US National Transportation Safety Board (NTSB) officials say both engines of a Frontier Airlines Airbus A319 (N924FR) that hit a half-dozen or more large birds on departure from Kansas City International airport on 14 November were damaged in the encounter.
Information from the crew and flight data recorders indicate that as the aircraft was climbing through 4,260ft enroute to Denver with 130 passengers and crew onboard, it struck "six or seven geese". The aircraft's right engine spooled down to flight idle after the collision, with attempts to advance the throttle again accompanied by "severe" compressor stalls that passengers described "fireballs being ejected from the engine", according to the NTSB's preliminary report of the incident.
After declaring an emergency, the pilots returned the aircraft to Kansas City and performed an uneventful landing using the left engine.
Officials say a post-landing inspection revealed damage to both engine inlet cowlings, though only internal damage to the right side CFM56 turbofan engine.
The US Airways A320 that successfully ditched in the Hudson River in January had received internal damage to both CFM56 engines during the encounter, which left the aircraft largely without thrust.