What happened
On May 6, 2015, a Boeing 727-200F, registration HK4262, operated by Líneas Aéreas Suramericanas S.A, was performing a non-scheduled cargo flight from Bogotá (SKBO) to Quito (SEQM). Shortly after takeoff from runway 13R at El Dorado International Airport, the crew initiated the landing gear retraction. During this maneuver, a loud noise was heard coming from the number one engine.
Upon inspecting the cockpit instruments, the crew observed abnormal Exhaust Gas Temperature (EGT) readings on the number one engine. The crew immediately reduced power to the affected engine and notified Air Traffic Control to request an emergency return to Bogotá. The aircraft landed safely on runway 13L without further incident. The four crew members evacuated the aircraft on their own and were uninjured. No post-incident fire occurred.
During the initial climb, the number one engine expelled fragments of turbine disc blades. These fragments were later recovered by local residents, GRIAA investigators, and airport firefighters from rooftops near the threshold of runway 31L.
The investigation
The GRIAA investigation focused on the mechanical failure of the Pratt & Whitney JT8D-17 engine. Investigators identified fractures in the blades of the T4 turbine disc, which had subsequently caused fractures in the T1 and T3 turbine stations. While the engine components were within their established life limits, the investigation uncovered several maintenance discrepancies:
- The last borescope inspection for the number one engine had been performed on August 14, 2013. By the time of the accident, the engine had flown 839:32 hours since that inspection, exceeding the 600-hour interval required by the maintenance program by nearly 240 hours.
- There was a lack of traceability for the hours and cycles of the T1 disc between the years 2000 and 2007.
- Investigators found evidence of an unauthorized fiberglass repair on the engine's exterior C2 cover that did not comply with the manufacturer's maintenance manual.
Findings
- The primary cause of the engine failure was the fracture of a rotor blade at the first turbine station (T1), driven by stress and fatigue originating from areas previously affected by intergranular corrosion.
- The internal cooling passages of the T1 rotor blade were blocked by silicon contamination, likely caused by sand ingestion.
- A significant contributing factor was the failure to perform the required borescope inspection every 600 hours, as mandated by the engine maintenance program.