Incident Summary
On 8 July 2019, a Boeing 737-800 aircraft registered as ZS-ZWE, owned by Comair Limited and operated by Kulula, was on a commercial flight (CAW494) from Cape Town International Aerodrome (FACT) to Lanseria International Aerodrome (FALA). The aircraft carried two pilots, four crew members, and 194 passengers (188 adults and six infants). During descent, approximately 10 nautical miles from FALA, the crew observed that the engine 1 oil quantity indication warning caption showed 17%. Following emergency checklist procedures, they contacted area control and requested an early descent from FL330 to FL210. They also contacted the South African Airways Technical (SAAT) Maintenance Control Centre (MCC), which advised them to continue to FALA while monitoring the oil quantity. Should it reach 0%, they were instructed to shut down engine 1 and divert to O.R. Tambo International Aerodrome (FAOR).
Maintenance Background
The previous day, 7 July 2019, the same aircraft experienced a starter failure on engine 1 during start-up at George Aerodrome (FAGG). An aircraft maintenance engineer (AME) replaced the starter, and the aircraft was signed out. The flight from FAGG to FACT was uneventful. The investigation later revealed that during the replacement, the starter oil drain/fill magnetic plug was not locked, a fact that contributed to the subsequent oil loss.
Flight and Diversion
As the oil quantity continued to drop, it reached 0% and the crew shut down engine 1. They requested a diversion to FAOR, which was granted. The aircraft maintained FL110 under radar control and conducted an emergency landing procedure on Runway 21L at FAOR, landing safely. Emergency services escorted the aircraft to the apron. No injuries occurred among occupants, and damage was limited to the starter.
Investigation Findings
The investigation determined that the starter oil drain/fill magnetic plug had separated during the flight from FACT to FALA. The separation occurred because the plug was not locked after the maintenance performed the day before. This allowed engine 1 oil to leak through the starter oil drain/fill port. The incident occurred during daylight meteorological conditions south of Potchefstroom Airport (FAPS), approximately 30 nautical miles from FALA.