The European Aviation Safety Agency has issued the first airworthiness directive relating to the Airbus A380, mandating checks for cracking of vanes in Rolls-Royce Trent 900 high-pressure turbines.
The directive states that development testing and flight tests of the Trent 900 have revealed evidence of cracking on some nozzle guide vane surfaces.
EASA says that not all nozzle guide vane assemblies are affected and that the problem would become apparent on affected engines within 1,000 cycles.
"Analysis of test data and review of the manufacturing process has revealed compounding effects that may contribute to a shortfall in component life and an increased likelihood of premature cracking in this region," it states.
Excessive cracking on the vanes' convex surface could, it says, lead to possible fracture of high-pressure turbine blades - and subsequent engine damage - if vane material is released. Turbine gas flow could also be blocked, it adds.
R-R says that "a modification was introduced to the cooling of the Trent 900 nozzle guide vanes just over a year ago to resolve the potential issue on the early entry into service Trent 900s, although no NGVs have failed in service". It adds: "The modification has now been rolled out on a number of early in-service engines and the remainder of the fleet will be modified as required, as part of the maintenance programme. No new-build Trent 900s are affected."
EASA is instructing operators of Trent 900 engines to inspect the nozzle guide vane surfaces before 400 cycles, and to repeat these inspections at least every 100 cycles. If no damage is detected by 1,000 cycles, it adds, normal inspection maintenance can be resumed. The directive takes effect from 2 December.
Source: Flight International
