Merpati MA60 near Bima on Dec 12th 2011, engine fire due to fuel leak
Last Update: September 11, 2015 / 14:15:57 GMT/Zulu time
Indonesia's NTSC released their final report concluding the probable causes of the serious incident were:
The fire on the left engine was due to fuel leak on the fuel line fitting which was improperly tightened.
The delay of the pilot action had prolonged exposure the risk of the fire and jeopardize to the safety of the flight.
The NTSC reported that following landing an examination of the engine revealed evidence of fire at the bottom of the engine case below the hot and cold section of the engine. The fuel line underneath the fuel flow transmitter was found wet. The engine was cold cranked to increase the fuel pressure, a fuel leak was identified at the fuel flow transmitter at a rate of 21 droplets per minute as result.
The NTSC stated: "The original locking wire on the fuel fitting at the lower part of the fuel flow transmitter was intact. After opening the locking wire, the fitting was found to be not properly tightened. A further tightening could rotate the nut of about 5mm. After a retightening the fuel fitting, a cold cranking was performed and there was no fuel leak observed in the corresponding tube. There was no rework performed by the operator on the fuel flow transmitter. The installation of this particular fitting was performed by the aircraft manufacturer."
The NTSC reported that the flight data recorder stored 25 hours of data. Comparing the fuel flow of the occurrence flights with earlier flights it became apparent, that a discrepancy between left and right hand engine developed during the last 9 flights (including the occurrence flight) indicative of a fuel leak. The NTSC stated: "The fuel flow depends on the engine power setting. It reached its highest value at the take off stage, and it became smaller during climb. It is shown that the leak was at takeoff, and reduced gradually in the climb stage, and even ceased during cruise."
The NTSC analysed: "Fire initiated from the lower part of the cowling in front of the partition between hot and cold section of the engine number 1 where the fuel leak accumulated at that location. The fire moved upward crossing the frame bulkhead to the hot section."
The NTSC continued analysis: "During an inspection after the incident, the location of fuel leak was indicated at a tube and fitting which was found wet. The fuel leak was confirmed during cold cranking in which droplets of fuel leak observed at that location. The amount of fuel leak during cold cranking was also measured, i.e. 21 droplets per minute. During take-off the fuel pressure is much higher than during cold cranking. Therefore the fuel leak might be much larger during take-off and climb stage. The FDR revealed that the fuel flow difference reached up to 150 pph (pound per hour), or equivalent to 2.5 lbs/minute. During takeoff, the takeoff power was applied for approximately 2 minutes; therefore the fuel leak on the bottom of the engine contained approximately 5 lbs of fuel. Some part of the leaking fuel evaporated, and in the elevated temperature environment approaching the flash point a self-ignition could occur."
The NTSC analysed with regards to crew actions: "In this incident there was uncertainty in identifying the occurrence of fire. The fire warning was not immediately considered as the highest degree of warning. There was lengthy discussion between the pilots before a decision was made. This situation might arise from the fire warning that was not immediately perceived as engine fire. The pilot performed fire drill after the engineer informed that the fire on the left engine was visually observed. ... Discharging the fire extinguisher before shutting down the fuel supply would certainly un-effective to extinguish the fire. The incorrect sequence of the pilot actions indicated that the fire drill was not well pattern memorized. Schemata or mental model is a representation of the structure and operation of a system. Mental models are developed largely through experience, regular training and active interaction with the environment. The incorrect sequence could have been a result of insufficient pilot training, most specifically in in-flight engine fire."
This article is published under license from Avherald.com. © of text by Avherald.com.
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