CFM International CFM56 - Engine Failures

Engine Failures

Although the CFM56 is a very reliable engine (CFMI state that there is only one in-flight shutdown every 333,333 hours), there have been several engine failures throughout the life of the CFM56 family which were serious enough to either ground the fleet or require aspects of the engine to be redesigned.

Rain/hail ingestion

There are several recorded incidents of CFM56 engines flaming out in heavy rain and/or hail conditions, beginning early in the CFM56's career. In 1987, a double flameout occurred in hail conditions (the pilots managed to relight the engines), followed by the TACA Flight 110 incident in 1988. Both CFM56 engines on the TACA 737 flamed out while passing through hail and heavy rain, and the crew was forced to land without engines on a grassy levee near New Orleans, Louisiana. CFMI modified the engines by adding a sensor to force the combustor to continuously ignite under those conditions.

In 2002, Garuda Indonesia Flight 421 had to ditch into a river because of hail-induced engine flameouts, killing a flight attendant and injuring dozens of passengers. Prior to this accident, there were several other incidents of single or dual flameouts due to these weather conditions. After three incidents through 1998, CFMI made modifications to the engine to improve the way in which the engine handled hail ingestion. The major changes included a modification to the fan/booster splitter (making it more difficult for hail to be ingested by the core of the engine) and the use of an elliptical, rather than conical, spinner at the intake. While these changes did not prevent the 2002 accident, the investigation board found that the pilots did not follow the proper procedures for attempting to restart the engine, which contributed to the final result. Recommendations were made to better educate pilots on how to handle these conditions, as well as to revisit FAA rain and hail testing procedures. No further engine modifications were recommended.

Fan blade failure

One issue that led to accidents with the CFM56-3C engine was the failure of fan blades. This mode of failure led to the Kegworth air disaster in 1989, which killed 47 people and injured 74 more. After the fan blade failed, the pilots mistakenly shut down the wrong engine, resulting in the damaged engine failing completely when powered up after descent. Following the Kegworth accident, CFM56 engines fitted to a Dan-Air 737-400 and a British Midland 737-400 suffered fan blade failures under similar conditions, although neither incident resulted in a crash or injuries. After the second incident, the 737-400 fleet was grounded.

At the time it was not mandatory to flight test new variants of existing engines, and certification testing failed to reveal vibration modes that the fan experienced during the regularly performed power climbs at high altitude. Analysis revealed that the fan was being subjected to worse than expected high-cycle fatigue stresses, causing the blade to fracture; and more severe than tested for certification. Less than a month after grounding, the fleet was allowed to resume operations once the fan blades and fan disc were replaced and the electronic engine controls were modified to reduce maximum engine thrust to 22,000 lbf (98 kN) from 23,500 lbf (105 kN). The redesigned fan blades were installed on all CFM56-3C1 and CFM56-3B2 engines, including over 1,800 engines that had already been delivered to customers.