By Simon Hradecky, created Wednesday, Apr 19th 2017 23:36Z, last updated Tuesday, Jul 28th 2020 18:08Z

An Aerocontractors de Havilland Dash 8-400, registration 5N-BPU performing flight NG-316 from Port Harcourt to Lagos (Nigeria) with 53 passengers and 4 crew, was enroute at FL240 about 75nm east of Lagos when the crew received a cargo smoke indication and the cabin started to fill with smoke. The crew declared emergency, performed smoke removal procedures and continued to Lagos for a safe landing about 18 minutes after the smoke was noticed.

Nigeria's Civil Aviation Authority opened an investigation into the occurrence.

The airline reported that about 75nm before Lagos cabin crew observed the cabin was misty and informed the flight crew. The flight crew made an announcement re-assuring the passengers. Shortly after the descent into Lagos had been initiated about 10 minutes later cabin crew observed a passenger entering the aft lavatory, the smoke detector activated shortly afterwards and the smoke in the cabin became more dense, the crew received an aft cargo smoke indication, too. The flight crew performed smoke removal procedures while cabin crew handed out wet towels. The aircraft landed safely about 18 minutes after the first observation of mist. It was determined that the smoke actually originated in the cargo section and was distributed into the cabin by the air conditioning system. An inspection of the aircraft did not reveal any anomaly.

On Jul 28th 2020 Nigeria's Accident Investigation Bureau (NAIB) released their final report reporting:

"Accident Investigation Bureau (AIB) was not officially notified of the serious incident but got to know about it through social media on 19th April, 2017. AIB investigators were immediately dispatched to the Aero Contractors hangar in Lagos, where the aircraft was parked."

The NAIB concluded the probable cause of the serious incident was:

Engine oil leaked onto a hot surface of the engine causing fumes which mixed with the engine bleed air supply to the air conditioning system, resulting in smoke in the aircraft cabin, cockpit and lavatory/ cargo compartments.

The NAIB analysed:

Borescope Inspection on Engine No. 1 showed traces of oil around the Low Pressure Compressor stage 1 blades, Inter-Compressor-Case (ICC), Inter-Turbine Vane Struts and Gas generator area of the engine. Wetness was found at the Gas Generator Case, PT Stage 1 case and Low Pressure Turbine (LPT) blades. The bleed air for the air conditioning system is extracted from stage 5 or 9 of the compressor (as the case may be) through a bleed valve and mixes with hot air for the required temperature to achieve passenger comfort. The presence of smoke in the cabin and cockpit area can be attributed to this conditioned air.

The result of the Borescope inspection carried out by the Aero Contractors Company Ltd revealed that the source of oil leakage from No.1 engine could not be ascertained at the conclusion of the borescope inspection but the oil found in the shaft area of the compressor interchange CIS was suggestive of failure of either CIS carbon seal or any of the internal oil supply tubes. The pool of oil leak mixing with the engine bleed air resulted to smoke in the aircraft cabin, cockpit and lavatory/cargo compartments which contaminated the Air Conditioning system of the aircraft. The smoke had no smell or odour, was not irritating to the eyes and did not cause cough.

Considering a significant number of previous occurrences of smoke in the cabin was traced to oil leaks from the CIS Bearing Carbon Seals in DCH8-400, Pratt & Whitney Canada, being the manufacturer of the engine (PW150A), had designed upgraded Bearing Carbon Seal and recommended its installation via Service Bulletin 35342R1.

Furthermore, P&WC had developed a new oil analysis technology programme for the detection of impending seal failures and made it available to all operators whose engines were yet to comply with SB 35342R1.

The investigation revealed that this Service Bulletin was issued after this occurrence.

The crew have conducted the flight appropriately in accordance with the company procedures stipulated in Quick Reference Handbook and landed the aircraft safely with no damage or injuries. It was reported that the flight deck crew did not communicate effectively with the cabin crew and hence, there was poor coordination between the cockpit crew and the cabin crew throughout the duration of the emergency procedures.

Passenger video (Video: Uju Ayalogu):

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