Just curious, but what exactly is the point of the ALT SEL button? The fact that they've put it in there suggests that there would be situations where you wouldn't want the AP to stop the climb or descent at the selected level, so can anybody tell me what those situations might be? It seems like the only reason to make you manually arm the level-off is to catch pilots out.

 

Discuss

I read somewhere when the real Q300 version of the plane was built, having to arm the altitude via ALT SEL was a bug, and when they built the real Q400 version of the plane, they made it the same (didn't fix the bug) so pilots would not get confused when swapping between planes.Can't find where I read this, though. Might have been one of the tutorials or FAQ's at Majestic.

 

Edit - Found it in the detailed tutorial

 

WARNING! The FD will not capture an altitude unless it is preselected on the AFCS with an ALT SEL displayed on the PFD. This is a peculiarity of the aircraft- ALT SEL does not come on automatically. It is a Bombardier design flaw that was never fixed (I heard that it was because it kept operational commonality with the -300 and -200 models).

Apparently the Q400 was intended to have lots more goodies (auto throttle, no ALT SEL, no power levers but instead switch control for the prop settings) but it all fell by the wayside for the sake of commonality with the previous models.

 

The trick with ALT SEL is to press it BEFORE making the VS/IAS selection. Easier said than done...

Man, at this point,(part 7), I'm even saying it in my head in the car!

RNAV Approaches with the go around altitude set already with the aircraft in VNAV?

... That's about the only place I can see it being anything other than an "oops, we just busted cleared level" button