What happened
On 10 April 2001, a B747-300, registered as ZS-SAC, was performing a scheduled international flight from Johannesburg International Airport (FAJS) to Heathrow International Airport. During the takeoff roll on Runway 03L, the aircraft reached a speed of approximately 70kt when the crew aborted the departure. This decision followed an audible engine stall and the sight of flames exiting the exhaust of either the number one or number two engine.
Despite the visible flames, engine monitoring systems showed that parameters remained within limits, with the highest recorded Exhaust Gas Temperature being 605°C on the second engine. There were no fatalities and no injuries among the 302 people on board.
The investigation
Following the incident, ground engineers conducted visual and borescope inspections of both engines on the left wing. Initial assessments found no anomalies, and subsequent ground tests at maximum takeoff power appeared successful, leading to the aircraft's release for service. However, a subsequent takeoff attempt resulted in a repeat stall of either the first or second engine without any obvious parameter deviations.
Further investigation by engineers identified that the number one engine had specifically experienced a surge and stall. This engine, which had only accumulated 253 hours since its last overhaul, was subsequently removed and sent to a facility in Japan for detailed repair and inspection.
Findings
- The investigation determined that the excessive wear on the 14th and 15th stage High Pressure Compressor (HPC) outer ducts was the primary cause of the engine surges.
- The wear pattern on these specific compressor ducts led to the instability in engine operation.
- In response to these findings, Pratt & Whitney issued an Internal Engineering Notice (IEN) to guide the inspection of HPC outer cases, duct supports, and diffuser case mounting diameters.