Royal Maroc B738 near Lisbon on Sep 9th 2017, engine shut down in flight

Last Update: August 24, 2020 / 14:55:38 GMT/Zulu time

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Photo of Royal Air Maroc CN-RNW, Boeing 737-800 — Royal Air Maroc CN-RNW, Boeing 737-800 (Photo credit: markyharky / Flickr / License: CC by)

Incident Facts

Date of incident
Sep 9, 2017

Classification
Incident

Cause
Engine shut down in flight

Airline
Royal Air Maroc

Flight number
AT-981

Departure
Lisbon, Portugal

Destination
Casablanca, Morocco

Aircraft Registration
CN-RNW

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Royal Air Maroc Boeing 737-800, registration CN-RNW performing flight AT-981 from Lisbon (Portugal) to Casablanca (Morocco), was climbing out of Lisbon when the crew shut the #1 engine (CFM56, left hand) down. The crew stopped the climb at FL180 and decided to continue the flight to Casablanca, about 290nm south of their present position, and landed safely in Casablanca about 50 minutes later.

The occurrence aircraft remained on the ground in Casabanca for about 23 hours before returning to service.

A listener on frequency reported the crew declared PAN PAN PAN reporting they had shut the #1 engine due to an engine oil problem. The crew decided to continue to Casablanca.

On Sep 28th 2017 Morocco's AIB reported the occurrence was rated a serious incident and is being investigated by Morocco's AIB. The AIB reported the engine was shut down during the climb, the aircraft sustained minor damage.

On Aug 24th 2020 Morocco's BEA released their final report in French only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a French only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).

The report concludes the probable causes of the incident were:

The clogging of engine #1 oil filter, which prompted the crew to shut the engine down, was most likely the result of excessive presence of silicone in the engine oil filter.

This silicone which polluted the engine oil, would probably originate:

- an infiltration of material from outside through the oil filter (e.g. sand)

- internal degradation of the oil filter constituent

- degradation of one of the components used for lubrication

The BEA reported the aircraft was climbing through FL140 when the crew received an "OIL FILTER BYPASS" message for the left hand engine. The crew reduced the engine to idle thrust, the oil filter message prevailed however prompting the crew to shut the engine down. The crew continued the climb to FL180 and continued to destination for a safe landing.

The BEA analysed that the crew maintained the principles of CRM throughout the flight. The FDR and CVR showed the crew applied the relevant procedures in accordance with the manuals. The instruction of the manual to land at the nearest suitable airport, which was Tangier which was above Minima and suitable for landing, was probably not adhered to based on technical-logistics reasons to the extent that the maintenance facilities of the operator were located at the destination.

Maintenance records of the engine oil did not reveal any discrepancies in terms of maintenance.

The manufacturer analysed the bypass oil filter alert was very real and produced by clogging of the engine oil filter with excessive silicone.