Incident Overview
On September 9, 2017, Royal Air Maroc Flight AT981, operating a Boeing 737-800 with registration CN-RNW, departed Lisbon (LIS) at 16:39 UTC bound for Casablanca Mohammed V (CMN). During the climb phase, specifically upon reaching flight level FL140, the crew received an 'Oil Filter Bypass' warning light for Engine 1. At the time of the alert, all other engine parameters remained within normal limits.
Crew Actions and Outcome
In response to the warning, the pilot in command initiated the appropriate emergency procedures by reducing the power lever to the 'Safe Power' setting to verify the fault. Despite adjustments to thrust settings, the 'Oil Filter Bypass' indication persisted. To prevent potential engine damage, the crew voluntarily shut down Engine 1. The aircraft continued its flight on a single engine at FL180 and landed safely at Casablanca Mohammed V Airport at 17:38:54 UTC. There were no fatalities or injuries among the 2 crew members and 89 passengers on board.
Investigation Findings
The Moroccan Bureau of Aviation Accident Investigations (BEA) classified this event as an incident warranting a technical investigation. The inquiry relied on flight data recorder (FDR) and cockpit voice recorder (CVR) data, crew interviews, and physical tests conducted on the oil pump, engine oil filters, and the harness responsible for transmitting the alert signal. The aircraft had accumulated 39,409 total time in service and 16,744 cycles prior to the event.