On 6 March 2018, a Bombardier DHC8-400 (5N-BQJ) being operated by Arik Air Nigeria on a scheduled international passenger flight from Lagos, NIgeria, to Accra, Ghana, as ARA304 was in night instrument meteorological conditions (IMC) at FL 240 when smoke was detected entering the flight deck and passenger cabin from the air conditioning system. The corresponding drill was followed and an emergency was immediately declared requesting priority routing to an emergency landing at destination. In the event, the action taken led to the emergency being downgraded and a normal arrival followed.
The Nigerian Accident Investigation Bureau (AIB) was not informed of the occurrence of a Serious Incident by any of the parties involved and only became aware of it on seeing a social media post two days later. The Bureau then contacted the Ghana CAA as the State of Occurrence for clarification and subsequently opened an Investigation. Relevant data were obtained from the flight data recorder (FDR) but relevant data on the cockpit voice recorder (CVR) were found to have been overwritten because the CVR had not been isolated during maintenance inspection following the arrival in Accra. Statements by all crew members were available and were found to be consistent with each other.
It was noted that the 42-year-old Captain, a native of Antigua and Barbuda, had a total of 6,238 hours flying experience of which 2,360 hours were on the DHC8-400 which was his only multi-engine command experience. The First Officer, who was pilot flying (PF) for the flight under investigation, was a 29- year-old Nigerian national who had a total of 1,240 hours flying experience of which all but 200 hours were on type.
It was established that shortly after the flight had entered Ghanaian airspace about two-thirds of the way to Accra cruising at FL240, the First Officer had called the Captain’s attention to “misty air coming from the right side air vents” which, on further observation, both pilots confirmed to be smoke. At about the same time, the senior cabin crew member (SCCM) reported to the Captain that smoke was present in the mid section of the passenger cabin. The flight crew stated that they had immediately referred to the ‘FUSELAGE FIRE, SMOKE or FUMES’ quick reference handbook (QRH) procedure. The Captain then declared a MAYDAY to Accra APP stating that there was smoke in the flight deck and the passenger cabin and requesting a priority routing to destination for an emergency landing followed by an on-runway evacuation which was approved. The Captain reported having then given the SCCM a NITS brief and followed this with the delivery of a passenger briefing over the PA system. The cabin crew stated that in response to the smoke they had “distributed paper serviettes to passengers to cover their noses and mouths”.
After a while, the action taken by the crew led to the cessation of the smoke and so the emergency status was subsequently downgraded and the SCCM updated accordingly. A normal landing with the airport rescue and fire fighting services (RFFS) standing by subsequently followed after which the aircraft was taxied to its assigned gate for passenger disembarkation.
Why it happened
The aircraft was withdrawn from service and the applicable AMM procedure was carried out. An initial visual inspection of the right hand PW150A engine found that the P2.2 inter-stage valve exhaust was full of oil and that there were also signs of oil contamination in the generator case, the LPC (Low Pressure Compressor) and HPC (High Pressure Compressor), the air intake ducts and the P2.2 and P2.7 bleed air ducts. Traces of oil were also found in the air conditioning compartment in the tail of the aircraft.
These findings led, as required by the AMM, to a borescope inspection of the compressor inner support and the intercompressor case strut which found evidence of oil staining on the strut and its vicinity, oil stains within the vicinity of the LPC stage 1 blade and evidence of oil stains on the LPC stage 3 blade. It was noted that the oil level in the right engine oil tank was also found to be abnormally low. These findings were considered to point to a failed P2.5 bearing as the origin of leaked oil.
It was noted that cabin air contamination due to leaking engine oil had been a regular occurrence on the aircraft type involved over a number of years and as a result, Pratt & Whitney Canada (P&WC), as OEM had released an SB in 2016 detailing a “modification of the P2.5 bearing carbon seal”, one of the sources of such oil leaks and identified as such in the event under investigation. This SB was subsequently revised to required use of an upgraded seal in January 2018. Compliance urgency for this SB was rated as “category 6” with compliance recommended “when the subassembly (i.e. engine, module, accessories or component) is disassembled and access is available to the necessary parts when the engine is sent to the workshop’’.
In addition to this oil seal SB, the OEM also provided operators who had yet to carry out the recommended overhaul, with an “Oil Analysis Technology Program” to improve the detection and analysis of chemical elements or alloys in engine oil before they cause system failure.
The crew response
Although the flight crew stated that they had completed all actions in the QRH ‘Fuselage Fire, Smoke or Fumes’ checklist, it was found that this was not the case as they had assessed the situation and decided that having assessed the intensity of smoke/fumes entering the flight deck as “mere mist” such action was not necessary. It was noted that the reason this checklist item was not optional was because “the nature of smoke/fumes can only be assessed by chemical analysis or special equipment, neither of which is practicable in flight”.
It was noted that although the smoke/fumes had ceased following completion of the appropriate QRH procedure, the origin of the fumes remained unknown. Given this fact, it was considered that the Captain’s decision not to evacuate the passengers on landing and instead to taxi to the assigned gate for them to disembark “might have been a misjudgement” since in any instance of smoke in the flight deck or passenger cabin where the source cannot be positively determined, “there is a possibility that an uncontained fire could still be burning somewhere within the aircraft fuselage”.
It was noted that the requirements for pilot Safety and Emergency Procedures (SEP) recurrent training on the effect of smoke in an enclosed area and the use of relevant equipment in a simulated smoke environment was covered over a 3-year period and that “the use of emergency and safety equipment in a smoke environment should therefore be scheduled more frequently during simulator training”.
Finally, it was also found that the cabin crew had not properly executed their Fire Drill Checklist as detailed in their Safety & Emergency (SEP) Manual which was noted to state that “in the event of a lot of smoke in the cabin, passengers should be relocated (as necessary) and given wet cloth to breathe through”. The cabin crew’s distribution of dry serviette paper to cover their nose and mouth was considered to have “exposed the passengers to a high risk of irritation and suffocation”.
The Cause of the Serious Incident was determined as “engine oil leaking onto the hot surfaces of the engine No. 2 due to a failed seal which produced fumes that mixed with the bleed air supply to the air conditioning system and resulted in smoke in the aircraft flight deck and cabin”.
Two Safety Recommendations were made as a result of the Investigation as follows:
- that Arik Air Nigeria should ensure that flight crew execute appropriate checklist items completely in line with the aircraft FCOM and QRH. [2021-028]
- that the Nigerian Civil Aviation Authority should ensure that flight crew type-rated on the Bombardier DHC-8-Q400 should undergo further training on “The effects of smoke in an enclosed area and actual use of relevant equipment in a simulated smoke environment”. [2021-029]
It was noted that a further relevant Safety Recommendation had been made after an almost identical event involving another operator’s DHC8-400 had occurred in 2017 as follows:
- that the Nigerian Civil Aviation Authority (NCAA) should ensure that operators utilise the ‘New Oil Analysis Technology’ made available by Pratt & Whitney Canada in order to identify impending failure of the carbon seals on PW150A engines that do not to comply with SB 35342R1. [2019-25]
The current Investigation recorded the fact that on 19 December 2019, the NCAA had responded to this recommendation by advising the AIB that since the 2018 event, Arik Air had actioned SB35342 - as issued by Pratt & Whitney in 2016 but subsequently updated to SB35342R1 in 2018 - on 4 of their 6 DHC8-400 PW150A engines and were also “in the process of” amending their DHC8-400 Aircraft Maintenance Programme to include the proactive procedures of the new 'Oil Analysis Technology Programme' for all engines. It was noted that one of the engines on 5N-BKX had been modified in accordance with SB35342R1 at the time of writing but that the other was one of the two awaiting this modification.
The Final Report of the Investigation was published on 8 July 2021.