Originally Posted by rickair7777

If you're taking the longer view...

Environmental concerns may well drive rapid transitions to newer, more efficient equipment types and that may have to happen inside the normal life cycle of aircraft depreciation. So somewhat older planes (vs. newer of the same type) might be better if you have to unload them earlier than anticipated.

If I were an airline manager, I'd be trying to guess when the new technology on the horizon will inject step-change fuel efficiency (and thus carbon efficiency) into the market and time my fleet planning accordingly.