Commonality

[West Coast]

Asked of me and I couldn't answer..........

During acquisitions, the buyer will often dump planes that have different engines to maintain fleet commonality. As an example an operator may dump PW powered aircraft even though they operate the same type but with different engines.
Is it that cost prohibitive to re-engine the undesired aircraft with new engines? Has it been done on a large scale that anyone is aware of?
What of differing avionics packages, can they be made common without breaking the bank?

[411A]

Easier said than done.
If you change engines, the pylon needs to be changed as well, as each is designed with a specific engine in mind.

The only 'really easy' (more or less) engine change was on older straight pipe powered 707-300's (JT4A engines) that were re-engined with JT3D fans.
Engine/pylon change, rudder Q feel etc, and not all that much else.
This produced an aircraft that was an exact copy of an already certificated aircraft.

On a newer type, the cost may well be prohibitive, not so much the engines as the pylons, engineering etc.