Skywest CRJ7 at Denver on Jul 2nd 2017, engine fire on landing

Last Update: August 3, 2022 / 16:55:17 GMT/Zulu time

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Incident Facts

Date of incident
Jul 2, 2017

Classification
Accident

Flight number
OO-5869

Aircraft Registration
N796SK

Aircraft Type
Canadair CRJ-700

ICAO Type Designator
CRJ7

A Skywest Airlines Canadair CRJ-700 on behalf of United, registration N796SK performing flight OO-5869 from Aspen,CO to Denver,CO (USA) with 59 passengers and 4 crew, landed on Denver's runway 34R and was vacating the runway when flames became visible from the ground and the left hand engine (CF34). The aircraft stopped on taxiway F near the northern end of F, the passengers rapidly deplaned the aircraft via aircraft stairs. Emergency services sprayed the left hand engine and ground and quickly extinguished the fire. There were no injuries, the aircraft sustained substantial damage as result of the fire.

A runway inspection found no debris on the runway.

The runway remained closed for about 50 minutes until the NTSB gave their clear to return the runway to service.

The FAA reported a tyre fire spread to the engine, the fire was extinguished. There were no injuries, the damage is being assessed.

On May 18th 2019 the NTSB released their preliminary report stating: "On July 02, 2017, about 1319 central daylight time, SkyWest Airlines flight 5869, a Bombardier CL 600-2C10, N796SK, experienced a left engine undercowl fire while landing at Denver International Airport (KDEN), Denver, CO. The flight crew reported that they received a L ENG SRG OPEN caution followed by a L ENG FIRE warning after stowing the thrust reversers. Both fire extinguishing bottles were discharged but the fire continued. Fire was observed at the left engine inlet, left engine aft pylon, and on the ground below the left nacelle and an emergency evacuation was initiated on the taxiway. The fire was extinguished by airport rescue and firefighting. There were no injuries to the 59 passengers and crew members onboard. The airplane was substantially damaged by the fire."

On May 27th 2022 the NTSB released their final report (docket) concluding the probable causes of the accident were:

The fuel supply tube fitting pulling out of the left engine’s operability bleed valve (OBV) during the landing rollout, allowing fuel to leak and contact hot engine cases, which ignited a fire that caused thermal damage to the engine pylon. Contributing to the fitting pullout from the OBV was an undetected progressive environmental control system (ECS) support link wear condition that allowed excessive OBV movement relative to the engine, and the lack of alignment instructions in the base engine assembly drawing and the lack of maintenance tasks to assess the operational condition of the ECS links.

The NTSB analysed:

After the scheduled air carrier flight touched down on the runway, a left engine undercowl fire occurred. The fire occurred after leaked fuel accumulating inside the engine core compartment (a fire zone) ignited from contact with a hot engine surface. The fuel accumulated inside the core compartment because the nacelle drainage system was overwhelmed by the release of about 34 gallons of fuel during the landing roll, at which time the high rates of ventilation through the nacelle were reduced.

The leak occurred during landing when the removal of fuel leakage depends in part on gravity drainage. A nacelle drainage capability assessment found that the core compartment contained about 20 gallons of fuel at the time of ignition. After engine shutdown, fuel draining from the core compartment was no longer carried overboard by the fan exhaust, and the fuel pooled in the fan duct. Some of this fuel drained to the ground through the transcowl drain holes. The fire became uncontrolled when it escaped the fire zone and spread to areas where expelled/drained fuel had accumulated in the nacelle and on the ground. The draining fuel led to a fire on the ground and on the underside of the left pylon. The fire was extinguished by airport rescue and firefighting personnel.

On-site investigation found that a rosan -05 to -06 expander fitting had pulled out from the fuel supply port of the operability bleed valve (OBV), which is part of the left engine’s environmental control system (ECS). Also, two ECS support links (which attach and support the ECS hardware, including the OBV, to the engine) were found severely worn.

Metallurgical examination of the OBV upper housing fuel supply port found evidence of advanced thread wear and fatigue damage, consistent with side-to-side fitting cyclic movement and insufficient remaining threads to prevent the fitting in the upper housing from pulling out.

Modal testing demonstrated that ECS link wear can shift the OBV natural operating frequency into the engine operating frequency range, significantly increasing the fuel tube loads into the fitting. OBV design evaluation testing found that fitting joint preload loss permits relative motion to occur between the fitting and upper housing port threads, initiating upper housing thread wear and leading to upper housing thread failure and fitting pullout. The rosan -05 to -06 expander fitting with the cast aluminum housing lacked the design margin to maintain sufficient preload against engine vibration loads and fitting pullout.

A review of CF34-8 maintenance engineering sheets and field maintenance documents found that rod end alignment instructions critical to preventing ECS support link wear were not provided in the base engine assembly drawing and that the ECS support links were not part of any scheduled airplane- or engine-level maintenance. As a result, maintenance personnel did not inspect for wear caused by poor rod end alignment. Worn or misaligned ECS support links increase fuel tube fitting loads and can result in fitting pullouts.
Aircraft Registration Data
Registration mark
N796SK
Country of Registration
United States
Date of Registration
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Manufacturer
BOMBARDIER INC
Aircraft Model / Type
CL-600-2C10
Number of Seats
ICAO Aircraft Type
CRJ7
Year of Manufacture
Serial Number
Aircraft Address / Mode S Code (HEX)
Engine Count
Engine Manufacturer
Engine Model
Engine Type
Pounds of Thrust
Main Owner
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Incident Facts

Date of incident
Jul 2, 2017

Classification
Accident

Flight number
OO-5869

Aircraft Registration
N796SK

Aircraft Type
Canadair CRJ-700

ICAO Type Designator
CRJ7

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