Imagine that, your plane grounded on airport with an engine fault. New engine is needed. What should an airline do? How to move a spare engine? For Boeing 747 operators, Its easy. Put an extra engine on wing and send!
Here you are Qantas photo released to media.
Qantas Flight 63 took off from Sydney with an extra Rolls Royce turbofan attached to the left wing between an inner engine and the plane's body. The engine was not powered; it just came along for the ride to Johannesburg, South Africa.
The airline said “We're undertaking this rare task to get our customers and our aircraft on their way as soon as possible — rather than shipping this engine across by boat or chartering a freighter aircraft"