A20N, Atlantic City NJ USA, 2021
A20N, Atlantic City NJ USA, 2021
Summary
On 2 October 2021, an Airbus A320neo ingested a large bird into its right engine (a Pratt & Whitney PW1100G) during takeoff at Atlantic City and a high speed rejected takeoff followed. When leaked fuel pooling within the engine cowling subsequently ignited, an on-runway emergency evacuation was completed with the fire service in attendance. The Investigation identified the ingested bird as a bald eagle with a mass above the applicable certification standard and the fuel leak a secondary consequence of a fan blade broken by bird impact. Engine component design improvements to address the fire risk following large bird ingestion are being developed.
Event Details
When
02/10/2021
Day/Night
Day
Flight Conditions
On Ground - Normal Visibility
Flight Details
Aircraft
Operator
Type of Flight
Public Transport (Passenger)
Flight Origin
Intended Destination
Take-off Commenced
Yes
Flight Airborne
No
Flight Completed
No
Phase of Flight
Take Off
Location - Airport
Airport
BS
Tag(s)
Large Birds,
Engine damage,
Coastal or Large Inland Water Location,
Engine Ingestion
FIRE
Tag(s)
Fire-Power Plant origin
EPR
Tag(s)
Emergency Evacuation,
Evacuation Injuries
Outcome
Damage or injury
Yes
Aircraft damage
Minor
Non-aircraft damage
No
Non-occupant Casualties
No
Occupant Injuries
Few occupants
Off Airport Landing
No
Ditching
No
Safety Recommendation(s)
Group(s)
None Made
Investigation Type
Type
Independent
Description
On 2 October 2021, an Airbus A320 (N922NK) being operated by Spirit Airlines on a scheduled domestic passenger flight from Atlantic City to Fort Lauderdale as NK3044 ingested a large bird into its right engine during a daylight takeoff in normal ground visibility and the takeoff was rejected from just below V1 and the engine shut down. When a fuel-fed fire then fire ignited, an emergency evacuation was completed on the runway with four of the 109 occupants sustaining minor injuries during it including one identified as a crew member.
Investigation
An Engineering Investigation was carried out by the NTSB supported by downloaded SSFDR data and specialist input in respect of the bird species involved from the Smithsonian Institute. No assessment of the evacuation was carried out.
What Happened
Approximately 20 seconds after beginning takeoff roll a large bird was ingested into the right engine and with immediate indications of engine distress, the takeoff was rejected from just below the applicable V1 of 125 KIAS. About 40 seconds after the aircraft came to a stop, a fuel fed fire ignited within the engine cowling and was extinguished by the airport RFFS whilst an emergency evacuation was ordered and completed.
A subsequent initial examination of the aircraft and its geared turbofan engine by the Investigation team found no visible impact damage to the wing or any other part of the aircraft caused by ejected engine debris and the only significant airframe damage was to the right engine outboard thrust reverser translating sleeve which showed signs of thermal distress in the form of “blistered and consumed paint and slight damage to the sleeve skin panel (with) no burn-through holes observed”.
A more detailed on site examination of the engine found that one fan blade had been fractured near its root which essentially constituted a complete fan blade airfoil release. The root portion of the fractured fan blade remained in situ and “the fracture surface had a shiny and clean appearance”. There were no “breaches, tears, or holes” in the fan case assembly, but several fan blades adjacent to the fractured one in both directions had been damaged and all fan blade airfoils “had a combination of impact damage, tears, missing material” and had been bent in the direction opposite to rotation. A large quantity of bird remains (snarge) was found on the forward acoustic liner mainly “at the bottom of the fan case assembly and at multiple locations on the fan exit guide vanes” and samples were taken and sent for specialist analysis.
When no signs of any obvious flammable fluid leak sources were found, an on-wing fuel leak test was carried out by operating the aircraft’s right wing tank boost pumps to provide pressure and fuel was then seen “coming from behind the fuel-oil heat exchanger and the fuel-oil cooler generator located on the left side of the engine”. The test was stopped due to the large quantity of fuel leaking and since it had been impossible to identify the source(s) of the leak(s), the engine was removed from the aircraft and returned to the manufacturer Pratt &Whitney for further evaluation of its condition.
Looking into the damaged engine showing the position of the fractured missing blade. [Reproduced from the Official Report]
There, it was found that the leak had been coming from a fuel tube which had fractured as a result of vibration/cyclic loading generated by the loss of the missing fan blade following bird impact. Testing showed that there had been no pre-existing weakness underlying any of the damage caused directly or indirectly by the bird ingestion.
Expert examination of the bird remains identified them as from an immature male Bald Eagle with a mean mass of about 4.13 kg, above the 2.75 kg test bird weight used for engine certification purposes based on the size of the inlet throat area on the PW1100 engine. A review of the results of the large bird ingestion certification test results found that only sections of airfoil material from several blades with no full blade release like the one which had occurred in the event under investigation. Also, because the test was carried out using a test rig rather than a complete engine, the components which were damaged were not installed so “no comparison could be made”.
It was considered that the engine containment fan blade out certification test was arguably more relevant to a situation which had only been made potentially hazardous by the impact destruction of a fan blade. It was found that the fan blade out test had identified two fuel leak locations, neither of which was the result of damage to the fuel tube which had caused the leak after the bird ingestion blade release and the fuel leaks which did occur did not result in an under-cowl fire.
In respect of the ignition of the leaked fuel after the bird strike, although the hot brakes had reached a high enough temperature to cause ignition, the dripping fuel from the bottom of the nacelle had not been close enough to them ignite the fuel vapour present and even if the fuel vapour had reached the brakes, “it was unlikely to be at a concentration sufficient for combustion”. The only other ignition source was therefore the various engine case temperatures and it was concluded that the turbine intermediate case, the low pressure turbine case and the turbine exhaust case, all of which were downstream of the fractured fuel tube, would have been at temperatures “sufficient to support hot surface ignition of the leaking fuel”.
The Probable Cause of the investigated event was determined as "the ingestion of a bird into the right engine during the takeoff roll triggering a rejected takeoff and causing a fan blade to fracture near the blade platform resulting in high fan blade off loads and engine vibrations sufficient which resulted in an eventual failure of a fuel tube in the right engine that sprayed fuel onto hot engine cases, igniting an under-cowl engine fire”.
Editors Note - the word order in the text immediately above has been slightly modified in the light of FDR data included in the corresponding docket which shows that the fire warning only occurred after the aircraft had completed its rejected takeoff - as seen on the graph on page 7 of the Investigation’s ‘Engineering Factual Report’.
Safety Action being taken by International Aero Engines (IAE) in the light of this and other PW 1100 geared turbofan engine bird strike events was noted as a redesign of the fan blades which will include “thickening of the fan blade leading edge root, modifying the fan blade leading edge sheath to account for the thicker leading edge root, increased bonding area for the modified leading edge sheath and changes to the blade platform geometry”. The redesigned fan blade is expected to be available in 2023 and further action to directly address the fuel-fed fire risk by better protecting the integrity of the fuel tube is also being developed although final design details and the timing of for this was not known before the investigation of this event was completed.
The Final Report was published on 5 July 2022. No Safety Recommendations were made.
