What happened
On 18 November 2006, an Embraer 135, registration ZS-OTN, was operating a scheduled international service from O.R. Tambo International Airport in Johannesburg, South Africa, to Ndola International Airport in Zambia. While cruising at 37,000 feet above mean sea level, approximately 50 nautical miles northwest of Bulaway/way, Zimbabwe, the aircraft's number two engine experienced an in-flight shutdown.
The flight crew reported a sequence of cockpit indications including a loss of power on the number two engine, a drop in the Intermediate Turbine Temperature (ITT), and a momentary surge back to normal power before the engine failed completely. During the event, the crew observed the engine oil quantity plummet from 12 quarts to 5 quarts. Attempts to perform an in-flight relight were unsuccessful because the crew could not obtain any N2 power turbine speed indications. After declaring a Pan-Pan call to Harare Control, the crew diverted to J.M. Nkomo International Airport in Bulawayo. The crew successfully secured the inoperative engine according to emergency procedures and performed a single-engine landing on Runway 13. There were 0 fatalities and 0 injuries among the 26 people on board.
The investigation
Following the diversion, the aircraft underwent maintenance inspections. Investigators focused on the failed engine, which revealed that the input gear-shaft of the accessory gearbox had failed. The accessory gearbox was subsequently removed for deeper analysis. Records indicated that the aircraft's last phase inspection had been completed on 24 October 2006, with 136.3 flight hours accumulated since that service.
Findings
- The primary cause of the engine shutdown was the fracture of the accessory gearbox input-shaft bevel gear due to fatigue.
- This mechanical failure led to the total shutdown of all components driven by the accessory gearbox, including the fuel pump.
- The loss of fuel supply resulted in the engine flameout.