Delta B744 over Pacific on Jun 7th 2017, engine shut down in flight

Last Update: August 11, 2020 / 21:20:35 GMT/Zulu time

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Incident Facts

Date of incident
Jun 7, 2017

Classification
Incident

Flight number
DL-276

Aircraft Registration
N668US

Aircraft Type
Boeing 747-400

ICAO Type Designator
B744

A Delta Airlines Boeing 747-400, registration N668US performing flight DL-276 from Tokyo Narita (Japan) to Detroit,MI (USA) with 309 passengers and 18 crew, was enroute at FL320 over the Pacific Ocean about 1570nm northeast of Tokyo when the crew reported problems with the #1 engine (PW4056, outboard left hand), descended the aircraft to FL280 and decided to return to Tokyo Narita, where the aircraft landed back about 7 hours after departure.

A passenger reported about 3.5 hours into the flight there was noise and vibrations. Soon after the aircraft descended to FL280 and turned around. The captain announced that one of the engines had ceased operation, Tokyo Narita was still the closest airport and they would return to Narita. The passengers were put into hotels and rebooked onto flight DL-9876 the following day, however, that flight was cancelled. A number of passengers have been rebooked onto DL-276 of Jun 8th.

Japan's Ministry of Transport reported the aircraft declared emergency due to engine trouble.

On Jun 16th 2017 the NTSB reported, that the #1 engine lost power associated with a thump sound and yawing of the aircraft, the EGT went above the red line and the engine automatically shut down. The crew deviated from the Pacific Track, declared emergency and descended the aircraft to FL280, then returned to Tokyo Narita. Post landing examination revealed metallic debris in the tail pipe of the engine and a 360 degrees crack in the low pressure turbine case just forward or the rear flange.

On Aug 11th 2020 the NTSB released their factual report summarizing, the aircraft

experienced a loss of power from the No. 1 engine, a Pratt & Whitney (P&W) PW4056, while in cruise flight over the Pacific Ocean northeast of Japan. The pilots reported that the airplane was level at FL 320 on the G344 airway between the CUTEE and CARTO waypoints when there was a sudden thump and the airplane yawed to the left. The pilots further reported that following the thump; the No. 1 engine's EPR [engine pressure ratio] and N1 were decreasing, the EGT [exhaust gas temperature] was increasing, and the oil quantity indicated about 9 quarts. The airplane was stabilized with the rudder and as the engine's EGT limit was reached, the engine's thrust lever was retarded to idle. The Engine Failure Checklist was accomplished and the VNAV drift down procedure was initiated while turning 45° off track to the right. The pilots declared an emergency and the airplane descended to FL 280. After consulting with Delta Air Lines' dispatch and maintenance at Atlanta, Georgia, it was determined that the airplane would divert back to Tokyo Narita International Airport (NRT), Tokyo, Japan. The pilots reported that about 30 minutes prior to landing, they jettisoned fuel to reduce the airplane's weight to below the maximum landing weight. The airplane landed at NRT without further incident.

The NTSB described tests and research with the #1 engine:

The initial examination of the HPC revealed that all of the HPC airfoils, from the 5th to the 15th stage, were damaged with nicks, dents, and tears to the leading and trailing edges and/or were broken off at various lengths above the blade root platforms. There was one 5th stage compressor blade that was fractured transversely across the airfoil adjacent to the blade root platform and had an elliptical-shaped pattern on the fracture surface that radiated from the convex side of the airfoil. There were many 6th, 7th, 8th, and 9th stage compressor blades that were fractured transversely across the airfoils adjacent to the blade root platforms and many of those blades had elliptical-shaped patterns on the fracture surfaces that radiated mostly from the convex side of the airfoil. The disassembly of the HPC also revealed two variable inlet guide vanes (IGV) that were missing and the airfoils were fractured adjacent to the outer button. The 5th through 9th stage compressor blades and the two variable IGVs were removed from the engine and sent to P&W's Material and Processes Engineering Laboratory for metallurgical examination. The 5th stage compressor with the elliptical-shaped pattern on the fracture surface was lost during the shipment between Delta and P&W. The examination of the remaining 5th stage compressor blades revealed fracture surfaces that were consistent with overload or were too smeared and damaged to be able make an assessment of the fracture surface. However, the examination of the 6th through 9th stage compressor blades with the elliptical-shaped pattern showed that those patterns were fatigue fractures. The examination of the two variable IGVs revealed fracture surfaces that were consistent with overload. Because of the large number of HPC blades with fatigue cracks, the Powerplants Group made a more extensive examination of the LPC and HPC to look for something that may have caused the fatigue cracking but nothing was found.

The HPT and LPT also had extensive damage. The HPT, both stage 1 and 2, had the tips of all of the airfoils missing. The stage 1 blade tips appeared to have been burned off and the stage 2 blade tips appeared to have been broken off. The 3rd stage turbine vanes, the first stage in the LPT, had an arc between about 5 and 7 o'clock, where the airfoils were burned out and the remaining airfoils were thermally damaged. The 4th stage turbine vanes had an arc between about 4 and 8 o'clock where the airfoils were missing and appeared to have been broken out. All of the LPT blades, stages 4 through 6, were in place, but all were damaged with nicks, dents, and being broken at various lengths above the blade root platform. There were some 6th stage turbine blade that were almost full length.

The examination of the engine revealed the LPT case had a 360° split in line with the 6th stage turbine rotor. The LPT case did not have areas were the edges of the split were pursed radially outward nor was the case bulged outward. In addition to the LPT case being split, the 6th stage blade outer airseal segments (BOAS) were broken up circumferentially as well as axially. The edges of the split in the LPT case matched the edges of the circumferential breaks in the 6th stage BOAS that matched the shape of the 6th stage turbine blade tip shroud.

The NTSB described the history of the 5th stage HPC blades:

The PW4000 94-inch fan engine has had a long history of 5th stage compressor blade fractures. The fractured 5th stage compressor blade was part number (PN) 58H305. According to P&W, the PN 58H305 blade has had 16 airfoil fractures. The PN 58H305 blade superseded another part numbered blade that had 22 airfoil fractures. The PN 58H305 was itself superseded by the PN 50S805 blade in 2011 that according to P&W has not yet had a reported blade fracture.

The PN 58H305 blade as well as the superseded blade has also had a number of blade root fractures. Although the PW4000 94-inch engine has had a number of 5th stage compressor blade fractures in the airfoil and root, only one was reportable to the NTSB in accordance with 49 CFR 830.5 and subsequently investigated. That incident involved a Delta Air Lines Boeing 747-451 airplane that had a 5th compressor blade, which was a PN 58H305 blade, fracture through the root shank during take off from Atlanta. (Reference: ENG14IA027) (Editorial note: see also Incident: Delta B744 at Atlanta on Sep 21st 2014, engine shut down in flight). The resultant vibration following the blade fracture loosened the B-nut on a hydraulic line causing a leak and leaking the hydraulic fluid ignited off of the hot engine cases. The blade fractured from a fatigue crack that was caused by the improper grit blasting of the blade's root shank during the overhaul of the blade by a repair vendor.
Incident Facts

Date of incident
Jun 7, 2017

Classification
Incident

Flight number
DL-276

Aircraft Registration
N668US

Aircraft Type
Boeing 747-400

ICAO Type Designator
B744

This article is published under license from Avherald.com. © of text by Avherald.com.
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