The FAA issued an airworthiness directive (AD), requiring repetitive ultrasonic inspections of the fan mid- shafts of all -1B and -2Bs. The AD was also introduced following the discovery of a cracked shaft on a second -1B during the inspections. It adds the “root cause is still under investigation, but the failure of the FMS is likely due to environmentally assisted cracking; a type of corrosive cracking that is time- dependent.”
Further investigations of the 747-8 engine anomoly then revealed that the -2B's FMS was not broken and that damage was limited to the LPT.
The NTSB, which was leading the Shanghai investigation with the Chinese aviation authority CAAC, then issued a statement to correct the impression the two were linked. It says “the preliminary examination of the engine revealed damage that was primarily limited to the LPT hardware at the rear of the engine. Aside from minor collateral damage, the engine hardware forward of the LPT (including the neighboring high-pressure turbine) does not exhibit damage.”
The NTSB also adds “there was no indication of damage to the fan mid-shaft. We are continuing to work with the CAAC and GE to determine the reason for these observations.”
GE then issued a service bulletin on Oct. 3, calling for -1B and -2B operators to do a one-time, fleet-wide borescope inspection of the LPT stage-one static nozzles—which direct air into the rotating blades—to ensure they are properly installed. The investigation seems to indicate that a misassembled LPT stage-one nozzle was the culprit.
In the meantime, Qatar Airways CEO Akbar Al-Baker was quoted by Reuters on Oct. 1 as threatening to further delay formal acceptance of his airline's first 787 until the new aircraft ready for delivery receive the new coating. By Oct. 3, however, it appeared this threat was an empty one, and preparations were underway for an expected delivery ceremony in mid-October. Qatar's 787 deliveries were originally expected to begin earlier in the summer but were delayed by issues with integration of the inflight entertainment system.