Caspian Airlines T154 near Janat-Abad on Jul 15th 2009, uncontained engine failure
Last Update: May 22, 2019 / 19:13:01 GMT/Zulu time
Based on collected data and evidence and after extensive analysis by experts in the investigation team the main cause of the accident was determined to be an abrupt damage to the molecular structure of the first rotor disc of the LPC in engine #1 due to a fatigue-induced crack which caused part of the disc to break apart and destroy the engine. Loose debris from the disintegrating engine then impacted the aft fuselage, severing hydraulic lines of systems #1 and #3 as well as the fuel line of engine #2. As a result of hot hydraulic fluid coming into contact with fuel and oxygen and due to excessive heat in the impact area, a fire broke out which destroyed the control rods of the aircraft and further damaged aircraft systems.
- Lack of immediate action by crew in order to stop the problem on engine #1 from escalating and prevent further damage to aircraft
- The manufacturer had not shared a crucial technical directive about engine checks with Iranian operators in a timely manner
- The PIC did not adhere to company operational procedures and policy in relation to supervising the crew, their assigned roles and their training in aircraft operating limitations
- Loading excessive fuel on board the aircraft and commencing takeoff above MTOW
- Lack of timely communication with ATS units regarding the problem on board the aircraft
The aircraft was cleared to climb to FL340 along airway G208 and was climbing through through 28,800 feet MSL when the aircraft began to descend, subsequently deviated to the left of the airway, radar contact was lost about 90 seconds later and the aircraft impacted ground in a farm with more than +5G vertical acceleration creating a deep crater about 28 meters wide. The #2 (tail mounted) engine was found about 190 meters from the impact crater. All 168 people on board perished in the crash, the aircraft was destroyed, some of the farm's crop was destroyed too.
A captain under supervision (55, ATPL, 6,700 hours total, 240 hours on type) was pilot flying, a first officer (33, CPL, 1,850 hours total) was pilot monitoring. A flight engineer (28, F/E and CPL, 200 hours total as pilot, 320 hours as flight engineer on type) as well as the commander of the flight (53, ATPL, 10,700 hours total) occupying the observer's seat while supervising the captain under supervision completed the flight crew.
The IAAIB reported the FDR data reveal the left hand engine (#1) was operating at about 84% N1, 2470kg of fuel flow per hour (FF) and an EGT of about 600 degrees C during the climb. At 07:22:00Z the aircraft was climbing through 27840 feet, engine #1 was operating at 84.0% N1, 2400 kg of FF and EGT of 600 degrees C, 7 seconds later (the onset) the parameters changed to 99.3% N1, 2333kg FF and EGT of 600 degrees C, accelerated further to 120.7% N1 with FF decreasing to 1289 kg and EGT dropping to 575 degrees C, half a second later severe vibrations were indicated for the #1 engine, 3 seconds after the onset an engine fire warning activated, the FF continued to decrease and the EGT continued to drop, the thrust lever position however had remained unchanged so far. About 6 seconds after the onset the FF of the #2 engine increased to 6000kg (beyond limit), all thrust levers were pulled back to about 33%, however, the #2 FF increased to 6900kg with all other engine parameters remaining unaffected, engine #1 was continuing to roll down. Increasing right rudder input was provided starting 7 seconds after the onset, increasing right aileron input was also provided. However, as result of asymmetric thrust between engine #1 and engine #3 the aircraft rolled to the left reaching 33 degrees left bank 11 seconds after the onset, maximum right aileron input was reached, the aircraft rolled through 44 degrees left 14 seconds after the onset and continued to roll to 65 degrees left bank even though right rudder also reached maximum deflection, the FDR recording ended prior to impact.
The IAAIB annotated that as result of impact by engine debris a fire had broken out in the aft section of the fuselage, which could not be extinguished due to lack of fire bottles in that area.
The IAAIB analysed that due to the captain under supervision having less than 250 hours on type, the commander was not authorized to permit the captain in the left hand and first officer in the right hand seat. In addition, according to the CVR, the commander did not coordinate or provide instructions throughout the flight including at and after the engine failure, the instructor and commander could not be heard on the CVR.
The IAAIB analysed the left hand engine (as well as the tail mounted engine) had operated for 3,911 hours and 1,843 flight cycles after last overhaul and was scheduled for the next overhaul after another 1,089 hours of operation (5000 hours between overhaul), the right hand engine had operated 214 hours and 92 cycles after last overhaul.
Remains of the #1 engine were sent to Russia for examination. The Russian investigators (MAK, Interstate Aviation Committee) determined that a crack had developed in the first stage of the low pressure compressor during the last 12 flight cycles as result of fatigue in the defective structure of the Titanium alloy. This cause parts of the rotor disk to separate. In 2010 the engine manufacturer issued service bulletin 1891 and 1892 introducing non-destructive tests as well as requiring the low pressure compressor (LPC) to be replaced on all engines with more than 8000 operating hours as those LPCs were no longer considered airworthy. The engine manufacturer however had issued service bulletins 1664 and 1665 prior to the accident already, both had been issued only to Russian operators. 6 days after the crash the engine manufacturer issues the bulletin 1877 to all operators which essentially was the same as bulletin 1664 and 1665 requiring eddy-current and dye-penetrant inspections of the first two stages of the low pressure compressor every 150+30 flight cycles.
The IAAIB analysed that none of the aircraft systems had any issue prior to the failure of the #1 engine. The debris of the disintegrating #1 engine impacted the fuselage at frame #65.
This debris impact severed #1 and #3 hydraulic system lines losing both hydraulic systems.
The #2 engine fuel lines severed either as result of debris impact or due to the excessive vibrations. The crew did not shut the engine down hoping to maintain function of the #2 hydraulic system (and thus flight controls) by keeping the engine operative, as all other #2 engine parameters remained normal. This however caused and fueled a fire in the aft section of the fuselage. The fire caused the control rods connecting the control column to the hydraulic actuators to sever, therefore the crew could no longer operate the control surfaces and lost control of the aircraft.
This article is published under license from Avherald.com. © of text by Avherald.com.
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