Description

On 27 November 2010, an Ilyushin IL-76TD (4L-GNI) being operated by Sunway Air Carrier (Georgia) on a non-scheduled international cargo flight from Karachi to Douala, Cameroon via Khartoum caught fire and crashed shortly after take-off in night VMC. The aircraft was destroyed by ground impact and a post crash fire. All six flight crew on board were killed.

Investigation

An Investigation was carried out by the Pakistan Safety Investigation Board (SIB). Relevant data was successfully recovered from the FDR for use in the Investigation by the MAK but the same agency was unable to obtain any data for the Investigation from either of the two CVRs installed on the aircraft due to their accident-damaged condition after recovery from the wreckage.

The 6 man flight crew of the aircraft was as follows:

• the Captain, born 1953, who held a Ukrainian Licence and had accumulated 7,272 total flying hours which included 5,502 hours on type
• the First Officer, born 1964, who held a Ukrainian Licence and had accumulated 2,220 total flying hours on all types but for whom type experience was not provided
• the Navigator, born 1961, who held a Ukrainian Licence and had accumulated 6,350 total flying hours in that role which included 4,800 hours on type
• the Flight Engineer, born 1968, who held a Ukrainian Licence and had accumulated 3,391 total flying hours on types which included the IL-76
• the Flight Radio Operator, born 1959, who held a Ukrainian Licence and had accumulated 3,393 total flying hours which included 3,334 hours on type
• the Flight Operator who held a Russian-issued "Flight Operator's Licence" and had 4,870 hours IL-76 experience.

It was established that the flight was carrying humanitarian aid in the form of tents which weighed 30.5 tons and with "about" 74 tons of fuel on board. It was calculated to have had a TOM of approximately 197 tons. The absence of a definitive TOM was attributed to the lack of "exact data about the fuel remaining after arrival at Karachi earlier in the day". The estimated take-off weight was between 5 and 7 tons above the applicable MTOM and it was considered that the delay in initiating rotation for take-off until the speed was 19 knots above Vr may have been intentional and if so indicative of crew awareness of an overweight take-off.

FDR data showed that an uneventful take off from runway 25L was quickly followed by failure of the No 4 engine. The available evidence indicated that this failure was uncontained and that it was debris ejected from the engine which caused impact damage to the right wing. Video evidence available to the Investigation indicated that it was the ignition of fuel/fuel vapour which started the observed wing fire. After reaching a maximum recorded height of 600 feet, the aircraft began to descend with a progressively increasing right bank before crashing right wing first onto an unoccupied construction site slightly to the right of the extended runway centreline approximately 2 nm from the airport at a speed of about 160 knots. The in-flight fire immediately intensified and almost the entire aircraft structure was destroyed.

It was concluded that impact debris from the engine failure had also damaged the flaps on the right wing which were still at the 30° take-off setting and that this damage, which worsened as the fuel fed fire continued, had reduced lift on that wing to the extent that "even full application of corrective flight controls" had been insufficient to control the increasing right bank.

It was noted from FDR data that this engine had been difficult to start prior to previous flights with the likely occurrence of hung starts which had been interrupted. When preparing for departure on the accident flight, it was noted that the crew had started the No. 4 engine (only) with the engine anti ice 'on', even though this was not required in the prevailing environmental conditions. The engine anti ice was selected off again after a successful start. It was concluded that "the most probable reason of abnormal starts of the No. 4 Engine was reduction of compressor efficiency because of wear of blades". This conclusion was based on the known reduction in compressor efficiency due to blade wear/roughness increasing both axial and radial clearances and the fact that the effect of heating mode on the inlet guide vanes is to increase the amount of air passing through the first stages of the compressor thus improving start reliability. It was considered probable that the No 4 Engine had remained in service despite having significantly worn compressor blades.

A failure by the aircraft crew to complete a routine R/T transmission as the aircraft climbed through approximately 300 feet was found to correspond to indications from FDR data of the likely initiation of the accident sequence. Mathematical modelling concluded that after the engine failure, some flight control inputs were no longer capable of producing the expected movement of their corresponding flight control surface. In the absence of any other information which would support different explanations for the loss of control, the Investigation therefore focussed on the failure of the No 4 engine and its consequences.

A series of fragments from the No 4 Engine were found below the flight path. Those from the LP compressor second stage disc were nearest the runway leading to the conclusion that it had probably been the origin of the failure. All of this debris only showed signs of mechanical damage in addition to evidence of thermal / fire damage. A detailed assessment of the recovered engine parts made by engine manufacturer NPO Saturn concluded that the LP compressor second stage disc had failed which had been followed by overspeed of the LP turbine and the disintegration of its sixth stage disc. A fatigue crack found in the disc of the LP compressor second stage disc was found to have started from the extreme edges of a hole in the disc which is used to install the bushing for the compressor blade pins.

Previous failures of the same engine type were found to have been caused by fatigue fractures of the same LP compressor stage as a result of "fretting corrosion" in these holes. Comparative analysis of disc fractures in previous cases with the failure on the No 4 engine of the accident aircraft "showed that they were of similar character". Such failures had been addressed some 25 years ago in IL-76 aircraft operating in the Russian Federation. However, since the Engine Log Book was not provided to the Investigation by the Operator, implementation of the remedial measures promulgated could not be established. According to the engine manufacturer NPO Saturn, this issue "is checked every time during life prolongation". However, it was found that the airframe manufacturer's "assigned calendar-based service life" for the accident aircraft had expired in May 2004. Thereafter, operation of the aircraft had continued without manufacturer approval. It was also found that all four of the accident aircraft engines were being operated beyond the service life established by their manufacturer without any life extension approval and that serial numbers of various components installed on the No 4 engine "were not the same as they should have been according to the information available in the engine documents".

The Cause of the Accident was formally determined as "failure of the 2nd stage disc of LP compressor of Engine No 4 due to a fatigue fracture which resulted in an in-flight fire and damage to adjacent areas of right wing / flaps to the extent that flight could not be sustained". It was also determined that "the use of the engine which failed beyond its manufacturer’s assigned life without assessment and life enhancement by the manufacturer was the cause of its uncontained fatigue failure".

A total of 14 Safety Recommendations were made as a result of the Investigation as follows:

• that All Operators and Ground Handlers should ensure preparation of a proper load / trim sheet while keeping within the maximum authorised allowable takeoff mass of aircraft / cargo loads for the specific type of aircraft.
• that the Georgian Aviation Administration should cooperate with the State of Design when putting an aircraft onto the State Register and issuing an Airworthiness Certificate. Notification of the inclusion of an aircraft on the State Register must be provided and the continuing airworthiness of the aircraft and its engines must be determined in accordance with the requirements applicable to the type of the aircraft.
• that the Aviation Regulatory Authorities of States which have the IL-76TD aircraft on their public register or on lease by their airlines should organise a check of the log books of the aircraft's D-30KP engines. Such checks must ensure that life limits, records and documentation are in conformance with Bulletin No 670-BE-G dated 8 February, 2002. The results of these checks should be coordinated with NPO Saturn, the manufacturer of the engines.
• that the Civil Aviation Regulatory Authorities of the States which have the IL-76TD aircraft on their public register or on lease by their airlines should organise a check of the IL-76TD aircraft log books for following:
  • observance of the assigned life limit until the first overhaul
  • the presence of life limit prolongation Permits (Conclusions) issued by Ilyushin until the first overhaul in accordance with the applicable Bulletins on the subject
  • the conformity of the issued (available) airworthiness certificates data to the assigned life limits until the first overhaul
  • the results of these Checks to be coordinated with Ilyushin and NPO Saturn, the manufacturer of the installed D30KP engines.
• that Airline Managements should ensure that a thorough check is made of aircraft and technical log books for correctness of records and trustworthiness of the life limits data while following the procedure of the inclusion of an aircraft in their Air Operator's Certificate. Moreover, required data as desired by investigation agencies should be provided.
• that Airline Managements should ensure that, at the time of delivery of the aircraft from the owner to the airline under lease arrangements, the complete aircraft and technical documentation is delivered to the Operator. The management of Independent Certified Maintenance Organisations must ensure the availability of all applicable technical documentation, correctness of records and trustworthiness of the life limit data of any aircraft maintained by such an organisation.
• that the Civil Aviation Regulatory Authorities of States which intend to include the IL-76TD aircraft in their public register should first make a thorough check of the contents of the aircraft and engine log books and the life limit data. The final decision of the inclusion in the public register should be taken only after the coordination with the airframe and engine manufacturers (Ilyushin and NPO Saturn).
• that the Civil Aviation Regulatory Authorities of States should ensure that the continuing airworthiness aspects of the aircraft included in their public register are in accordance with Annexes 6 and 8 to the Convention on International Civil Aviation. Special attention should be paid to the airworthiness status of such aircraft which are operated outside the State of Registry.
• that the Civil Aviation Regulatory Authorities of States should ensure that in the event that non-conformity or the violation of aircraft / engine life limits or Time-Between-Overhaul (TBO) prolongation procedure is identified, operation of affected aircraft must be stopped immediately.
• that the Pakistan CAA should ensure proper preservation of all available evidence collected during the process of investigation until the investigation concerned has been finalised.
• that the Civil Aviation Regulatory Authorities of States should ensure the institution of and compliance with flight crew training on emergency procedures related to engine failure during takeoff.
• that NPO Saturn should conduct a one-time inspection of the LP compressor 2nd and 3rd stage aft and fore ledges using the vortex-current method under the procedure prescribed by Bulletin No 578BD-G.
• that the Aviation Administration of the Kirghiz Republic should perform a check of the conformity of the maintenance company 'Airline Transport Incorporation FZC' Osh branch with the Certificate Regulations.
• that NPO Saturn as the designer and manufacturer of the D-30КP engine should introduce a form of engine marking that provides a unique serial number for each engine.

The Final Report of the Investigation was released on 3 March 2017.

Related Articles

• Uncontained Engine Failure
• Engine Failure During Takeoff - Multi-Engine Transport Category Jet Aircraft
• Wing Fire
• Loss of Control
• Continuing Airworthiness
• Maximum Take-Off Mass (MTOM)
• Aircraft Load and Trim