Tiger Airways breached safety rules by failing to report a wing-flap problem on an Airbus A320s, a problem that reoccurred eight months later, forcing an unscheduled landing with 125 passengers on board.
In the second incident, a wing began flexing in a metre arc at 35,000 feet as crew tried to deal with the problem.
An Australian Transport Safety Bureau investigation found flawed manufacturing and intermittent computer glitches set the conditions for uncontrolled flapping of a wing aileron, or flap.
It found that recommended flap-control software fixes had not been installed on Tiger's aircraft at the time.
It further found that Airbus knew of uncontrolled flap movements due to faulty control valves, a problem the aircraft maker dealt with by publishing an instruction manual on the subject.
The safety bureau also found Tiger Airways breached the Transport Safety Investigation Act by failing to report the fault. Such faults have to be reported in case similar faults affect other aircraft of the same type.
Flight computers alerted the pilots to the impending problem on the Airbus A320 shortly after take-off from Mackay in Queensland, bound for Melbourne on May 18 last year, as it climbed past 1500 feet.
There was no apparent effect on the aircraft control, so pilots continued to climb to cruising altitude.
But at 35,000 feet the pilots felt a "light continuous shaking" from the aircraft.
A further examination of flight systems showed the left wing aileron, on the trailing edge of the wing, was flapping up and down "a couple of degrees".
But the situation worsened, and 10 minutes later, the aileron was flapping up and down by five degrees.
Pilots called the cabin manager to have a look out the window at the wing to see if there was any unusual movement going on. The cabin manager reported that the left wing was flexing up and down and the flap was not flush with the wing's surface.
Changing cruising speed did not solve the uncontrolled flapping, which the co-pilot could see was now causing the whole wing to flex up and down through an arc of one metre.
Now 40 minutes into the flight, the captain decided to divert and land at the Gold Coast. But things worsened further as the plane descended to 20,000 feet: the vibrations intensified, as did the aileron flapping and wing flexing.
Although not a recommended action, an Airbus quick-reference guide suggested turning the flap computer on and off to reset it, which the pilots did 15 minutes before landing, seemingly curing the problem.
Pilots landed the plane without further incident, but aircraft engineers on the ground, who examined the plane, could not find any fault or replicate it.
In Tiger's earlier incident of uncontrolled flapping, the plane returned to land after take-off. The fault cleared on landing and was noted but no action was taken - either in maintenance or in reporting it to the Australian Transport Safety Bureau.
Further investigation in Melbourne and France found the problem in the May flapping incident related to a bad adjustment and consequential premature wear of a main wing flap control mechanism, a so-called "aileron hydraulic servo" during the aircraft's manufacture.
Subsequent to the investigation, Tiger Airways has revised its safety incident reporting protocols, provided additional crew training and installed the recommended software fixes, the bureau said.
The manufacturer of the servo mechanism has revised its manufacturing processes to correctly adjust the mechanism.
Tiger Airways defended its handling of the matter, saying ‘‘while the symptoms of the two incidents were similar in nature, the incident causes are unrelated’’.
The airline said it felt no need to report the first occurrence as it ‘‘was not considered appropriate’’ based on what was known at the time, and safety was not at risk, but it reported the second incident ‘‘immediately’’ to the ATSB, a spokeswoman said.
‘‘Tiger Airways has a close working relationship with its regulators and implements regular flight crew training to ensure full compliance,’’ she said.
Read more at Aviation News http://www.smh.com.au
No comments:
Post a Comment