Tried searching the forum to see if this had been asked before, don't think it has...

Can anyone tell if it is permitted for the A380 to fly with a mix of the Rolls Royce and Engine Alliance types? (and if not, why not?)

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LiSrt:
While I cannot speak directly to A380, the installation characteristics of the engines are VERY different between OEMs:

1) Configuration of the structural interface to the pylon (so Step One: replace the pylon)

2) Instrumentation and control differences (2 vs 3 rotors, temp/pressure limits,... ) (Replace wiring & connectors, new display software...)

3) Complete a flight test program (OEI, etc) and publish documentation...

In short, it's a BIG engineering job, usually tackled only by (e.g.) GE, P&W or R-R Flight Test Center, or Boeing/Airbus flight test operation.

barit1 - thanks, that explains things.