Pitot Tube Design
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 manufacture, 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 prior to the accident, 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 041002.
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 Initially 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 of AF447, is here: easa_sib_2009-17. Approximately three monts later, EASA followed through, issuing AD 2009-0195 (summarized in the update on next page).