History of Flight
On June 7, 2017, at about 0950 universal coordinated time, Delta Air Lines flight 276, a Boeing 747-451 airplane (registration N668US), experienced a loss of power from the No. 1 engine while in cruise flight over the Pacific Ocean northeast of Japan. The pilots reported the airplane was level at flight level 320 on the G344 airway between the CUTEE and CARTO waypoints when a sudden thump occurred and the airplane yawed to the left. After the thump, the No. 1 engine's engine pressure ratio (EPR) and N1 decreased, exhaust gas temperature (EGT) increased, and oil quantity indicated about 9 quarts. The airplane was stabilized with the rudder, and when the EGT limit was reached, the engine thrust lever was retarded to idle. The Engine Failure Checklist was accomplished, and the VNAV drift down procedure was initiated with a 45° turn off track to the right. The pilots declared an emergency, and the airplane descended to flight level 280. After consulting with Delta Air Lines' dispatch and maintenance in Atlanta, Georgia, the flight crew decided to divert back to Tokyo Narita International Airport (NRT). About 30 minutes before landing, fuel was jettisoned to reduce the airplane's weight below the maximum landing weight. The airplane landed at NRT without further incident. The flight was operating under 14 CFR Part 121 as a scheduled international flight from NRT to Detroit Metropolitan Wayne County International Airport.
Injuries
There were no injuries to the 4 pilots, 13 flight attendants, and 309 passengers on board.
Personnel Information
The captain, aged 61, held an Air Transport Pilot certificate with multiple ratings and a first-class medical certificate dated March 21, 2017, with no limitations. His most recent proficiency check was on December 14, 2016. He had 11,528 total flight hours, with 6,082 hours in the Boeing 747-400. The first officer, aged 59, also held an Air Transport Pilot certificate and a first-class medical certificate dated February 11, 2017. He had 19,591 total flight hours, with 507 hours in the Boeing 747-400.
Aircraft Information
The airplane was a Boeing 747-451, serial number 24223, registered as N668US, operated by Delta Air Lines. It was a four-engine transport category airplane with a maximum takeoff gross weight of 870,000 pounds. The airplane was manufactured in 1990 and originally delivered to Northwest Airlines; Delta acquired it through merger. At the time of the incident, the airplane had accumulated 113,100 flight hours. The No. 1 engine was a Pratt & Whitney PW4056, serial number P717513, a dual-spool, axial-flow, high-bypass turbofan engine. According to Delta's maintenance records, the engine had accumulated 82,303 hours and 10,645 cycles since new, and 5,446 hours and 600 cycles since its last overhaul in May 2014.
Flight Recorders
The airplane was equipped with a cockpit voice recorder (CVR) and a digital flight data recorder (DFDR). The DFDR was read out by the NTSB. The CVR was not removed because the elapsed time would have resulted in the event being overwritten. DFDR data showed that prior to the incident, all four engines' N2 rpm, EPR, EGT, and fuel flow were evenly matched. At the time of the event, the No. 1 engine's parameters changed significantly: EPR dropped from 1.29 to 0.76, N2 decreased, EGT increased, and fuel flow decreased. Later, the fuel cutoff parameter changed to Cutoff, and EGT reached a maximum of 751°C before decreasing.
Damage to Airplane
There was no damage to the airplane other than minor impact damage to the interior surfaces of the No. 1 engine's core cowls. The inboard core cowl had two small splits in the skin, but no debris appeared to have passed through.
Fire
There was no fire.
Tests and Research
The No. 1 engine was removed and sent to Delta's TechOps facility for disassembly. Examination revealed extensive damage through the high-pressure compressor (HPC), high-pressure turbine (HPT), and low-pressure turbine (LPT). The LPT case had a 360° split in line with the 6th stage turbine rotor. HPC blades from the 5th to 15th stages were damaged, with fatigue fractures found in many 6th through 9th stage blades. Two variable inlet guide vanes were missing, with overload fractures. The HPT and LPT also showed thermal and mechanical damage. The 5th stage compressor blade that fractured was part number 58H305, which had a history of airfoil fractures in the PW4000 94-inch fan engine family. However, no specific cause for the event was identified in the report.