When an airline needs to transport a spare engine to a 747 far away, it turns out the most efficient way to get the job done is to install a fifth engine on a healthy 747 and carry it there under the wing. It doesn’t happen often, but Qantas recently completed the feat, flying from Sydney to Johannesburg with an extra Rolls Royce engine weighing 6.6 tons. Pilots need special training to learn to fly straight and level with the extra weight and drag from the engine, the airline said.
Source: avwebA Rare Five-Engine Flight For Qantas