Wednesday, October 04, 2017

Boeing 757-200, N686DA: Incidents occurred December 29, 2020 and September 06, 2017

Federal Aviation Administration / Flight Standards District Office; New York, New York

Aircraft  #1 engine was on fire after landing. 

Delta Air Lines Inc

Date: 29-DEC-20
Time: 01:12:00Z
Regis#: N686DA
Aircraft Make: BOEING
Aircraft Model: 757-200
Event Type: INCIDENT
Highest Injury: NONE
Aircraft Missing: No
Damage: UNKNOWN
Activity: COMMERCIAL
Flight Phase: TAXI (TXI)
Operation: 121
Aircraft Operator: DELTA
Flight Number: DAL1886
City: NEW YORK
State: NEW YORK

 




















Aviation Accident Final Report - National Transportation Safety Board

The National Transportation Safety Board did not travel to the scene of this incident.

Additional Participating Entities:
Delta Air Lines; Atlanta, Georgia 
Pratt & Whitney; East Hartford, Connecticut
Boeing; Long Beach, California 
Federal Aviation Administration; Burlington, Massachusetts
Air Line Pilots Association International; Atlanta, Georgia 

Investigation Docket - National Transportation Safety Board:

Location: Las Vegas, Nevada
Incident Number: ENG17IA036
Date & Time: September 6, 2017, 00:19 Local
Registration: N686DA
Aircraft: Boeing 757 232 
Aircraft Damage: None
Defining Event: Powerplant sys/comp malf/fail
Injuries: 184 None
Flight Conducted Under: Part 121: Air carrier - Scheduled

Analysis

The No. 1 engine fire was caused by an improperly installed #7 fuel nozzle located at the 3 o'clock position of the engine. The nozzle installation error resulted in a fuel leak that subsequently ignited on hot engine case surfaces. All the fuel nozzles had been replaced as part of engine overhaul at the Delta Tech Ops facility 53.7 flight hours/18 cycles prior to the incident flight.

The cross threaded condition was evident during visual examination, and an x-ray of the fuel nozzle assembly confirmed the fuel nozzle b-nut was not properly seated, with one or fewer threads engaged. The nozzle assembly featured two o-rings and a conical seal washer (Voi-Shan) that acted in conjunction with the torque applied to the fuel nozzle b-nut to provide a seal. The o-rings and seal washer temporarily compensated for the cross threaded condition, until one of the o-rings began to break apart.

The cross threaded b-nut should have been visually detected by the mechanic and inspector. Although, if not visually detected, the cross threaded b-nut may have given a proper torque indication during the required torque check and passed the pneumatic leak check step of the installation procedures.

Several fuel system components including the fuel flow transmitter and stator vane actuator are located near the #7 fuel nozzle. The fire thermally damaged the case housings of both of these components resulting in secondary fuel leaks. The damage to the nacelle components including the fan cowl, thrust reverser, and core cowls was due to fire exposure. The area of thermal insulation on the right thrust reverser half that was minimally discolored with a wet and shiny appearance was located radially outboard of the #7 fuel nozzle. The fuel spray from the nozzle provided localized cooling where the fuel contacted the insulation and was too rich to ignite, preserving the fire insulation.

The fan blade shroud shingling and displacement noted on three fan blades was most likely a result of firefighting efforts. After the blades were dislodged from the rub strip, the fan spun smoothly.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this incident to be:
A No. 1 (left) engine undercowl fire caused by a fuel nozzle installation error during engine overhaul at Delta TechOps. A fuel nozzle b-nut was cross threaded, which allowed fuel to leak on hot engine case surfaces and subsequently ignite.

Findings

Aircraft Fuel injector nozzle - Incorrect service/maintenance

Factual Information

HISTORY OF FLIGHT

On September 6, 2017, at about 0019 PDT, a Delta Air Lines Boeing 757-232, registration N686DA, equipped with two Pratt & Whitney PW2037 turbofan engines, experienced a No. 1 (left) engine undercowl fire during takeoff from McCarran International Airport (LAS), Las Vegas, Nevada. The flight crew reported a left engine fire indication and associated aural fire alert at rotation/initial climb.  The crew completed the quick reference handbook (QRH) procedures, declared an emergency, shut down the left engine and discharged one of the fire bottles; the fire warning momentarily was cleared. They then initiated engine out procedures to return to LAS airport. During the downwind leg of the airplane's flight pattern, the fire warning indication re-illuminated, and the second fire bottle was discharged, which cleared the fire warning a second time. The airplane made an uneventful overweight landing at LAS and was met by aircraft rescue and firefighting (ARFF) on the runway. ARFF sprayed fire retardant into the engine and confirmed the fire was extinguished. The airplane was cleared to taxi to the gate under its own power. There were no passengers or crew injuries reported. The flight was being operated in accordance with 14 Code of Federal Regulations Part 121 and was a regularly scheduled flight from LAS to John F. Kennedy International Airport (JFK), Queens, New York.

DAMAGE TO THE AIRPLANE

There was no damage to the airplane structure. The left engine thrust reverser exhibited thermal damage and discoloration on all interior surfaces except for a localized area between the 1 and 3 o'clock positions where the insulation appeared wet and shiny. The core cowls were thermally damaged, deformed and missing material.

TEST AND RESEARCH

Engine Examination and Disassembly

The No. 1 engine was removed from the airplane by Delta Air Lines (DAL) maintenance personnel at LAS and shipped to Delta TechOps- Atlanta, Georgia for examination and disassembly. Party members from DAL, Pratt & Whitney (P&W), Boeing, the Air Line Pilots Association (ALPA), the Federal Aviation Administration, and the National Transportation Safety Board met at Delta TechOps from September 26-28, 2017.

The compressor fan blades were all present and complete. Three fan blades located at the 6 o'clock position exhibited midspan shroud shingling and the fan blade tips were dug into the fan case rub strip and displaced about one inch in the aft direction. The fan could not be rotated by hand until the three shingled fan blades were forced back into their normal position with a pry bar. After the fan blades were adjusted, the fan could be spun smoothly by hand with concurrent rotation of the low pressure turbine. All exterior engine surfaces aft of the fan exit case were sooted. The engine had thermal damage and dark discoloration most concentrated over the high pressure compressor (HPC) and diffuser cases on the lower half of the engine (3 to 9 o'clock positions). Fuel components including the stator vane actuator (SVA), fuel flow transmitter (FFT), and associated fuel lines were thermally damaged with melted and missing material. The thermal damage to these components resulted in fuel system leak points. A SVA hose and tube assembly was found separated and hanging freely from the engine. A leak check of the fuel manifolds and fuel nozzle assemblies was performed by porting shop air into the fuel flow divider valve in accordance with engine maintenance manual procedures. When pressurized air was applied, an air leak was detected at fuel nozzle #7, located at the 3 o'clock position. The nozzle was removed from the engine as an assembly by cutting the fuel manifold supply line, so the fuel nozzle b-nut remained torqued. Preliminary x-rays of the nozzle were taken at Delta TechOps. The x-rays indicated the fuel nozzle b-nut was not properly installed. The fuel nozzle assembly SVA hose and tube assembly that was found separated were packaged and shipped to the P&W Materials and Processes Engineering Lab in East Hartford, Connecticut for additional analysis.

Materials Analysis

Fuel nozzle #7 was x-rayed at the P&W Quality and Standard Laboratory in East Hartford, Connecticut. The x-ray images confirmed that the b-nut was tilted relative to the nozzle platform and the end of the bnut was not centered with the nozzle fuel supply tube (cross threaded). There was one or fewer threads engaged between the nozzle and b-nut.

The fuel nozzle assembly was sectioned. The o-ring on the fuel nozzle side was present and intact. The second o-ring located on the fuel manifold supply line side was damaged and o-ring fragments were recovered outside of the o-ring gland, near the conical washer seal. 

The SVA hose and tube assembly was examined to verify there were no anomalies in the SVA flexible hose to rigid tube connection joint. The SVA flexible hose section exhibited thermal damage including a missing fire sleeve and hose liner. The hose liner was separated at one end of the connection to the rigid tube, but other joint connection remained intact. Metallographic sections were taken of both the intact joint and the separated joint and there were no significant differences observed.

ADDITIONAL INFORMATION

Corrective Action

Following the event, DAL voluntarily inspected all PW2000 engines in the Delta TechOps repair shop, test cell, and spares pool for proper fuel nozzle installation, with no additional installation error findings. They also reviewed shop records and identified two in service engines that were overhauled/repaired at approximately the same time as the incident engine. The fuel nozzles on these engines were inspected with no findings. In an effort to avoid future installation errors, the diffuser and combustor assembly work instruction card was updated to add an inspector sign off requirement during the pneumatic leak check step of the fuel system assembly.

History of Flight

Takeoff Fire/smoke (non-impact)
Initial climb Powerplant sys/comp malf/fail (Defining event)

Pilot Information

Certificate: Age:
Airplane Rating(s): 
Seat Occupied:
Other Aircraft Rating(s):
Restraint Used:
Instrument Rating(s):
Second Pilot Present:
Instructor Rating(s):
Toxicology Performed:
Medical Certification:
Last FAA Medical Exam:
Occupational Pilot: 
Last Flight Review or Equivalent:
Flight Time:

Aircraft and Owner/Operator Information

Aircraft Make: Boeing
Registration: N686DA
Model/Series: 757 232 232 
Aircraft Category: Airplane
Year of Manufacture: 1995
Amateur Built: No
Airworthiness Certificate: 
Transport Serial Number: 27589
Landing Gear Type: Retractable - Tricycle
Seats:
Date/Type of Last Inspection: Certified
Max Gross Wt.: 248020 lbs
Time Since Last Inspection: 
Engines: 2 Turbo fan
Airframe Total Time: 
Engine Manufacturer: Pratt & Whitney
ELT: Installed, not activated 
Engine Model/Series: PW2037
Registered Owner: 
Rated Power: 34640 Lbs thrust
Operator: 
Operating Certificate(s) Held: Flag carrier (121)

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual (VMC)
Condition of Light: Night
Observation Facility, Elevation: KLAS,2180 ft msl
Distance from Accident Site: 1 Nautical Miles
Observation Time: 00:19 Local 
Direction from Accident Site: 213°
Lowest Cloud Condition: 
Visibility:
Lowest Ceiling: 
Visibility (RVR):
Wind Speed/Gusts: / 
Turbulence Type Forecast/Actual:  /
Wind Direction:
Turbulence Severity Forecast/Actual: /
Altimeter Setting:
Temperature/Dew Point:
Precipitation and Obscuration:
Departure Point: Las Vegas, NV (LAS)
Type of Flight Plan Filed:
Destination: New York, NY (JFK) 
Type of Clearance: Unknown
Departure Time: 00:19 Local 
Type of Airspace: Unknown

Airport Information

Airport: McCarran Intl LAS
Runway Surface Type:
Airport Elevation: 2181 ft msl 
Runway Surface Condition: Unknown
Runway Used: 
IFR Approach: Unknown
Runway Length/Width:
VFR Approach/Landing: Unknown

Wreckage and Impact Information

Crew Injuries: 6 None
Aircraft Damage: None
Passenger Injuries: 178 None
Aircraft Fire: In-flight
Ground Injuries: N/A 
Aircraft Explosion: None
Total Injuries: 184 None 
Latitude, Longitude: 36.083889,-115.15361(est)

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