What are the consequences of attaching an unused extra engine under Boeing 747 wing? It turns out Boeing 747 can carry an extra engine under its left wing in case there's need to transport an engine somewhere far away. The engine is attached between the body and the left inner engine and isn't operational during such flight.

What implications does that have on the airplane operation? I guess drag is increased notably and also drag increases only for left wing and so the plane should tend to well, turn left in case engine thrust is equal on both sides of the plane so now engines under right wing have to produce more thrust or something like that. Also the engine weighs quite a lot so less cargo may be put into the plane. Also fuel consumption increases and flight range decreases accordingly.

Is that all? What are the consequences of attaching an extra engine under Boeing 747 wing?
Operationally you would be more restricted in terms of trimming. Back when we had manual loadsheets there would be a demarcated area '5th pod operations limit'. Only the gods of the loadsheet deptartment would be allowed to do the loadsheet for these flights. I think Qantas would put a loadsheet man on board for these flights but I could be mistaken.

The flight would be re-timed as the usual 90 minute turnaround time would not be sufficient. I believe 2 hours on top of the regular turn was the norm.

An additional fuel stop was usually required as the fuel-burn was atrocious with that big thing hanging off. The weight penalty was compensated by reducing cargo.

I was working in Singapore in the 80s and we usually had Qantas doing this a few times a year. The engines were ex-SIN .. I don't know if they were overhauled in SIN or if they came into SIN on another freighter. At the time there were not many B747 freighters operating into Australia. I believe Flying Tigers had one but that was from US to Australia to SIN.. It did not do SIN-Australia.