the effective date of this AD, do the action specified in paragraph (g)(1) or (g)(2) of this AD, as applicable.
(1) For Model A330-301, -321, -322, -341, and -342 series airplanes: Replace the Rosemount pitot probes in zones 121 and 122 with new Rosemount (formerly BF Goodrich) pitot probes, per the Accomplishment Instructions of Airbus Service Bulletin A330-34-3038, Revision 01, dated September 14, 2001. Replacements accomplished before the effective date of this AD per Airbus Service Bulletin A330-34-3038, dated November 19, 1996, are acceptable for compliance with the corresponding action required by this paragraph.
(2) For Model A330-301 series airplanes: Replace the Rosemount pitot probes in zones 121 and 122 with new Thales (formerly Sextant) pitot probes, per Airbus Service Bulletin A330-34-3071, Revision 01, dated May 30, 2001. Replacements accomplished before the effective date of this AD per the Accomplishment Instructions of Airbus Service Bulletin A330-34-3071, dated December 11, 1998, are acceptable for compliance with the corresponding action required by this paragraph".

Click here for the full text of this AD.

EASA Declines to Issue AD

On June 9, 2009, the European Aviation Safety Agency (EASA) issued Safety Information Bulletin SIB 2009-17 under the subject heading "Unreliable Airspeed Indication," wherein the agency acknowledged that, "There have been a number of occurrences of unreliable airspeed indications or misleading air data information". The bulletin explains that, "The root cause of this may be due to, but is not limited to, inappropriate maintenance, contamination by small objects or materials on the ground or in the air, extreme environmental conditions producing icing outside the certification envelope of the probes or large amount of water ingestion". Although EASA is empowered to issue airworthiness directives, the agency has, so far, addressed the loss of AF447 with a non-mandatory safety bulletin. The bulletin states that, "The Aircraft Flight Manuals and/or Flight Crew Operating Manuals include procedures for unreliable airspeed indication (Air data system misleading information) and these should be well known by flight crews". The only recommendation of this bulletin is that flight crews be trained, among other things, "To apply procedures for the safe continuation of a flight with unreliable airspeed indication up to a safe landing". The full text of EASA SIB 2009-17, as published nine days after the loss to AF447, has been saved here.

Similar Air-Data Anomalies Reported

Air Transport World (ATW Daily News Monday June 29, 2009) reported that the U.S. NTSB is investigating two incidents, one on May 21st and the other on June 23, 2009, during which airspeed and altitude information aboard Airbus A330 aircraft may have malfunctioned. The incident in June was described as, "The aircraft entered the cloud tops and experienced light to moderate turbulence. After about 15 sec. it encountered moderate rain that was visible on the windshield. The pilots noted that the cockpit suddenly became very warm and humid and a few seconds later all three airspeed indicators rolled back to 60 kt. and autopilots and autothrottles disengaged, as did rudder limit protection ..." In both of these incidents, the aircraft continued to a safe landing.

August 2009 Update: Europe Proposes Airworthiness Directive

On August 10, 2009, the European Aviation Safety Agency (EASA) issued notice of its proposal for an airworthiness directive, stating, "Occurrences have been reported on A330/340 family aeroplanes of airspeed indication discrepancies while flying at high altitudes in inclement weather conditions". If adopted, the airworthiness directive would require replacement of the Thales pitot tubes currently installed on the A330/340 fleet with another Thales pitot tube, which is believed to improve airspeed indication in heavy rain conditions. The full text of the proposal can be found here.

Underwater Search for Wreckage

Clues to help determine the cause of the crash are being sought by ships and submersibles in the mid-Atlantic. The New York Times on June 19, 2009 published an informative illustration depicting the sea floor and describing the search. The two most sought-after items: The flight data and cockpit voice recorders.

Summary

As of July 7, 2009, the flight data recorder and cockpit voice recorder have not been located. Because the 'pinging device' is only expected to last 30 days, and that time has expired without the recorders being found, it is likely that they will never be recovered. There are no witnesses, either from aboard or outside the aircraft. The accident reminds us of a bygone era, when an aircraft would depart and then, simply, be declared overdue and presumed lost. Were it not for the routine maintenance data automatically uploaded by the aircraft, we would have even fewer clues to the loss. Thankfully we have weather data from the mid-Atlantic Ocean, to correlate with the information uploaded by the aircraft. Our prayers for those lost and condolences to their families and loved ones.

About the Author

Dave Alden is a pilot for a U.S. Part 121 airline, and an attorney who practices aviation and bankruptcy law from offices in Sacramento, CA.

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