"Teacherjh" wrote in message
...

Does engaging the alternate air shut the external static source off? If
not,
it's only a partial test.


Hope so - you use it when the primary air is hosed.

One of us must have cut out too much of the context.

Because you can never know too much about your plane's systems, you engage
the alternate air one day while the static port is working fine and note the
offset. Now you are ready with a known correction, when the time comes that
the primary air is hosed. Is this a valid test?

-- David Brooks