Early last month, on July 8th, a Comair Boeing 737-800 was forced to make a diversion and emergency landing when an engine shut down in mid-flight. The aircraft, registration ZS-ZWE, was performing flight MN-494 from Cape Town to Lanseria (South Africa) and had 182 passengers and six crew.
The incident began as the flight was about to reach the top of its descent into Lanseria. At that point, the crew noticed a left engine (CFM56) low oil quantity indication. The oil quantity reading was at 17%.
At this point, the decision was made to notify dispatch, who instructed the flight crew to monitor the oil quantity. Continuing their decent towards Lanseria, the crew saw the oil quantity reduced to 0% forcing the crew to shut the engine down. As a result, aircraft was diverted to Johannesburg. The flight landed safely on runway 21L.
A post-flight inspection revealed that there was engine oil on the inside of the engine cowlings. Furthermore, the starter drain/fill magnetic plug housing was found loose inside the engine cowlings.
The South African Civil Aviation Authority (SACAA) rated the occurrence and incident, opening an investigation and releasing a preliminary report. The findings of the investigation showed that the aircraft suffered a starter failure of the left engine the previous day while preparing for departure from George (South Africa).
The only Licensed Aircraft Maintenance Engineer (LAME) who was available to perform the repairs at George was permanently located in Capetown but was in George on relief duty for the local LAME. The individual called into Johannesburg in an attempt to locate a replacement starter unit. A starter unit was eventually located, found on a serviceable engine which was currently in the workshop at Johannesburg. The starter was dismounted and then shipped to George, arriving about four hours after the starter failure.
While waiting for the replacement parts to arrive, the LAME attended to other aircraft. Upon receiving the replacement starter, the LAME began to dismount the defective starter but noticed that the part number of the dismantled starter and the replacement were different. After consulting with maintenance in Johannesburg it was confirmed that the parts were interchangeable.
Finally, after six hours after the initial starter failure, replacement work was complete and aircraft ZS-ZWE was released for ongoing flights. In wasn’t until the next day, during the incident above, that first indications of oil quantity reduction occurred.
The SACAA stated that the Aircraft Maintenance Manual (AMM) had requirements regarding the starter drain/fill magnetic plug torquing. Subsequently, a safety wire should be attached. However, the relevant computer software system showing the applicable AMM was not available to the LAME, according to the Aviation Herald. As a result, the LAME did not torque the magnetic plug at the required torque. Furthermore, the safety wire was not applied.
In its findings, the SACAA wrote:
“The engine oil leak was due to a magnetic plug that loosened during operation as it was not torqued and secured with a safety locking wire as per the applicable AMM procedures.”
We reached out to Comair for comment but have yet to hear back at the time of publishing this article.
Comair is a South African airline that operates Boeing 737 aircraft under the branding and livery of British Airways. According to Wikipedia, as of July 2019, the airline has a fleet of 18 Boeing 737 aircraft. This includes a single 737 MAX (with 7 more on order).