What happened
On June 7, 2014, a Jet Airways ATR 72-212A, registration VT-JCS, was taxiing at Hyderabad after completing a flight from Rajahmundry. During the taxi phase, cabin crew noticed a strong smell of electrical wires accompanied by thick white smoke emerging from the mid-cabin area. Simultaneously, the flight crew received an electrical smoke warning in the cockpit.
In response to the escalating smoke, the pilots executed emergency checklists and shut down the engines. Because the source of the smoke could not be identified and the smoke continued to intensify, the captain coordinated with Air Traffic Control to evacuate the 62 passengers via the aft door on Taxiway B4. All passengers were safely deplaned without any injuries.
The investigation
An investigation by the AAIB examined the aircraft's systems and engine components. While external inspections showed no signs of fire or structural damage, borescope inspections of the engines revealed dried oil stains on the vanes of the left-hand engine HP impeller.
Subsequent detailed strip examination of the engine was conducted. Investigators found that while the core engine showed signs of standard operational wear and tear, specific hardware failures were present. The investigation focused on the air supply systems used for bearing cavity sealing and the condition of the engine's internal seals.
Findings
- The primary cause of the smoke and odor was inadequate air supply across the bearing seal.
- The P2.5/P3 air switching valve was found to be sticky due to service wear and tear, which prevented sufficient air pressure from being maintained.
- Deteriorated packing on the #4 bearing housing allowed oil to seep into the P2.5 air system.
- This oil seepage contaminated the air supply, resulting in the thick white smoke and the characteristic smell observed in both the cockpit and cabin.
Safety action
To prevent a recurrence, the following actions were recommended:
- The operator should perform visual inspections of the Air Switching Valve during Hot Section Inspections (HSI) and ensure overhauling during engine overhauls.
- Line maintenance personnel should be better trained to identify signs of core engine deterioration during borescope inspections.