The Accident Investigation Bureau (AIB) was not officially notified but got to know of the serious incident the following day, 6th June, 2015 through the media. Relevant authorities and stake holders were appropriately notified thereafter.
On 5th June, 2015, Aero Contractors Company of Nigeria Ltd. scheduled commercial flight NIG181, a Boeing 737-500 aircraft with registration number 5N-BLE from Lagos to Kaduna, took off at 1828hrs with 108 passengers and 5 crew on board. The First Officer was the pilot flying. The flight operated on an Instrument Flight Rules (IFR).
The Air Traffic Control (ATC) cleared the aircraft for takeoff and to climb and maintain Flight Level (FL) 350. Normal cabin rate of climb (300ft/min) was observed during the initial climb. During climb at approximately 23 minutes, the cabin altitude warning horn sounded and the cabin altitude warning light came ON.
The Captain took control of the aircraft, passenger announcement was made and emergency descent initiated to an altitude of 10,000ft.
The flight diverted to Abuja with a distance of about 120nm to go. The aircraft made a safe landing in Abuja at 1932hrs and all passengers and crew disembarked normally and without injuries.
The incident occurred at night.
The investigation identified the following causal and contributory factors:
The inadvertent failure to discover that the PRSOV was in the LOCKED CLOSED position after the engine change.
Failure to recognise that the number 2 bleed pressure was zero after engine start and subsequent failure to monitor the pressurisation system during climb.
One Safety Recommendation was made.