On 3rd January, 2019, at about 10:10 h. 2019, a Boeing 737-500 aircraft with registration marks 5N-AIS operated by Azman Air Services Limited on a scheduled commercial flight AZM 2316, departed Lagos for Port Harcourt on an Instrument Flight Rule (IFR) Flight Plan with 109 passengers and five crew on board. The fuel uplift was 8, 900kg. The flight was the first flight of the day for the aircraft. There was no reported technical fault or observation on both engines during the previous flight.
The take-off and climb out phase was normal. Captain was the Pilot Flying (PF) and Co-pilot was the Pilot Monitoring (PM). The aircraft levelled off at a cruising altitude of 29,000 ft (FL 290). According to the Flight Data Recorder (FDR), Engines No. 1 and No. 2 were both showing 84.6% N1 before the engine No 2 malfunction.
According to the flight crew, at some point during the cruise, about 20-25 minutes into the flight, they heard a loud bang which lasted for about 4-5 seconds followed by a yaw to the right. However, at about 10:28 h FDR data revealed that Engine No 2 N1 value start decreasing for about 4.3 seconds (which corresponds to the point at which the crew heard a bang and experienced a yaw).
The flight crew also stated that engine parameters look normal at that time and in addition, the Purser reported that there was nothing unusual noticed in the cabin after the loud bang. The flight crew therefore assumed that the bang was associated with cargo shift. The aircraft was on Autopilot (A/P) and Auto Throttle (A/T).
At about 10:42 h, Port Harcourt Approach cleared the aircraft for a straight in approach on runway 21; Flap 15o selected, Localizer captured, Glideslope captured and the gears were selected to DOWN position. As the A/P disengaged, the aircraft suddenly yawed to the right accompanied by severe vibration and also thrust asymmetry was noticed. At that time, Glide was two Dots below and field was NOT in sight. The PM noticed No.1 Engine vibration indicated 3.0 to 3.5 units, No.1 Engine N1 was 65%, No.2 Engine N1 was 35% and the No.2 Oil Filter Bypass Light came ON. This led to precautionary shut down of No 2 Engine by the crew.
FDR data also indicated that, at one point before the approach, the figure of engine instruments were indicating almost the same with no difference until about 10:53 h when the crew advanced the throttles individually in order to verify the engine out puts. At that time, the crew noticed that No 2 engine did not respond appropriately to the throttle movement. FDR data also indicated that No 2 Engine was shut down five minutes after the verification of the engine output.
In order to figure out what was happening, the Captain handed over control to the Co-pilot. The crew accomplished the Severe Engine/Damage Checklist. However, the first approach became unstable and the crew executed a Missed Approach at about 10:55 h.
At about 11:09 h, when the ATC cleared the crew for the second approach, the response was that they were not ready for approach at that moment. However, they requested for vectors as they were having problem with No 2 engine.
During the second approach to runway 21, the aircraft came high on the approach and was off track of the runway centreline. At about 11: 19 h, the crew declared emergency and executed a second missed approach. However, the crew were able to land the aircraft safely on runway 21 after the third approach at about 11:35 h.
The Airport Rescue and Fire Fighting Service (ARFFS) had already positioned its fire fighter on standby close to runway 21 in readiness of any emergency on the distressed aircraft. After landing, the aircraft taxied, exited the active runway and escorted to the apron where the occupants disembarked normally without any injuries.
The incident occurred in day time in an Instrument Meteorological Condition (IMC).