Inadvertent deactivation of a pump during fuel transfer sparked the near-complete loss of thrust on a Dagestan Airlines Tupolev Tu-154 that forced the crew into an erratic emergency landing, during which the jet broke up.

Russia's Interstate Aviation Committee (MAK) examined several possible reasons - including contamination, starvation and presence of water - for the sudden onset of unstable fuel flow during the outbound climb from Moscow Vnukovo to Makhachkala on 4 December last year.

However, MAK concluded that the flight engineer accidentally switched off a boost pump while carrying out a manual transfer of fuel, 7min after take-off, as the aircraft climbed through 5,000m (16,400ft).

This transfer lasted 2min 50s but shortly after it started, as the aircraft reached 5,800m, the flight recorder registered initial "instability" in the fuel supply to the left and right-hand engines on the trijet, MAK said.

The fuel-burn showed "oscillations" in which the consumption fluctuated by about 600kg/h during a cycle of a few seconds.

After the transfer, the pilots noticed abnormal readings from the aircraft's altitude indicator and the engine instruments, before receiving a warning that the two outer engines on the Tu-154 were failing.

Flight-data recorder information shows the fuel consumption fluctuations intensified, and the crew opted to descend and reduce power. As they adjusted the thrust, similar fuel-burn oscillations started to emerge in the centre engine, although with a lower amplitude of 230kg/h.

The crew requested to return to Vnukovo but the crisis deepened as the electrical generators started to fail and, with only the centre engine functioning, the pilots opted instead to nurse the crippled aircraft to Domodedovo, about 85km north of its position.

While the landing was intended on Runway 32R, the aircraft was far to the right of the centreline on approach, 2min before reaching the airport.

It turned left, travelling almost perpendicular to the centreline, crossing the runway close to the threshold. The Tu-154 overflew the airport, 500m off the centreline, at about 60m before swinging right in a bid to line up with the runway.

By this point it was already 1,000m beyond the 32R threshold. The aircraft crossed the centreline again, at 13m height, before flying parallel to - but to the right of - the runway.

Its angle of attack increased to 22° and the jet descended rapidly, touching down heavily at a speed of 131kt, only 350m from the far end of the runway and 88m to the right of the centreline.

Flight 372 overran the end of the runway and broke up, killing two passengers, although another 169 occupants survived.

MAK, however, criticised the crew for failing to use all available resources to restore electrical power to the aircraft, and for not following emergency procedures for approach and landing with a double engine failure. It said the crew had not been adequately trained to handle the emergency.

Investigators found another 14 instances of similar events during the period between 1979 and 2010, several of which were the result of accidental deactivation of booster pumps.

Source: Flight International