B737 Critical engine?
 

The B737 Flight Crew Training Manual talks about failure of the critical engine. Which of the engines is critical and why???

Well it certainly isn't the APU :}

Sorry about that! Need some more info. At which stage of flight are you talking? If during take-off then the L/H engine would lose the \'A\' hydraulics so the flow for \'gear up\' would dramatically decrease ( only elec pump left) so the landing gear transfer valve would operate to port \'B\' fluid to raise the gear.

It was included as a recite of regulations in a discussion about V1. Haddock you are right it is strange that it was included in the B737 FCTM. Reference to the critical engine was actually removed from the FCTM revision which just came out last month.