As a former Airbus A-320 Captain I have to admit that I take intense interest in the crash of the Air France Flight 447 A-330. The A-320 and A-330 are very similar in their systems and are quite often referred to as the “Big Bus” and the “Little Bus.“
It is well known in the Airbus fleet that Airbus has faced problems with the speed sensors on the A330 aircraft dating back to at least 2001, forcing changes in equipment as well as the pilot's flight manual. The automated error messages from the flight-deck pointing to discrepancies in airspeed data and other clues are hardly conclusive with regards to what led up to the problems on AF 447. France's chief crash investigator said on Saturday that airspeed problems had arisen on the same type of plane before but stressed it was too soon to say if these were to blame for the crash and added the plane was still safe to fly. Oh Really???
Airbus confirmed on Saturday it had recommended before the crash that airlines change speed sensors called pitot probes. But it said it was an optional move based only on performance rather than concerns about safety, which would be mandatory.
The A330 has three Air Data Inertial Reference Unit (ADIRU) systems and three pitot tubes. Although it is unlikely that all three would catastrophically fail at the same time if the aircraft inadvertantly entered an area of hail, all three of the sensors could be damaged nearly simultaneously. That being said, what kind of damage could have occurred and how much error would that induce in the system? Airbus does not say. Operators have been warned in the past of unsafe conditions resulting from potential ice damage to the sensitive pitot probes, and in 2001, France reported several cases of sudden fluctuation of A330 or A340 airspeed data during severe icing conditions, according to the U.S. Federal Aviation Administration. Specifically the FAA wrote in 2001 that "Lost or erroneous airspeed indications could result in lack of sufficient information for the flight crew to safely operate the airplane, and consequent inadvertent excursions outside the normal flight envelope.“
Pitot probes are small tubes sticking out from the side of the aircraft which resemble the nose of an ball-point-pen and provide the air pressure data to measure the speed of the aircraft. Their measurements can be erroneous or skewed if they become blocked, but that is normally the result of the pitot heating system failing and not impingement of ice or hail. A spokeswoman for Thales, which supplied the sensors on the crashed aircraft, said on Friday it was premature to speculation whether they were linked to the crash pending the investigation.
The French team leading the investigation into the Air France Flight 447 crash will have to work through a multitude of likely and less likely disaster scenarios including stormy conditions, faulty instruments, acts of terrorism, and the most difficult to assess will be possible flight computer malfunctions.
Air France CEO Pierre-Henry Gourgeon noted on Monday that immediately preceding AF447's disappearance, automatic messages sent by the plane indicated "multiple technical failures." Gourgeon said that the "succession of a dozen technical messages" sent by AF447 showed that "several electrical systems had broken down" immediately prior to the crash. The tough part about interpreting these messages is understanding the fault train that led to their transmission. Taken in various sequences those messages can lead to various theories about what caused them to be generated.
On Wednesday, TIME revisited an October 2008 incident in which a Qantas Airbus 330 went into an uncommanded 20-second nosedive, causing multiple injuries and requiring an emergency landing. One of the airplane’s three ADIRU’s began sending erroneous data spikes to the flight-control computer. The remaining two functioning ADIRUs should have taken over, but the computer acted on the false data and put the plane in a sharp dive. It was later learned that the same plane had experienced a similar occurrence in September 2006, as had three other flights. All those planes carried the same brand and model of ADIRU, as do more than one-third of the 330s and 340s in the Airbus fleet leading to the question, “So if this model of ADIRU has a history of failure, why does Airbus continue to fit them in its 330s and 340s?”
According to Airbus spokesman Justin Dubon, and as reported in the aviation trade magazine Air Transport News, manufacturer Northrop Grumman makes the ADIRUs for Qantas, and Honeywell for Air France. "There are no similarities in ADIRUs between the two cases," says Dubon.
The Airbus 330 is not the only Airbus product to suffer ADIRU failures. An Airworthiness Directive issued by the U.S. Federal Aviation Administration last year warned airlines of instances of failure in ADIRUs aboard Airbus 319, 320 and 321 models that "could result in loss of one source of critical altitude and airspeed data and reduce the ability of the flight crew to control the airplane." Dubon says these issues are "totally unrelated ... Our safety people have informed me that is not relevant to either the Qantas case or the Air France case."
What really concerns me is the flight recorders must be found. If they are not found, then all the analysis, even made by experts and professionals with all the time they need, will be very incomplete and based on a excessive interpretation. Without that conclusive information it is very likely that another A-330 will be lost for “undetermined reasons.”
