NTSB Factual Report

HISTORY OF FLIGHT

On March 19, 2017, about 1100 eastern daylight time (EDT), a McDonnell Douglas MD-83, N881GA, operated by Allegiant Air experienced a No. 2 (right) engine fire during approach to Dayton International Airport (DAY), Dayton, Ohio. The crew followed the quick reference handbook procedures, discharged both fire bottles, and shutdown the No. 2 engine. The airplane made an uneventful single engine landing at DAY and was met by aircraft rescue and firefighting (ARFF) vehicles on the runway. ARFF crews determined the fire had been extinguished and the airplane was cleared to taxi to the gate under its own power. The flight was a regularly scheduled flight from Orlando Sanford International Airport (SFB), Sanford, Florida to DAY and was conducted under the provisions of 14 Code of Federal Regulations Part 121. There were no reported passenger or crew injuries.

DAMAGE TO THE AIRPLANE

Allegiant Air maintenance crews performed a visual inspection of the No. 2 engine at DAY and reported significant thermal damage on the bottom half of the engine, concentrated around the constant speed drive (CSD) and generator. A section of the generator case was fractured and missing. The CSD-to-oil cooler return line located adjacent to the generator was severed. Oil pooling and metal debris were observed at the 6 o' clock position in the engine cowling.

TEST AND RESEARCH

Constant Speed Drive and Generator Examination and Disassembly

The digital flight data recorder (DFDR) engine parameters and photographs of the engine provided by maintenance personnel on scene at DAY were reviewed and it was determined that the failure was isolated to the No. 2 engine CSD or generator. Both components were removed from the engine and shipped to United Technologies Aerospace Systems in Rockford, Illinois for examination and disassembly.

The CSD was disassembled and fine metal debris was observed throughout the case, on all internal components and on the magnetic oil plug. The CSD gears and bearings were intact and the gear train could be manually rotated with some resistance.

The center section of the generator frame case was fragmented and missing. All generator rotating components exhibited severe thermal damage and deformation. The generator main rotor copper holding wedges, V-shaped steel wedges, and copper windings were separated. Several small copper holding wedge fragments were recovered from the generator case, but the parts were too damaged to perform materials analysis.

ADDITIONAL INFORMATION

A record of uncontained generator failures on Douglas Aircraft DC-9/ McDonnell Douglas MD-80 series airplanes was requested from UTC Aerospace Systems and Boeing. Eleven prior uncontained generator failure events were reported since the year 2000. The event descriptions for each of the prior 11 events were based on crew statements, and from the statements an accurate count of generator failures that resulted in an engine fire was inconclusive. It was confirmed that none of the events to date have resulted in an uncontrolled fire.

Following the events in 2010, Boeing provided the NTSB with a safety risk assessment. According to the assessment, any fragments released by an uncontained generator failure are low energy projectiles and do not pose a threat to the airframe. The assessment also states that design features including overboard drains, fire detection and extinguishing systems are in place to mitigate the risks associated with flammable fluid leaks in a designated fire zone.

In June 2005 Hamilton Sundstrand Corporation (now UTC Aerospace Systems) released service information letter (SIL) 449 recommending that air cooled generator rotors installed on Boeing 707, 727, 737, DC9, MD80, and DC10 airplanes should be overhauled and re-wound at 40,000 operating hours. As part of the overhaul, the interpole copper wedges are replaced. Boeing released a service letter, DC9-SL-24-104/MD-80-SL-24-104 in November 2005 notifying all operators of the SIL.

NTSB Probable Cause

The probable cause of the No. 2 (right) engine fire was an uncontained generator failure. Deformed rotating generator components and/or metal fragments radially released by the generator severed the constant speed drive-to-oil cooler return line located adjacent to the generator and caused oil to spray onto hot generator and engine case surfaces that subsequently ignited.