Airbus A320-family operators are being instructed to check angle-of-attack sensors on their fleets, after discovering that a manufacturing defect could result in the aircraft receiving incorrect data.
The European Aviation Safety Agency said that the fault, discovered during final assembly line tests, affects particular Thales angle-of-attack probes installed on all A320-family variants.
Incorrect removeal of machining oil during the manufacturing process means that oil residue could be present between the stator and rotor parts of the the angle-of-attack vane position resolvers.
This residue, said EASA, could become viscous at low temperatures, particularly in cruise, and affect the movement of the vane. "Multiple angle-of-attack probes could be simultaneously affected, providing incorrect indications of the angle-of-attack of the aeroplane," it added.
The problem was found when assembly line tests on two different aircraft revealed incorrect data.
Accurate data is critical because Airbus flight-control logic uses sensor information to prevent the aircraft reaching an attitude at which it could stall.
Erroneous angle-of-attack data, EASA said in a proposed directive on the matter, could result in "delayed or non-activation" of Airbus angle-of-attack protection systems.
EASA is to recommend identification and replacement of the Thales Avionics probes potentially affected within six months.
Source: Air Transport Intelligence news