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

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

If you own an experimental, what you say is correct.

If you own a certified airplane, you may rest assured that the weight
of the paperwork will exceed the weight of the installed components.
A change to the pitot-static system is considered a major alteration.
If it's a manufacturer's kit or STC, it will be expensive. If there
is no STC or manufacturer's kit, it will be VERY expensive or
downright impossible because it will require a field approval, which
these days usually requires you to hire a DER/DAR.

Just one more way the FAA keeps us all safe from unproven technology.

Michael