Operators of Pratt & Whitney PW2037 engines will have to increase inspection of second-stage high-pressure turbine (HPT) hubs if the FAA accepts two NTSB recommendations made Thursday. The safety calls follow an uncontained failure suffered by a Delta Air Lines Boeing 757 nearly three months ago.
Accident investigators issued an urgent recommendation Thursday that the FAA require all PW2037s be removed from service for inspection of the hubs at flight-hour and cycle thresholds “significantly” short of those achieved by the incident engine, which had logged 10,880 hours/4,392 cycles. They also recommended such engines be subject to continuing checks until the cause of, and corrective action for, previous cracking instances has been established.
The uncontained failure occurred to the right engine of a 757-232 operating as Delta Flight 624 as it began a takeoff roll at Las Vegas McCarran International Airport on August 6. The pilots reported hearing “a loud bang” and noted that the engine had lost power before they aborted the takeoff and returned to the departure gate, where all 166 passengers and four crewmembers disembarked. There was no fire or injuries.
A hole found in the bottom of the PW2037’s core cowl lined up with one through its HPT. Inspection also revealed “missing lugs” and cracks in the HPT hub. The NTSB subsequently learned that blade-retaining lugs in at least four other PW2037 second-stage HPT hubs have suffered cracks. Investigators report also that a routine overhaul of an American Airlines PW2037 had revealed cracks in two adjacent blade-retaining lugs in the relevant hub. The NTSB has requested information on all of these hubs.
The discoveries warrant immediate FAA action, according to NTSB acting chairman Mark Rosenker. “A string of consecutively fractured lugs could result in simultaneous release of multiple blades” exceeding the containment capacity of engine cases. The investigation is continuing.