What happened
On 27 February 2013, a Boeing 737-800, registration ZS-ZWP, was preparing for a domestic flight from Cape Town International Airport to OR Tambo International Airport. The aircraft was carrying 181 passengers and 6 crew members.
During the take-off roll on Runway 01, the aircraft reached a speed of approximately 30 kt when a loud bang and significant vibration were felt throughout the cabin. The flight crew immediately observed that the No. 2 engine had lost power, with N1 and N2 gauges dropping to zero. Following standard rejected take-off (RTO) procedures, the crew brought the aircraft to a halt on the runway.
Air traffic control activated the crash alarm, prompting a rapid response from aerodrome rescue and fire fighting personnel. While the aircraft sustained no injuries to its occupants, engine debris was found scattered across a large area of the runway surface, necessitating a temporary closure of the runway for cleaning.
The investigation
SACAA AIID investigators examined the aircraft' and the engine components to determine the source of the failure. The investigation included a review of maintenance logs, flight data recorder (FDR) and cockpit voice recorder (CVR) analysis, and a detailed borescope inspection.
Technical analysis of the engine revealed that several high pressure turbine (HPT) blades had failed. Specifically, three HPT blades were found to have separated below the platform. Further examination of the fracture surfaces indicated that fatigue cracks had initiated on the internal surfaces of the blade cavity. The investigation also noted that the engine oil analysis showed higher levels of aluminum in the rear sump, consistent with the metal debris from the failure.
Findings
- The primary cause of the aborted take-off was the failure of the No. 2 engine due to the failure of an HPT blade.
- A contributing factor was the failure of the HPT blade coating, which led to corrosion and subsequent structural failure of the blades.
- This incident was identified as the fourth such engine failure event involving the specific M10P03 blade shank transition zone cracking pattern in the CFM56-7B engine series.
- The flight crew acted in accordance with established company procedures and maintained effective communication with air traffic control.
Safety action
Following the investigation, the manufacturer, CFM, revised Service Bulletin SB72-0821. The revision reduced the recommended removal interval for the affected population of blades from 25,000 cycles to 16,500 cycles to mitigate the risk of similar fatigue-related failures.