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ASN Wikibase Occurrence # 202557
Last updated: 25 November 2021
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Type:Silhouette image of generic B735 model; specific model in this crash may look slightly different
Boeing 737-522
Owner/operator:Aero Contractors
Registration: 5N-BLE
MSN: 26672/2343
Fatalities:Fatalities: 0 / Occupants: 113
Other fatalities:0
Aircraft damage: None
Category:Serious incident
Location:en route Kaduna Airport -   Nigeria
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Lagos-Murtala Muhammed International Airport (LOS/DNMM)
Destination airport:Kaduna Airport (KAD/DNKA)
Investigating agency: AIB Nigeria
Aero Contractors flight NIG181, a Boeing 737-500 aircraft, took off from Lagos, Nigeria, at 18:28 hrs local time with 108 passengers and 5 crew on board. The First Officer was the pilot flying.
During the initial climb, the Captain observed that the cabin rate of climb was zero but later indicated normal. However, the First Officer reported that on reaching FL150, he observed that the cabin altitude was indicating about 3000ft and since this occurred at low altitude, they decided to monitor during climb.
Approximately 23 minutes after becoming airborne and climbing through FL330, the cabin altitude warning horn came on and the Captain took control of the aircraft. The flight crew donned their oxygen masks, set the regulators to ON/100% and crew communication was established as required by the procedures of the approved Quick Reference Handbook (QRH) and Airplane Flight Manual (AFM).
According to the account of the purser, she went into the lavatory and observed that the sink was full, which she tried to drain. She got out of the lavatory and observed that her oxygen mask had dropped. She then checked the cabin area and observed that the business class passengers’ oxygen masks had also dropped. She immediately took her seat, donned her mask and briefed the passengers. Thereafter, she called the cockpit but there was no response.
Emergency descent to an altitude of 10,000ft was initiated. The Captain briefed the purser and made an announcement to inform the passengers that the flight was being diverted to Abuja.
The aircraft landed safely in Abuja at 19:32 hrs, taxied to the ramp and parked. Crew and passengers disembarked without injury.

On 5th June, 2015; the day of the incident, engine no.2 was changed at Lagos due low time remaining and replaced with another engine. The engine post-installation procedure required that the Pressure Relief Shut-Off Valve (PRSOV) should have been checked after the engine change to confirm that it is in the OPEN position. The engine installation procedure as contained in the AMM Section 71‐00‐02 requires a series of post-installation tests to verify correct operation. One of these tests is the Pneumatic Leak Test. This test requires that the PRSOV be manually wrenched to the OPEN position. The PRSOV will remain open when there is pneumatic pressure upstream of the PRSOV.
There is no evidence to show that these procedures were followed by the maintenance engineers during the engine installation. Also, there was no evidence that a duplicate inspection was carried out to confirm that appropriate procedure had been followed during the engine installation.

Causal Factor:
The inadvertent failure to discover that the PRSOV was in the LOCKED CLOSED position after the engine change.
Contributory Factor:
Failure to recognise that the number 2 bleed pressure was zero after engine start and subsequent failure to monitor the pressurisation system during climb.


Accident investigation:
Investigating agency: AIB Nigeria
Status: Investigation completed
Download report: Final report
Other occurrences involving this aircraft

21 Aug 2010 5N-BLE Aero Contractors Company of Nigeria Limited (ACN) 0 Jos Airport (JOS/DNJO) min
Runway excursion.
21 Mar 2021 5N-BLE Aero Contractors 0 near Kano-Aminu Kano International Airport (KAN/DNKN) unk
Bird strike.


Photo of 5N-BLE courtesy

Lasham (EGHL)
1 December 2008; (c) Ian Howat

Revision history:

05-Dec-2017 18:43 harro Added
05-Dec-2017 18:47 harro Updated [Narrative]
05-Dec-2017 19:53 harro Updated [Narrative]

Corrections or additions? ... Edit this accident description