A pilots union called on Air France crew today to refuse to fly long-range Airbus jets until the airline replaced unreliable speed sensors that are believed to have led to the crash of Flight 447 off Brazil last week.
“To prevent a repeat of this disaster . . . we call on flight deck and cabin crew to refuse all 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.
Brazilian searchers have so far retrieved the bodies of 24 of the 228 on board the Airbus A330 that came down in the Atlantic 600 miles off northeast Brazil. Submarines are now hunting for signals from the black box flight recorders that lie on the ocean floor.
The recovery yesterday of the aircraft’s vertical tail has strengthened suspicions among experts that the aircraft went out of control and broke up as a result of flying either too slowly or too fast in severe turbulence on its flight from Rio to Paris on June 1.
Air France promised this morning to complete the replacement within days of all pitot tubes — external speed sensors — on its 35 long-haul Airbuses. No flights were cancelled and other pilots’ unions said that they did not plan to boycott the aircraft.
Alter accused the airline of covering up its actions over the airspeed problem. The charge added to pressure on the airline and the Toulouse-based Airbus company to explain why it had not taken faster action to remedy equipment that its pilots were told was potentially dangerous last November.
In a November 6 circular to pilots that surfaced yesterday, Air France reported “a significant number of incidents” in which false speed readings had upset the computerised flight system — in exactly the way that appears to have happened on Flight 447.
These incidents, from which the crew were able to recover, had occurred at cruising altitude in zones of turbulence and freezing conditions, it said. As a result of the false readings — apparently caused by ice in the pitot tubes — the automatic pilot disconnected. Four minutes of data messages from the doomed Airbus last week reported the same sequence but the pilots were unable to regain control.
Airbus had been in discussion with its client airlines about unreliable pitot probes for several years and was recommending their replacement. The replacement was not mandated by any authority as an auronautical directive (AD).
Airline executives and aviation experts cautioned against haste in attributing blame for the crash, especially since the only evidence comes from the sequence of 24 messages from the aircraf’ts final four-minutes.
Tim Clark, the president of Emirates Airlines, which has a fleet of 29 A330-200 planes, said: “It is a very robust airplane. It has been flying for many years, clocking hundreds of millions of hours and there is absolutely no reason why there should be any question over this plane. It is one of the best flying today.”
However pilots and experts focused on what many saw as a fatal chain of events that exposes flaws in the highly automated flight system of the Airbus family of airliners.
Pitot tubes have been prone to blocking since they were invented in the early 18th century by Henri Pitot, a French engineer, to measure the speed of gasses or fluids. 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 direction of flight.
In modern aircraft with advanced electronics, and particularly the ultra-automated Airbus family, pilots have less direct control over the aircraft.
The crew of the stricken Air France plane would have had to take over from a computer that was in the throws of the equivalent of a cerebral haemorrhage. In the heart of a storm, they may have lacked the information to keep the big jet flying upright in the narrow”envelope” of high altitude speed limits known as “coffin corner”. Their margin of safety could have been as little as 60-80mph, beyond which the aircraft would stall or dive, an Airbus pilot said.
Speculation over the Airbus systems and the crew’s likely response is filling the internet forums where aviation professionals gather.
One Airbus captain wrote on one site today: “I have never been taught unusual attitude recovery in the simulator. I was told that you don’t have to have this training, because the Airbus has so many protections, that you don’t need this skill (sounds very similar about the reasoning behind Titanic) . . .”
Another pilot wrote: “The automatics make life easier on the Airbus but the failure states are far more complicated and less intuitive than on a Boeing.”
Source:The times
search the web
Custom Search
