What happened
On May 11, 2009, at 18:37 UTC, a British Airways Boeing 747-436, registration G-BYGA, was performing a takeoff roll from Tambo International Airport (FAJS) in Johannesburg. During the roll, the No. 3 engine thrust reverser unlock light illuminated while the aircraft was traveling at 124 knots.
As the aircraft accelerated to 163 knots, the No. 2 engine thrust reverser unlock light also illuminated. Immediately prior to rotation, the aircraft's slats retracted. The crew rotated the aircraft and achieved a climb rate of 200 feet per minute. Following these indications, the flight crew performed a fuel dump and executed an air turn back to FAJS, where the aircraft landed safely with no injuries.