Investigation Summary
The accident was traced to a fatigue crack originating from multiple corrosion pits in a Hamilton Standard propeller blade. These pits were caused by chlorine contamination during the manufacturing or refurbishment process. The specific blade had been rejected during an ultrasonic inspection in May 1994 but was subsequently refurbished at a Hamilton Standard facility. During this refurbishment, the technician incorrectly sanded the blade to remove the corrosion, failing to eliminate the deep pits and instead smoothing them over, which made them undetectable by visual inspection. The blade was returned to service and installed on N256AS in September 1994. Beyond the mechanical failure, the NTSB investigation highlighted deficiencies in Crew Resource Management (CRM) training, noting that the crew's coordination during the emergency was hampered by the extreme noise and vibration. Additionally, the investigation found that air traffic controllers failed to relay critical emergency information effectively, and the FAA had failed to mandate recurrent on-wing ultrasonic inspections that might have detected the growing crack before the catastrophic failure.
Final Conclusions
The NTSB determined the probable cause was the in-flight fatigue fracture and separation of a propeller blade resulting in distortion of the left engine nacelle, causing excessive drag, loss of wing lift, and reduced directional control. The fracture was caused by a fatigue crack from multiple corrosion pits that were not discovered by Hamilton Standard because of inadequate and ineffective corporate inspection and repair techniques, training, documentation, and communications. Contributing factors included the failure of Hamilton Standard and the FAA to require recurrent on-wing ultrasonic inspections and the overcast cloud ceiling at the accident site.
Photographic Evidence (1)
Video Analysis
What Happened to Flight ASA 529? | A Wounded Bird | Mayday — A detailed look at the mechanical failure and the heroic efforts of the crew and passengers to survive the crash and subsequent fire of Flight 529.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Edwin Gannaway, age 45.
First Officer
Matthew Warmerdam, age 28.
Systems & Failure Modes
Hamilton Standard 14RF-9 Propeller
A four-blade propeller system. The failure of one blade caused an extreme imbalance that led to the deformation of the engine nacelle.
Engine Nacelle
The housing for the engine; its deformation following the propeller failure created massive aerodynamic drag, preventing the aircraft from maintaining level flight.
Cockpit Crash Axe
An emergency tool used by the First Officer to break the cockpit glass. The NTSB recommended redesigning these axes to be more effective for egress.
Interesting Facts
- 01The aircraft had accumulated 17,151.3 flight hours and 18,171 cycles at the time of the accident.
- 02The failed propeller blade had been previously rejected in May 1994 but was improperly refurbished and returned to service.
- 03The post-crash fire was intensified by a leaking oxygen bottle located behind the first officer's seat.
- 04First Officer Matthew Warmerdam used the cockpit crash axe to attempt an escape through the windshield; the axe's design was later criticized for being difficult to use.
- 05The flight attendant, Robin Fech, was commended for her exemplary handling of the emergency and passenger briefing.
- 06The official NTSB fatality count is 8; a 9th victim died 121 days after the crash, which is outside the 30-day reporting window for fatal injuries.
Safety Actions & Advisories
Propeller Inspection Mandates
The NTSB recommended that the FAA require recurrent on-wing ultrasonic inspections for Hamilton Standard 14RF propellers to detect fatigue cracks.
Maintenance Training and Documentation
Recommendations were made to improve manufacturer engineering practices, propeller blade maintenance repair, and corporate training regarding inspection techniques.
Crash Axe Redesign
The investigation led to recommendations for the FAA to evaluate and improve the design of crash axes carried in aircraft to ensure they are effective for emergency egress.
ATC Emergency Procedures
The NTSB recommended improvements in the relaying of emergency information by air traffic controllers to ensure flight crews receive timely and accurate airport data during emergencies.
CRM Training Enhancements
The Board recommended that ASA and other operators enhance Crew Resource Management (CRM) training to better prepare crews for high-stress, high-noise emergency environments.