NORRA AT72 enroute on Oct 30th 2021, smell of smoke in cockpit
Last Update: January 19, 2022 / 10:02:11 GMT/Zulu time
Finland's Onnettomuustutkintakeskus (AIBF) rated the occurrence a serious incident and opened an investigation. No injuries and no damage were reported.
On Jan 19th 2022 Finland's Onnettomuustutkintakeskus (AIBF) released their final report in Finnish only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a Finnish only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe). The report concludes the probable causes of the serious incident were:
1) The oily smell of smoke in the cockpit was due to leaks in an oil sealing in the left engine bearings. Oil was thus allowed to seep from the engine into an area, where air also enters the aircraft systems. The leak was partly to an air switching valve's wear (editorial note: explanation found in the analysis: the air switching valve permits air to seal the bearings from either the low or high pressure side depending on engine speed).
Smoke or smell of smoke in an aircraft in flight is some of the most critical phenomenas depending on its intensity. ATR-72-500 aircraft and others using similiar engines wear and tear on Air Switching Valves can lead to different oil spills. The Air Switching Valve is not part of the time controlled spare parts of the engine.
2) The cockpit smelled of oil on several occasions during the flight. The crew did not initiate the emergency checklists measures in accordance with the appearance of smoke or smell of smoke prior to the final approach.
Emergency checklists for smoke or smell of smoke and taking according action would have prevented the oily smell to enter the cockpit.
3) Emergency Checklists require the use of oxygen masks and the use of smoke goggles in smoke or smell of smoke situations first before any other action.
According to instructors the threshold for the smoke/smell of smoke emergency checklists is high especially in mild or unclear smell of smoke situations. In this case the actual measures to identify the source of the smell, correct the situation did not work out to prevent the situation on final approach.
4) Rescue services and air traffic control should instruct the crew to switch to ground frequency to directly communicate with the rescue services if necessary. This practise was not implemented, communication continued through air traffic control. The need for communication might also come from the rescue services.
Direct communication between the aircraft and rescue services can streamline the flow of information and improve situational awareness.
5) Airport rescue services were led by two different fire chiefs callsigns ARP30 and ARP40. Both were in contact with air traffic control and the aircraft during the situation.
Use of two rescue fire chiefs separately as leaders can hamper the overall management of the situation.
The AIBF analysed maintenance primarily examined the left engine because it supplies air conditioning to the cockpit. Traces of oil were found in the #5 gas generator casing (GGC) bearing at the rear of the engine. The air switching valve permits air to seal the bearings from either the low or high pressure side depending on engine speed. Uneven wear grooves might interfere with the operation of the valve's piston leading to valve failure resulting in insufficient pressure to seal the bearing. This in turn can cause oil to enter an area from which air enters the air conditioning system of the aircraft. The valve was replaced, the aircraft was testrun and found airworthy. The operation of the valve is not recorded by the QAR. The valve was not assigned a life time and thus was not a time controlled spare part.
During the flight, the pilots noticed a clear smell of smoke in the cockpit right at the beginning of the flight, for the second time mild at the end of the take-off flight and finally strong before landing. At all times however, the smell of smoke dissipated. Except for an observation prior to landing the crew did not initiate QRH emergency checklist actions. The threshold for the use of an oxygen mask and smoke goggles is high if there is no visible smoke and the smell of smoke is indistinct.
According to technical studies, the smell of smoke would have ceased in the cab if the air conditioning system 1 had been closed. As part of the air in system 1 goes into the cabin, there is smoke the smell must have ended up there as well. However, it has been so small that it was not observed in the cabin.
This article is published under license from Avherald.com. © of text by Avherald.com.
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