History of Flight
On October 2, 2015, at about 0510 UTC, a Boeing 747-451 airplane, N662US, operated by Delta Air Lines as flight 158, experienced a loss of power from the No. 3 engine while in cruise flight at FL330. The flight was operating under 14 CFR Part 121 as an international passenger flight from Incheon International Airport (ICN), Seoul, Korea, to Detroit Metropolitan Wayne County Airport (DTW), Michigan. About 3 hours 40 minutes after takeoff from ICN, while in Russian airspace on the B241 airway near the GITRU navigation fix, the pilots reported hearing a loud bang followed by the No. 3 engine's N1 rpm decreasing and exhaust gas temperature (EGT) increasing. The pilots shut down the No. 3 engine, declared an emergency with Russian air traffic control, and requested a descent to FL290. After consulting with the dispatcher, they diverted to Tokyo-Narita International Airport (NRT), where they made a three-engine landing without further incident. The airplane was operating on an instrument flight rules flight plan.
Personnel Information
The captain, age 59, held an Air Transport Pilot certificate with ratings for airplane single-engine land, multi-engine land, and instrument. He was type-rated in the Boeing 747-400 as well as the Boeing 727, 737, 757, and 767. He held an FAA first-class medical certificate dated September 2, 2015, with no limitations. His most recent proficiency check was March 21, 2015. He had 10,617 total flight hours, with 4,449 hours on the Boeing 747-400 and 154 hours in the previous 90 days. He occupied the left seat as pilot monitoring. The first officer, age 58, held an Air Transport Pilot certificate with similar ratings and was type-rated in the Boeing 747-400. He held an FAA first-class medical certificate dated July 20, 2015, with no limitations. His most recent proficiency check was May 14, 2015. He had 9,683 total flight hours, with 5,628 hours on the Boeing 747-400 and 257 hours in the previous 90 days. He occupied the right seat as pilot flying.
Aircraft and Engine Information
The airplane was a Boeing 747-451, serial number 23720, registered N662US, and operated by Delta Air Lines. It was manufactured in 1988, originally delivered to Northwest Airlines, and acquired by Delta in the merger. The maximum takeoff gross weight was 873,000 pounds; the takeoff weight from ICN was 837,600 pounds, and the airplane was loaded with 49,120 gallons of fuel. At the time of the incident, the airplane had accumulated 109,167 flight hours. The No. 3 engine was a Pratt & Whitney PW4056, serial number P717530, with a takeoff thrust rating of 56,750 pounds. The engine had accumulated 94,778 hours and 11,814 cycles since new, with its last heavy maintenance in 2005 at Pratt & Whitney's Cheshire Engine Center. The low-pressure turbine (LPT) module, serial number D17579, had 95,180 hours and 11,623 cycles since new.
Flight Recorder Data
The digital flight data recorder (DFDR) was read out. The cockpit voice recorder was not removed because the incident event would have been overwritten by the time the airplane landed. DFDR data showed that during cruise at FL330, at around subframe reference number 170166, the No. 3 engine's EGT began to increase and fuel flow decreased while EPR and N2 remained steady. Subsequently, EPR dropped from 1.297 to 0.92 in two seconds, N2 decreased, and fuel flow surged briefly with no corresponding increase in rpm or EGT. Data from five previous flights showed comparable performance among all four engines.
Examination Findings
The No. 3 engine was removed and disassembled at Delta's Technical Operations Center under NTSB oversight. Disassembly revealed that one 3rd stage turbine vane cluster, number 29, was missing. A portion of its inner shroud was found in the engine. The remaining vane clusters were in place but heavily battered. Metallurgical examination of the inner shroud fragment showed remnants of fatigue on the counterclockwise side of the forward flange, with multiple origins and a maximum depth of 0.026 inches. The fracture surface beyond the fatigue was smeared, precluding determination of further progression. Wear patterns on the LPT case hooks were most extensive for the No. 29 cluster, and the inner transition duct showed wear consistent with the cluster having moved inward and aft. The LPT case had three small holes, the largest 0.69 by 0.44 inches, all under cooling air tubes that showed no impact damage. No damage was found inside the No. 3 engine nacelle, and no debris fell out when the cowling was opened. There was no fire damage.
Injuries and Damage
There were no reported injuries to the 4 pilots, 13 flight attendants, and 341 passengers. The airplane sustained minor damage, including nicks and dents to the underside of the right wing, inboard aileron, and leading edge of the right horizontal stabilizer. No other damage was reported.