History of Flight
On July 28, 2012, at 1600 eastern daylight time, a Boeing 787-8, registration VT-ANJ, experienced an engine failure during a taxi test at Charleston AFB / International Airport (CHS), Charleston, South Carolina. The airplane was being operated by Boeing under 14 CFR Part 91 for a taxi test with no intention for flight. There were no injuries among the 5 people on board, and the airplane sustained minor damage.
The crew taxied onto runway 21 for the first of two taxi tests. The test was planned as a low-speed run with a maximum speed of 60 knots.
At approximately 16:00:32, the flight crew commanded takeoff power of 95.4% N1 (low pressure rotor speed). As the airplane approached 40 knots and before the engine N1 accelerated beyond 70%, the right engine N1 began to roll back, and an EICAS advisory message displayed an N2 (high pressure rotor speed) exceedance.
At 16:00:40 and about 40 knots, the flight crew reduced engine power to idle and advised air traffic control they had completed their test. The crew exited the runway via a left turn onto taxiway hotel, and during taxi back to the ramp, shut down the right engine.
Subsequently, Southwest Airlines flight 2414 was cleared for takeoff on runway 21 and reported a fire developing in the grass on the right side of the runway. Due to the fire's proximity, air traffic control suspended runway 21 operations and notified Airlift Wing Operations (AMOPS) at about 1605.
After the fire department extinguished the fire, AMOPS conducted a runway inspection and discovered metal foreign object debris (FOD) on the first 4,000 feet of runway 21 prior to the intersection of taxiway foxtrot.
During post-taxi inspection on the ramp, Boeing crew identified damage to the airplane and notified air traffic control.
Injuries
There were no injuries to the 5 crewmembers on board.
Damage to Airplane
The airplane had numerous impact marks and small holes on the underside of the right wing, the right side of the fuselage aft of the wing, and the right side of the horizontal stabilizer. Examination of the right engine revealed extensive damage to the low pressure turbine (LPT).
The fan mid shaft (FMS) retaining nut was still connected to the FMS threads, but the forward part of the FMS, from the rear of the forward threads, was separated from the remainder. Separation of the rotating LPT section from the fan allowed the LPT section to translate rearward, resulting in extensive secondary engine damage.
Personnel Information
The flight crew consisted of two pilots and three additional crewmembers. The captain reported approximately 12,500 hours total time, including about 9,700 hours as pilot-in-command and 174 hours in the B787. He held a valid FAA Airline Transport Pilot certificate with type ratings for B737, B747-4, B757, B767, B777, and B787 and a current first-class medical certificate with no limitations.
The first officer reported approximately 6,700 hours total flight time, including about 4,200 hours as pilot-in-command and about 44 hours in the B787. He held a valid FAA ATP certificate with type ratings for DC-9, B737, and B787 and a current first-class medical certificate with a limitation requiring corrective lenses.
Aircraft Information
VT-ANJ, manufacturer serial number 36281, was a Boeing 787-8 equipped with two General Electric GEnx-1B67 engines. The airplane had approximately 0 hours total time on the airframe. Recorded data and company records indicated no relevant maintenance issues. At the time of the incident, the airplane was operating at an estimated weight of 351,441 pounds with 13,455 gallons of fuel on board.
The right engine, GE GEnx-1B, engine serial number (ESN) 956-121, had operated a total of 18:16 hours: 9:21 hours in a test cell, and 8:55 hours after installation on the airplane.
The fan mid shaft was a tubular shaft made of ultrahigh duplex strengthened steel. It transmitted rotational energy from the LPT to the fan and booster. The FMS was about 8 feet long, manufactured of GE1014 ultrahigh strength steel. It included threads on interior and exterior surfaces. The inside coupled to the center vent tube (CVT); the exterior joined the FMS with the forward fan shaft using a locking nut and washer. Threads were coated with a cured dry film lubricant, and petrolatum graphite grease was applied to aid assembly.
The FMS was originally forged by ATI-Allvac in Monroe, North Carolina in September 2006. In June 2007, it was shipped to IHI Corporation in Japan for manufacturing steps including rough turning, finish turning, splining, balancing, and final inspection in June 2008. It was shipped to General Electric in Kentucky in November 2008 and in October 2010 to GE in North Carolina, where it was installed in the LPT module. The LPT module was installed on the engine in November 2010.
Meteorological Information
At 1556 EDT, the CHS surface observation reported wind from 220 degrees at 12 knots gusting to 19 knots, visibility 10 miles, few clouds at 3,000 feet, scattered clouds at 4,200 feet, temperature 33°C, dew point 25°C, and altimeter setting 29.95 inches of mercury.
Aerodrome Information
Charleston AFB / International (CHS) was a civilian/military joint-use airport about 9 miles northwest of Charleston, South Carolina. Operations used four runways. Runway 21 was grooved concrete, 7,000 feet long, 150 feet wide with a touchdown zone elevation of 40 feet. It had precision markings and intersected runway 15/33 about 800 feet from the approach end.
Flight Recorders
Two Enhanced Airborne Flight Recorders (EAFR) were installed. The forward EAFR, serial number 16PLHY, was removed and sent to the NTSB Vehicle Recorder Division. The recording contained about 35.1 hours of data; the incident session was approximately 2 hours 6 minutes. The voice recorder had 2 hours 3 minutes 59 seconds of recording on four audio channels. The event was captured on the first segment from 15:35:48 to 16:55:56. Audio quality was good to excellent.
Wreckage and Impact Information
The front portion of the FMS with attached retaining nut and CVT were removed and sent to GE Cincinnati for metallurgical examination. The remainder of the engine was then removed and sent to GE Cincinnati for disassembly and examination.
Tests and Research
Engine Examination
Exterior examination of the engine showed no indication of uncontainments, case ruptures, or under-cowl fires. The fan disk was intact with all blades and platforms in place. The LPT case was intact but had numerous outward dents and a hole. From LPT stage 2 rearward, there was evidence of extensive damage such as fractured or missing blades, nozzles, or shroud segments.
There were no impact marks or holes inside the engine cowls; all airframe impact damage was downstream of the engine's tailpipe.
During bearing examination, the number 5 bearing inner retaining nut breakaway torque was 320 foot-pounds, compared to the GE assembly procedure requirement of 600–720 foot-pounds.
Fan Mid-Shaft Examination
Boroscope inspection confirmed separation of the FMS adjacent to the lock nut face at the aft-most full thread root. The fracture exhibited distinct color differences: about 85% had discoloration consistent with progressive fracture, and the remaining showed signs of instantaneous overstress failure.
SEM examination revealed faceted, quasi-cleavage fracture features consistent with environmentally assisted cracking (EAC) specific to ultrahigh strength steel GE1014.
The thread root region adjacent to the cracking had thin dry film lubrication thicknesses less than prescribed minimums, particularly on 45° thread flanks; some regions within the thread root appeared bare. The 7° thread flanks generally met minimum thickness but tapered below near the thread root.
Chemical and Mechanical Testing
Bulk hydrogen analysis showed hydrogen content below specification maximum. Chemical analysis found elements consistent with dry film lubricant, graphite grease, or synthetic engine oil used in assembly. No other foreign contaminants were observed.
Tests to determine absorption tendencies of two dry film lubricants showed that Everlube 9002 (used on the incident FMS) absorbed water 3.5 times greater than MolyDag 254.
Mechanical testing indicated the FMS met or exceeded requirements for ultimate tensile strength.
Test specimens of GE1014 were fabricated to replicate stress concentration at the aft-most thread root. Dynamic load cycling was applied; 18 tests at two laboratories showed no fractures after each specimen underwent 42,000 cycles over 250 days.
Environmental Testing
A series of 168 static two-point bend tests of FMS material were conducted in a humid bed. Various combinations of dry film lubricant, grease, and synthetic oil were tested. Two GE1014 specimens fractured: one at 43 days with Everlube 9002 and graphite grease, and the second at 149 days with Everlube 9002 and synthetic engine oil. Both failed at lower static stress and higher humidity.
Corrosion testing revealed that bare GE1014 steel exhibited a lower corrosion rate than GE1014 coated with Everlube 9002.
Organizational and Management Information
The Boeing Company corporate headquarters was in Chicago, Illinois, employing about 169,000 people worldwide. Boeing South Carolina fabricated, assembled, and installed aft fuselage sections on the 787 Dreamliner and included the final assembly and delivery facility at CHS.
Additional Information
Following the FMS separation on ESN 956-121, GE developed an ultrasonic inspection to scan the forward end of the FMS in the thread area. During inspections on all GEnx engines in service and storage, a GEnx-1B engine, ESN 956-175, installed on a B787-8, was found to have an indication of a similar crack. This airplane had not yet been operated in flight; the engine had only been operated during post-production tests and ground runs.
Follow-up testing indicated the crack on ESN 956-175 was similar to that on ESN 956-121: consistent with progressive environmentally assisted cracking emanating from the thread root region.
After discovery of the second cracked FMS, the National Transportation Safety Board issued two urgent recommendations to the Federal Aviation Administration: (1) Issue an airworthiness directive to require, before further flight, ultrasonic inspection of the fan mid shaft in all GE GEnx-1B and -2B engines that had not yet undergone inspection (A-12-52). (2) Require operators to accomplish repetitive inspections of the FMS in all (on-wing and spare) GE GEnx-1B and -2B engines at a sufficiently short interval to permit multiple inspections and detection of a crack before critical length (A-12-53).
In response, the FAA issued Airworthiness Directive AD-2012-19-08, requiring initial and repetitive ultrasonic inspection of GE GEnx-1B and -2B engine fan mid shafts for cracks.
GE ceased use of Everlube 9002 and graphite grease for GEnx engine assemblies. All engines assembled with the original dry film lubricant and graphite grease combination have been inspected multiple times and are required by Airworthiness Directive to be inspected within every 100 hours of operation.