Northwest, and Delta, were actually the launch customers for the PW
powered 757's in the mid 80's. I believe that the PW2000 series engine is more fuel efficient that the RB211, but I could be wrong.
They cannot just decide to put PW
engines on an A/C that has been rigged for RR
. The PW
engines use what is called a FADEC, full authority didgital engine control, to control the fuel metering and other engine operations. There is no physical connection between the thrust levers in the cockpit and the engine only a wire bundle. The RR
engines use a regular hydromechanical fuel control, but they added a computer, an EEC or electronic engine control, that does the final fuel metering. Since the RR
has an old fashion fuel control as part of its fuel metering system there is a cable and pulley system from the thrust levers to the engine.
differences between PW
powered 757s and RR
powered 757s are more than skin deep.