What happened
Shortly after the aircraft departed and lifted off from the runway, the flight crew detected an abrupt and loud noise that was described as resembling a tire blowout but significantly louder. This sound coincided with the immediate failure of the number one engine. The crew responded by securing the affected engine and maintaining control of the aircraft. Rather than diverting to another airport, they remained in the local traffic pattern and executed a safe landing on the same runway from which they had departed.
The investigation
Following the landing, a thorough physical examination of the failed powerplant was conducted. Investigators discovered that the combustion chamber outer case, identified by part number 616315, had suffered a catastrophic structural failure. Metallurgical analysis revealed that the primary cause of the failure was low cycle fatigue. The fatigue crack originated at a bolt hole located on the rear flange and propagated forward through the material.
The crack continued to grow until it reached a critical length, at which point the remaining cross-section could no longer support the operational loads, leading to final fracture via tensile overload. Crucially, forensic analysis of the cracked area detected the presence of nickel-cadmium plating. This finding was significant because the case had been last replated approximately 5152 flight hours prior to the accident.
Findings
The investigation determined that the root cause of the fatigue failure was improper maintenance procedures. Specifically, the application of nickel-cadmium plating to the bolt holes violated established engineering standards. The Pratt & Whitney Engine Repair Manual 72-42-11 explicitly prohibits the use of nickel-cadmium plating on the front and rear case flange bolt holes. This prohibited plating likely contributed to stress corrosion cracking or altered the fatigue properties of the material, leading to the premature failure of the combustion chamber case.