We received a report of an engine shutdown and turbine case burn-through, preceded by exceedance of the engine exhaust gas temperature (EGT) limit and loss of engine oil. Investigation revealed that the event was caused by damage to the HPT [high-pressure turbine] stage 2 nozzle due to inadequate part cooling. HPT stage 2 nozzles, part numbers (P/Ns) 2101M24G01, 2101M24G02, and 2101M24G03, are identified as having the inadequate cooling design. This condition, if not corrected, could result in HPT stage 2 nozzle failure, leading to uncontrolled fire, engine shutdown, and damage to the airplane.
As colleague Guy Norris noted, the Emirates incident probe quickly focused on the HPT Stage 2 nozzle area. Further investigation confirmed a second-stage HPT nozzle failure and "small holes and tears in the HPT case."
The FAA directive mandates repetitive checks of three specific part numbers and a permanent fix--installing guide vanes with improved cooling at the next engine shop visit--developed by Engine Alliance in 2011. As Norris reported, most operators have accomplished the work.
For engines that haven't been upgraded, initial checks are required before 1,500 total flight cycles, and repetitive checks must be done every 100 cycles thereafter. Nozzles found with burn holes must be swapped out immediately, at a cost of $487,000, according to FAA's directive.
The Emirates engine that shut down had 1,857 cycles, investigators report.