Douglas DC 9 83 N881GA incident near Dayton, Ohio

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.

NTSB analysis

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

The sections of the generator main rotor that remained intact and the metal fragments recovered from the generator case exhibited extensive thermal and impact damage that precluded material analysis.

The operating history of the failed generator was not available and federal regulations do not require operators to maintain hour and cycle counts for non-life limited components. An estimate of generator operating hours was provided by Allegiant Air and the date of manufacture was provided by UTC Aerospace Systems. Based on the available records the generator main rotor was never overhauled or re-wound and the total operating hours likely exceeded the 40,000 hour recommended overhaul interval specified in UTC Aerospace Systems service information letter (SIL) 449.

Text from the NTSB. Open the NTSB docket for ENG17IA017 for the full record.