What caused the VSI and ALT bouce in the IMC?

cpu wrote:

1. The plane does not have a alternate static port.

In many countries (including Canada), an alternate static air source is
legally required to fly IFR. In the U.S., it may not be a legal
requirement, but it's still a very bad idea to take up a plane into IMC
without one -- you might not be able to get enough room to swing your arm
hard enough to break the VSI face, and in any case, you might be too busy
trying to control the plane.

I understand that it's a fairly cheap modification (as simple as a little
valve under the front of the panel).

2. I thought smash only VSI will help all the static based instrument
such as ALT, ASI because the static system are all connected. Once
the air bleed through the VSI, it will propergate to the other
instruments through the static connection. I think I am right on
this.

That's correct. Smashing the face of the ALT would also work, but you don't
want to risk breaking that if you're in IMC. The VSI is expendible.


All the best,


David