What happened
On 8 July 2019, a Boeing 737-800NG operating a commercial flight from Cape Town International Aerodrome to Lanseria International Aerodrome experienced a significant loss of oil in its number 1 engine. While cruising approximately 30 nautical miles south of Potchefostroom, the flight crew noticed the oil quantity indicator had dropped to 17%. Following guidance from the Maintenance Control Centre, the crew monitored the levels, continuing the flight until the oil quantity reached 0%. At that point, the crew performed an in-flight shutdown of the number 1 engine and requested a diversion to O.R. Tambo International Aerodrome. The aircraft landed safely at the destination, where emergency services met the aircraft on the apron. There were no injuries to the 194 passengers or the 4 crew members on board.
The investigation
The investigation into the incident focused on the maintenance performed on the aircraft the previous day. On 7 July 2019, the aircraft ZS-ZWE had undergone a replacement of the engine number 1 starter at George Aerodrome after a failure during start-up. The investigation established that the maintenance engineer performing the task was managing multiple aircraft turnarounds and was unable to access the official Aircraft Maintenance Manual (AMM) at the time of the repair. Instead, the engineer relied on verbal instructions provided by a base station in Cape Town. Post-incident inspections of the engine bay revealed that the starter oil drain/fill magnetic plug had become detached and was found resting on the bottom cowling.
Findings
- The primary cause of the oil leak was the separation of the starter oil drain/fill magnetic plug from its port.
- The magnetic plug was not properly secured or wire-locked following the maintenance performed on 7 July 2019.
- The maintenance engineer was working under high pressure, managing several simultaneous aircraft requirements.
- The engineer's reliance on remote verbal instructions rather than the official maintenance manual contributed to the omission of the locking procedure.
Safety action
- It is recommended that civil aviation authorities require maintenance organizations to maintain offline systems or hard copies of electronic manuals to ensure personnel can access official procedures when digital systems are unavailable.