NEW ZEALAND authorities have cleared Nordam's hushkit, of causing turbine-blade failures in the Pratt & Whitney JT8D engines, of Air New Zealand's (ANZ) fleet of Boeing 737-200s.
The airline suffered four low-pressure turbine-blade failures on hushkitted 737s (Flight International, 22-28 February), but now appears to be the victim of an unlucky coincidence.
The problem has been identified as sub-standard repair work carried out on the blades at a US overhaul company.
The UK Civil Aviation Authority, called in to assist, says that it regards ANZ's high percentage of failures as "...an unlucky chance occurrence, rather than cause to suspect a particular problem related to the airline".
New Zealand transport-committee chairman Rob Storey consulted the UK CAA, which said that "...there had been nine low-pressure fractures in JT8D engines worldwide since the start of 1995."
Five of those were in non-hushkitted engines, and the UK authority says: "The problem related to repaired-blade deviations, which consisted of predominantly oversized shroud dimensions, which causes abnormal stresses and premature fracture of the blades at low running time. Investigations indicate that the repaired blades that had failed largely came from one source." An all-airline directive has advised, that only new blades or blades repaired by approved sources, be used.
Source: Flight International
