I imply that DB is saying that the instructor is training to slip for an engine fire in a 172. While not no, I can't find that procedure in any of the six 172 flight manuals I have reviewed with this question in mind. What I do find, is that from as far back as the 172N, Cessna does
state that for a wing fire, to slip to keep the flames away from the fuel tank and cabin. Now, aside from fuel, I can't imagine what in a 172 wing is going to burn enough to notice, but okay, Cessna wrote a procedure, so that's what you do.
But let's dissect Cessna's procedures here: For an engine fire, shut down, and isolate the fuel. For a wing fire, side slip, but there's no mention of shutting the engine down! So it sounds like the instructor is mixing together two different procedures! Perhaps (and I'm speculating) Cessna thinks it's too much to expect a pilot of a 172 to perform a viscous slip with an engine on fire while gliding, so they want the pilot to focus on a good gliding forced landing. And, they're content for you to slip with a running engine for a wing fire. As well as being experts on their planes, Cessna are also experts at evaluating "average" pilot skills, and avoiding presenting needlessly complex or task saturating procedures. They will write what needs to be written, though will very certainly avoid writing more than is needed.
So, when the instructor presents a procedure for slipping for an engine fire, pull out the flight manual, and have a read (again, 'cause you've already read it a few times, right?
) . Look up engine fires - no procedure stating a slip, but look.... a page later, slip for a wing fire! You instructor is required to instruct you in
accordance with the flight manual procedures, not to mix and match them....
What we
don't want is your faltering recollection during a stressful situation, to have you remembering to shut down the engine, and slip away from the flames when you have a fire, because if it were to be a
wing fire, Cessna says you can leave the engine running, so why shut it down?