AIR FRANCE 447 THEORIES

Times, UK - Air France scrambled to replace pressure sensors on its A330 Airbuses yesterday after a pilots' union urged crew to boycott the long-range jets because faulty airspeed readings are suspected over last week's crash off Brazil.

"To prevent a repeat of this disaster we call on flight deck and cabin crew to refuse flights aboard the A330 and A340 series which have not been modified," said Alter, a union to which 10 per cent of the airline's crew belong. . .

"The first data from the doomed airliner reported a pitot failure and Air France has acknowledged that its jets had suffered several similar incidents. The Airbus went out of control as the electronic flight system failed after receiving conflicting airspeed readings via its three pitot tubes.

Pitot tubes have long been prone to blocking by ice, rain and insects. A failure in airspeed indication is a big handicap for a pilot but the aircraft can still be flown by hand with power settings and attitude, the orientation of the aircraft in relation to its flight direction. . .

Nearly 1,000 aircraft from the A330/340 series of long-haul airliners are in service. None had killed a passenger before. However, pilots and experts focused on what some see as a fatal chain of events that highlights flaws in the highly automated flight system on Airbus airliners.

In modern aircraft, particularly the ultra-automated Airbus family, pilots have less direct control. With defective computers in the heart of a tropical storm, the crew of the stricken Air France jet may have lacked the information to keep it flying.

The recovery of the aircraft's rudder has strengthened suspicions among some experts that the plane went out of control and broke up as a result of flying either too slowly or too quickly in severe turbulence.

Unsilent Generation - Parts of the tail appear intact; the tail looks like it was ripped off the plane at the points of attachment. . . To some observers, this bears a striking resemblance to the loss of the tail in the devastating American Airlines 587 crash in New York in November 2001. That plane was an Airbus 300. In an interesting comment on the Whatsupwiththat blog, a reader, Adoucette, writes:

"The disturbing thing to me is that the A330 design is derived from the A300. Both have composite tails. In the AA-587 crash in Nov of 2001, the NTSB blamed the failure of the A300's composite tail on the co-pilot. The NTSB claimed that the pilot made dramatic rudder inputs to counter wake turbulence from a 747 which had departed Kennedy two minutes earlier…. The NTSB said that the pilot, to combat mild turbulence, over controlled the aircraft by swinging the rudder fully to one side and then all the way to the other side, and it was this over-control which exceeded the tail's design limits. . . .

"Now if this is possible from rudder inputs in mild turbulence in clear air at relatively low airspeed over NY, consider what could happen at high speed in major turbulence over the Intertropical Convergence Zone, a storm-prone area where trade winds converge."

Also making its way around the web is a report from NASA's Langley Research Center on the possible effects of lightening on composite aircraft:

"Traditional aircraft act as Faraday cages when struck by lightning, which means that the charge stays on the exterior of the aircraft. However, as more aircraft are built using composite materials, we will need to understand the direct and indirect effects of lightning on those aircraft. The researchers at LaRC are studying the hazards of lightning on composite aircraft. Some of the issues include the fact that magnetic flux can penetrate avionics wiring, and that lightning damage is often more severe than tests would predict. Magnetic flux can penetrate composite aircraft more easily than metallic aircraft, inducing voltage and current on avionics wiring."