On 27 July 2006, a Bombardier CRJ200 being operated by Air Nostrum on a scheduled passenger flight from Barcelona to Basel, Switzerland in night Visual Meteorological Conditions (VMC), suffered a sudden left hand engine failure and an associated engine fire when passing FL235 some 14 minutes after take off. An air turn back was made with indications of engine fire continuing until just three minutes before landing. An evacuation using the right hand exits was ordered by the Captain as soon as the aircraft had come to a stop and had been promptly actioned with the Rescue and Fire Fighting Services in attendance. There were no injuries to the 48 occupants during the evacuation and the only damage was to the affected engine.
An Investigation was carried out by the Comisión de Investigación de Accidentes e Incidentes de Aviación Civil (CIAIAC) aided by the successful recovery and playback of Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) data.
It was established that with the First Officer as PF, the audible detected sound of engine failure had been rapidly followed by flight deck indications of left engine low oil pressure and fire and by annunciations of left engine thrust reverser unlocked and of toilet compartment smoke. ATC had been advised of an emergency situation and a return to Barcelona requested with radar vectors although this request was not met and a VOR/DME procedure was given. There had been no delay and the Rescue and Fire Fighting Services had been alerted in good time but it was considered by the Investigation that the ATC Service had failed to keep communications concise and thus contributed to the level of “agitation” of the already busy flight crew whilst the engine fire warning was continuing. Fortunately, the crew had had the airfield in sight once they turned towards it which avoided what might otherwise have been an avoidable increase in flight deck workload.
It was considered that whilst the flight crew had handled the emergency “adequately and without any consequences for the passengers” there were aspects of their performance which had not been in accordance with procedure. The emergency had been advised informally without the use of MAYDAY and the slightly uncoordinated initial response had evidenced poor Crew Resource Management with the resultant workload imbalance leading to the Captain taking over as PF. He had then, contrary to SOPs, disconnected the AP. During the approach, the applicable single engine checklist had not been fully completed and as a result, the flap override selection had not been made with the result that the correctly selected 20° flap setting had triggered five successive Mode 4B GPWS/TAWS alerts shortly before touchdown, which had not elicited any crew comment or response but would have required a go around had Instrument Meteorological Conditions (IMC) prevailed.
The contained failure of the GE CF34-3B1 engine was eventually found to have been caused by fatigue failure of a fan blade attributable to details of the manufacturing process being used at one of the four approved suppliers. Consequent vibration caused secondary damage and was considered to have led to the loss of both upper and lower fan access cowls (which were not recovered) and to the annunciation of a reverser unlocked warning (although it did not deploy) and, probably, the toilet smoke warning which had also been activated. The fire which started and continued occurred in the accessory gearbox compartment and burned through the fire seal into the aft compartment. The Investigation was unable to conclusively determine the origin of the fire but concluded that it continued because it was fuel fed due to the failure of the crew to select the failed engine thrust lever from idle to fuel cut off.
The in-service blade failure was the first to have occurred to the CF34 -1/-3 engine type, but during the course of the Investigation, a second similar failure occurred to an aircraft being operated by Atlantic Southeast Airlines in the USA on 24 May 2007 en route at FL230.The mode of failure and the blade manufacturer were the same as in the earlier case but there was no fire. As a result of their concern “that the throttle gearbox retention screws cannot withstand the extreme vibration loads that result from an FBO event and that this could result in the loss of engine fuel shutoff capability” the National Transportation Safety Board (USA) (NTSB) issued the following Safety Recommendation on 5 March 2008:
- That Transport Canada require Bombardier to redesign the retention feature of the Canadair Regional Jet-100/-200 aircraft engine throttle gearbox to ensure that it can withstand the loads generated by a fan blade separation or similar event. (A-08-03)
In respect of the flawed blade manufacturing process and the secondary damage risks at failure, the NTSB issued six further Safety Recommendations on the same day that The FAA:
- Require GE Aviation to define a reasonable maximum cycle limit below 4,717 cycles since new for Teleflex-manufactured CF34-1/-3 fan blades, considering the two failures and available data, and require that the blades be removed from service before that limit is exceeded. (A-08-04)
- Require GE Aviation to include dwell time fatigue testing in the CF34-1/-3 fan blade manufacturing process requirements to verify that any modified manufacturing process adequately reduces the possibility of the presence of aligned alpha colonies in the finished part. (A-08-05)
- Require GE Aviation to make modifications to the CF34-1/-3 engine design and ensure that an engine (imbalance) event will not cause the engine to catch fire. (A-08-06)
- Require GE Aviation to revise the CF34-1/-3 engine manual so that it clearly specifies the aft actuator rod hose elbow orientation and the requirement for adequate slack in the hose. (A-08-07).
- Require a one-time inspection of the aft actuator rod hoses installed on all CF34-1/–3 engines to ensure hose integrity during an (imbalance) event. (A-08-08)
- Require that all operators of Bombardier Canadair Regional Jet-100/-200 airplanes incorporate Bombardier’s redesign of the engine throttle gearbox retention as recommended in Safety Recommendation A-08-03. (A-08-09)
The explanatory letters issued by the NTSB with their Safety Recommendations to both Transport Canada (A-08-03) and the FAA (A-08-04 to A-08-09) are accessible under ‘Further Reading’ and contain detailed technical discussion not published by the CIAIAC. Appropriate Safety Action was taken by GE to “reduce the aluminium content of the material used to manufacture the blades and to control the wear and replacement of the tools used to machine the tangs that attach the blade to the fan dusk”.
The formal conclusion of the Investigation was that:
“The failure of the left engine (on the subject aircraft) was caused by the separation of one of the fan blades resulting from dwell time fatigue cracks that initiated from areas of aligned alpha colonies in the titanium microstructure that resulted from the blade manufacturing process.”
The Final Report was approved on 7 October 2010. In the light of the seven NTSB Safety Recommendations noted above made following the similar failure to a US-operated CRJ 200 and attributed to the same reasons, no further airworthiness action was considered necessary but one Safety Recommendation was issued as a result of the Investigation in respect of aircraft operation:
- That Air Nostrum reinforce its technical crew training in the following areas:
- Leadership and techniques for deliberate decision-making in abnormal and emergency situations.
- Crew task distribution in abnormal and emergency situations.
- Standards and procedures for fault identification, notification and prioritisation in abnormal and emergency situations.
- Strict compliance with procedures in abnormal and emergency situations so as to avoid inducing uncertainty in other crew members.
- The appropriate use of automation in every situation.
- The use of standard terminology in abnormal and emergency situations. (REC 03/10)
NTSB Safety Recommendation