Event Details
On September 13, 2014, at approximately 06:02 UTC, a Felix Airways Bombardier CRJ702ER Next Generation, registration 7O-FAB, experienced a failure of the No. 1 (left) engine shortly after takeoff from Hodeida International Airport (HOD), Yemen. The flight, scheduled as flight 171 from HOD to Sana'a International Airport, was under normal takeoff procedures when the flight crew received a No. 1 engine fire warning indication accompanied by high N2 vibrations. The crew executed an inflight shutdown of the affected engine and performed an uneventful air turn back, landing at HOD without further incident.
Engine Damage Examination
After landing, operator personnel observed damage to the turbine blades, holes in the low pressure turbine (LPT) case, and holes in the aft cowl. The No. 1 engine required replacement. External examination of the engine revealed a breach in the LPT case measuring approximately 26½ inches circumferentially from the 6:30 to 11:30 o'clock position, just aft of the forward flange. The edges of the breach showed thermal/melting distress, and nearby components—including igniter cable anti-chaffing sleeves, electrical leads for the operability bleed valve, interstage turbine temperature (ITT) probes, and the No. 5 bearing oil supply tube—exhibited melted material.
Disassembly of the engine uncovered a 10-inch burn-through hole in the combustion chamber inner liner panels Nos. 2 and 3, spanning from the 10:30 to 00:30 o'clock position (aft looking forward). The combustion chamber outer liners had multiple linear axial cracks emanating from cooling holes, along with burned and melted material. The most severe thermal damage was located on outer liner panels Nos. 2 and 3, coinciding with the inner liner burn-through. Downstream of the combustion chamber, both the high pressure turbine (HPT) and low pressure turbine exhibited thermal distress and impact damage.
Testing and Research
Debris resembling brown soft talc collected from the HPT aft shaft and HPT stage 2 blade retainers was analyzed by General Electric (GE). The debris was consistent with Middle Eastern dust, and the chemistry and particle size distribution of two samples were nearly identical. One sample lacked carbonate minerals and was enriched with calcium sulfate, which GE attributed to exposure to sulfur dioxide from combustion, forming a calcium-magnesium-aluminum-silica (CMAS) compound. According to GE, CMAS melts on the thermal barrier coating (TBC) of combustion liner surfaces, infiltrates the TBC structure, contributes to early spallation, and accelerates thermal deterioration.
Fuel nozzles were flow-tested and, while not meeting all new/overhaul flow requirements, exhibited no significant fuel streaks or spray angle deviations. GE characterized the overall condition as typical for in-service units. HPT stage 1 and 2 blades showed significant thermal distress including melting, consumed material, and missing coating. Metallurgical examination indicated that these parts experienced temperatures above their intended maximum design point and material capability.
Testing of both upper and lower ITT harness assemblies revealed that they were not capable of accurate, reliable, and stable temperature readings in the post-event state. Due to thermal damage, the harness manufacturer could not determine whether erroneous temperature values were present before the engine fire or resulted from the event.
Operational Context
A review of engine trend data starting in early May 2014 showed a decrease in ITT (indicating cooler operation), a slight decrease in fuel flow, and a slight increase in core speed compared to a baseline CF34-8C5B1 engine. Felix Airways engineers noticed a significant difference in ITT between the event engine (position No. 1) and the sister engine (position No. 2), with the sister engine reading 20°C to 50°C higher. Felix Airways informed GE and requested guidance. GE expressed concern over the low ITT readings on the event engine and suggested borescope inspections for both engines and troubleshooting of the temperature indication system. The engine logbook for the event engine contained no record of such inspections or troubleshooting after May 2014.
At GE's request, the Safety Board reviewed removal rates for CF34-8C5/8E engines in harsh versus non-harsh environments (harsh defined as operating in certain countries including Yemen). Engines in harsh environments typically had shop visits between 3,000–3,500 cycles, while those in non-harsh environments visited shops near 9,000–10,000 cycles. At the time of the event, the engine had accumulated 8,010 flight hours and 9,347 cycles since its last shop visit—approximately 2.5 times the average for a harsh environment before removal. The calculated average flight leg was about 51 minutes.