What happened
On 5 February 2012, an IL-76TD cargo aircraft, registration RA76799, was taxiing on Runway 12 at Sharjah International Airport following a flight from Kandahar. During the taxi phase, the air traffic controller observed smoke and flames emitting from the exhaust of the number two engine. In response to the visible fire, the captain was instructed to halt the aircraft immediately. Emergency services responded, and fire extinguishers were deployed into the engine inlet. The aircraft was subsequently towed to a cargo stand, and no injuries were reported among the eight persons on board.
The investigation
The GCAA AAIS investigation focused on the mechanical failure of the engine and the operational factors surrounding the incident. Investigators examined the number two D-30KP-2 turbofan engine, finding significant damage to the turbine blades, some of which had disintegrated. The inquiry also reviewed the aircraft' and operator's maintenance records, fuel quality, and the functionality of the Fuel Control Unit (FCU). The investigation looked into the fuel supply chain, including the quality of fuel available at outstations and the effectiveness of the operator's fuel contamination monitoring systems.
Findings
Technical analysis revealed that the primary cause of the engine damage was fuel contamination that exceeded permissible limits. This contaminated fuel partially blocked a fuel nozzle, creating a flame torch effect. This concentrated flame caused extreme heat stress on the second-stage turbine nozzle guide vanes, leading to their structural failure. The disintegration of these vanes caused subsequent mechanical failure of downstream turbine components.
Additionally, the investigation identified several contributing factors:
- The Fuel Control Unit (FCU) was not operating correctly, resulting in improper fuel metering.
- The operator lacked a sufficient quality control system to audit fuel stations at outstations.
- There was an absence of an adequate engine inspection program capable of detecting fuel deposit accumulation in the nozzles.
- The crew may not have been aware of the rising Exhaust Gas Temperature (EGT) due to potential monitoring issues or cockpit indications.
Safety action
The investigation resulted in several safety recommendations directed at the operator, the Russian State Oversight Flight Safety Department, the Ilyushin Design Bureau, and the UAE GCAA. Key recommendations include:
- The operator should perform hot section inspections on similar engines within the fleet and enhance fuel system maintenance and inspection intervals.
- The operator must strengthen its quality management system to include more rigorous audits of fuel suppliers and fuel quality assurance.
- The Ilyushin Design Bureau and engine manufacturers should work to improve engine fuel system inspection procedures.
- The UAE GCAA was advised to expand its SAFA program to include fuel contamination checks for foreign operators.