What happened
On March 13, 2025, at approximately 1759 mountain daylight time, an American Airlines Boeing 737-823, registration N885NN, experienced engine vibrations during takeoff from Colorado Springs Airport (COS). The flight crew continued the takeoff but subsequently diverted to Denver International Airport (DEN).
During the takeoff roll, just before reaching V1, the crew noted an Exhaust Gas Temperature (EGT) over-temperature on the No. 2 (right) engine. After the landing gear and flaps were retracted, the crew reduced power on the right engine, which brought the EGT back within limits. However, during the climb, the captain identified high engine vibration on the right engine and initiated the High Engine Vibration checklist. After consulting with dispatch, the crew decided to divert to Denver.
The aircraft landed at DEN under visual meteorological conditions. While taxiing to the gate, airport operations video captured fluid leaking from beneath the right engine nacelle. After the engines were shut down at the gate, a fire began in the area of the No. 2 engine. The fire spread to the cabin, with smoke filling the aircraft, prompting the flight attendants to initiate an evacuation. Gate ramp personnel extinguished the fire within one minute, before the arrival of Denver airport fire fighting and rescue (ARFF) units.
Of the 172 passengers and 6 crew members on board, 12 passengers sustained minor injuries. The aircraft suffered substantial damage.
The investigation
The aircraft was moved to a maintenance hangar for inspection. Investigators found evidence of heat, smoke, and burns on the right engine nacelle, the right wing, the right side of the aft fuselage, the right main landing gear, and the right main landing gear wheel well.
An examination of the right engine revealed that while the nacelle remained intact, it showed soot and thermal distress consistent with a ground fire. Mechanical findings included:
- A fractured platform on one engine fan blade.
- Loose and incorrectly installed lockwire on a fuel fitting of the variable stator vane (VSV).
- An incorrectly fastened VSV actuator rod end, which allowed fuel to leak from the fitting.
- A fracture in the weld of the VSST rod end muscle line.
- A blockage in the 6 o’clock seal drain line of the inboard thrust reverser half caused by sealant.
Regarding the evacuation, the L2 door was found with the escape slide jammed in the door, preventing its use. The L2 slide had been removed from its bustle and was found on the floor of the passageway.
The investigation also involved the review of the cockpit voice recorder (CVR) and flight data recorder (FDR). The FDR provided approximately 54 hours of data, including the flight in question. Maintenance records for the right engine were also reviewed.