Incident
On 29 August 2002 at 0610 Z, a Boeing B747-200 aircraft, registration ZS-SAN, was conducting an international scheduled flight from Johannesburg International Airport (FAJS) to São Paulo, Brazil. The aircraft began its takeoff roll on Runway 03L with 20 crew and 277 passengers on board. Weather conditions were fine with wind from 360 degrees at 5 knots.
Sequence of Events
During the takeoff roll, the crew heard a loud bang, described as an engine stall or surge, emanating from the left-hand side—either from engine number 1 or number 2. The number 1 engine exhaust gas temperature (EGT) peaked at 743°C. The pilot-in-command aborted the takeoff at approximately 100 knots and brought the aircraft to a stop on Runway 03L. Smoke was observed emanating from the main landing gear, prompting the crew to request fire crew inspection. As the aircraft came to a halt, several wheel assemblies on the left-hand wing gear and left body gear began deflating due to overheating brakes. There were no injuries, and the crew and passengers disembarked normally.
Probable Cause
The No. 1 engine stall (compressor stall) was attributed to the following factors: 1) EVBC (engine vane bleed control) off schedule and/or loss of main fuel pump hydraulic pressure; 2) low and high stage compressors mismatch due to one compressor becoming less efficient than the other; 3) excessive compressor blade tip clearance due to wear, causing unstable air at the blade tip area. Additionally, the No. 1 engine 2nd Stage Turbine Rotor Assembly single lug (blade attachment) fractured due to severe thermal stress as a result of internal blockage at the blade root cooling air supply holes, leading to turbine blade leading edge burn-through. The blockage was caused by severe degradation of material that emanated from the 2nd Stage Rotor fiber metal seal situated under the rear retaining plate.