What happened
On the morning of 8 November 2019, a Cessna 550, registration ZS-CAR, was preparing for a flight calibration mission from Lanseria International Airport (FALA) to Polokwane International Airport (FAPP). During the take-off roll on Runway 07, the flight crew detected a strong smell of oil and observed smoke entering the cockpit, which significantly obscured their forward vision.
In response to the deteriorating conditions, the crew executed an aborted take-off, applying maximum braking to bring the aircraft to a halt. After stopping, the aircraft was taxied back to its hangar and the engines were shut down. Following the shutdown, the aircraft's main tyres deflated; the right tyre deflated first, followed shortly by the left. This was caused by the melting of the temperature fuse plugs. While the crew experienced eye irritation and slight discomfort from smoke inhalation, there were no injuries reported.
The investigation
SACAA AIID investigators examined the aircraft's maintenance history and the sequence of mechanical failures. The investigation established that the smoke and odor were caused by a failure of the number 3 bearing labyrinth seal in the number 1 engine. This failure allowed oil to leak into the high-pressure compressor (HPC), where it mixed with heated, compressed air, creating the smoke observed by the crew.
Investigators also reviewed maintenance records from the previous day, noting that the aircraft had diverted to Lanseria on 7 November 2019 due to similar smoke and oil smells. At that time, maintenance personnel had topped up the engine oil levels but did not identify the underlying seal failure. Further scrutiny of the maintenance logs revealed inconsistencies in how defects were recorded and signed off by the maintenance organization.
Findings
- The primary cause of the smoke in the cockpit was a labyrinth seal failure in the number 1 engine's bearing.
- The operator and the maintenance organization failed to monitor engine oil consumption levels.
- The maintenance engineer misdiagnosed the initial defect, failing to follow the manufacturer's recommended diagnostic practices.
- There was a lack of compliance with standard manufacturer practices and Civil Aviation Regulations regarding maintenance and defect reporting.