engine fault, in last month.
It had to return to Singapore after
dropping debris and suffering
damage to the left wing.
The aircraft was VH-OQA, or Nancy
Bird Walton, the first A380 delivered to
Qantas, entering service in 2008. It had recently undergone a scheduled heavy maintenance check.
No knowledgeable aerospace
commentator is implicating the
computerized systems that control the
A380.In fact, as we'll see later, the fly-
by-wire design will have helped the
crew safely land the damaged aircraft.
The engine was from the Rolls-Royce Trent 900 series. A high-bypass
turbofan design developing up to
80,000 lbf of thrust. It's only used in
the A380 by Lufthansa, Qantas and
Singapore Airlines. (Other A380
operators use Engine Alliance GP7000 engines, the product of a joint venture
between GE and Pratt & Whitney.)
Both Qantas and Singapore withdrew
all their A380s from service, to carry
out engine checks, as a response to
the accident and in accordance with
Rolls-Royce's recommendations.
Singapore re-introduced theirs earlier today, after checks showed no
problems, according to Flight International. Qantas expects to be finished before Monday.
The failure was in the #2 engine of this
four-engine aircraft -- the inboard of
the pair on the left wing. While it's not
yet known what went wrong with the
engine, the location of the damage to
the exterior engine casing is consistent with a failure in the high- energy section of the engine -- either of a turbine disk or the shaft on which it spins.
In other words, it's probably not, as
many have speculated, a fan blade
failure. The fans are further forward,
well away from the damaged area. Fan
blade failures are expected every so
often, and the engine casing is designed to contain any bits of flying
metal.
However, containment of a loose
turbine disk is a very different
proposition. A disk weighing 250lb,
spinning at, say, 12,000 RPM has far
too much kinetic energy to reliably
contain. Not without making the engine too heavy to use on an airliner,
anyway. Naturally, disk failures are not
at all common.
A recent European airworthiness
directive warned operators of a wear
problem with the engine's
intermediate-pressure turbine shaft, as noted by respected aviation journalist
Max Kingsley-Jones . However, an anonymous Airbus source quoted by
Jon Ostrower says that, "early
investigation is focusing on a part of
the engine that is farther forward in
the nacelle."
Fast-flying engine debris damaged
the wing. This caused problems with one of the redundant hydraulic
systems, as demonstrated by only half the spoilers deploying on landing.
Landing was also complicated by the
fact that only one engine thrust
reverser would have been operable.
This is because the aircraft only has
reversers on the two inboard engines,
and one of those was in bits on the ground.
However, presumably by
overstressing the braking system, the
pilots were able to bring the aircraft to
a safe stop, well within the length of
the runway.
Furthermore, it would appear that the
pilots were not able to shut down the
other left-hand engine (#1). In
pictures of the incident, the airport fire
service at Singapore can be seen
training their hoses on the #1 engine intake, which is blowing the water or
fire suppressant liquid out with
considerable force.
As Paul Cousins, the president of the
Australian Licensed Aircraft Engineers
Association, commented, the failure could have damaged the flight control
connections. A Full Authority Digital Engine Control (FADEC) computer,
located with its engine, will normally
detect the fact that it is no longer in
communication with the flight deck,
and will choose a failsafe operating
mode.
Assuming that both left-side engines
weren't producing significant thrust,
this would be an additional challenge
to pilots of a large, conventional four-
engined aircraft, such as the 747. Not
so in a fly-by-wire design; the flight management computers would
transparently compensate for the
asymmetric thrust produced by
engines #3 and #4.
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