investigators have concluded that insufficient bonding of ice-protection panels
in the engines of an Austrian Airlines Fokker 70 led to their breaking away,
impeding thrust and forcing the jet to make an emergency landing in a field
aircraft had been operating a service from Vienna to Munich
on 5 January last year, with 28 passengers and four crew members, when it
encountered icing conditions while descending to flight level 100 on approach to
the German airport.
air accident investigation agency BFU says that during the Fokker 70’s
prolonged operation in moderate icing conditions and with low engine thrust,
ice developed on the low-pressure compressor rotors of both Rolls-Royce Tay 620
panels on the engine – bonded into the intake of the engine and located between
the low-pressure compressor rotor and the outlet guide vanes – are designed to
protect the engine casing from ice falling from the rotor.
BFU says that shedding ice, as well as ice-induced vibration of the powerplants, caused the bonded
joints of these ice-impact panels to fail. It states: “Investigation of the
ice-impact panels and the associated bonding surfaces on the engines clearly
showed an adhesion failure.
means that neither the adhesive nor the materials to be bonded failed, but that
the bonding between the adhesive and the materials was insufficient. In this
case the reason for it could only be an insufficient preparation of the bonding
says that the engine fan case was “not prepared correctly” prior to the
adhesive being applied and that evidence shows that the bonded joints had
separated some time before. But it stresses that instructions for maintaining and repairing the
ice panels were unclear and difficult to follow.
the ice-impact panels in the Fokker 70’s engines had broken away, they became
trapped in front of the low-pressure compressor vanes, affecting the air-flow
in the bypass duct, and resulting in the engines only being able to generate
the aircraft descended towards Munich, the engine pressure ratio of the
left-hand powerplant fell
from 1.5 to 1.0 and, within 30sec, that of the right-hand engine also started
falling, dropping from 1.4 to 1.0 over a four-minute period – a reduction
which, say the investigators, was “independent of the thrust setting”.
this time the crew, concerned about earlier engine vibrations, had declared an
emergency and requested an immediate landing. But no warnings accompanied the
loss of thrust from the engines and the seriousness of situation did not become
fully apparent until the aircraft had descended to about 3,500ft, when the crew
noticed that the engine pressure ratio did not increase as the throttle levers
were pushed forward.
Realising that the aircraft was unable to
maintain the glideslope, the crew told air traffic controllers that they would not reach
the runway. The jet touched down at about
08:16, some 2.5nm short of Munich’s
runway 26L, with the landing-gear partially extended. It slid for 220m before
coming to rest, severely damaged, although none of the occupants was badly
has advised German civil aviation regulators that the installation and repair
procedures for ice-impact panels in the Tay
engines should be clarified, and ensure that these installations are such that
a failure will not lead to a significant loss of thrust from the powerplant.