Ray Andraka wrote:

Also the FAA materials for the IFR written mention several
times that breaking the VSI glass is the way to get alternate static on an
airplane that doesn't have a valve. I wouldn't think they'd make such a big
deal about it if an alternate static source was requried for IFR cert.


It should be mentioned here that this trick only works on an
unpressurized a/c. You won't get much activity on the VSI needle
if you try this with a pressurized aircraft!.

--

-Gord.