Let me start by saying categorically that I am not
pointing any fingers in this post. I am just highlighting a concern that we
might, as an industry, have taken our collective eye off the ball when it comes
to managing the operational safety of our aircraft.
Last week I read on twitter that an Airbus A330
had encountered an airspeed discrepancy between left and right instruments
during take-off at Brisbane airport. The pilots correctly abandoned the
take-off as they were still below decision speed V1, and returned to the
parking stand for maintenance investigation. The engineers did something with
the air data computers, which process raw air data into information for the
instruments. I forget what they did - re-racked or swapped them I think - and
selected one unit off in accordance with the minimum equipment list (MEL). The
aircraft was then dispatched. After getting airborne the crew again observed an
airspeed discrepancy and returned to land.
Less than 2 years ago an Airbus A320 suddenly
disappeared from ATC radar, after apparently making a very rapid climb above
the cleared cruising level and then plummeting into the sea below. There was
much speculation that the flight had encountered severe turbulence or icing and
the pilots had been unable to maintain control.
In the first case it was found that mud wasps had
started to build a nest in one pitot probe during the 2 hour stopover prior to
the first take-off attempt but apparently no-one had thought to look into the
probe for obstructions. Instead they went straight for a technological fix. In
the second case the investigation found that, in an attempt to rectify a
recurring fault with the rudder travel limiter, the captain pulled and reset the
circuit breakers for both flight augmentation computers (FAC), contrary to
abnormal procedures. The aircraft’s flight control logic immediately reverted
from ‘normal law’ to ‘alternate law’, the autopilot disengaged and much of the automatic
flight envelope protection was lost. The aircraft was manually flown into a
steep climb and stalled – it never recovered.
It feels to me like we may have forgotten the
basics of how our aircraft work…
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