What caused the VSI and ALT bouce in the IMC?

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?


Only if engaging the alternate cuts off the primary. Because in that case,
when you engage the alternate air, you now have the situation you tested
(alternate air ONLY). If, OTOH, the perversities in the design are that the
primary air is left connected, then you do not have a valid test. Consider the
following scenario: You've done the test, and find that there is a 75 foot
difference with alternate air.

Then one day you are flying in the soup, you see a saucer shaped apparition,
you are boarded by little green men who take the cowling off, reroute the
engine exhaust into the static port plumbing, phone home, and vanish. Before
looking for Area 54 in the AF/D, you notice the altimeter shows you
underground.

Ok, pull the alternate air. Now you're still underground, but with a 75 foot
difference. You're still hosed because the hosed primary air is still part of
the system.

So, the alternate air had better cut off the primary air!

If it does (as it should) then the test is valid and useful.

Jose


--
(for Email, make the obvious changes in my address)

"Teacherjh" wrote in message
...

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?


Only if engaging the alternate cuts off the primary....
(snip LGM scenario)

So, the alternate air had better cut off the primary air!

If it does (as it should) then the test is valid and useful.

Does it, in your spam can? In mine? I probably have to go home and study the
systems, but I admit I can't remember this detail in the POH. Or is there
maybe some regulation behind your use of "should"? Inquiring minds want to
know.

-- David Brooks

I know mine does not. It just opens the static line to the cockpit.

David Brooks wrote:



Does it, in your spam can? In mine? I probably have to go home and study the
systems, but I admit I can't remember this detail in the POH. Or is there
maybe some regulation behind your use of "should"? Inquiring minds want to
know.

-- David Brooks

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

Does it [cut off the primary], in your spam can?

Dunno. Have to check. But it had better if it's to be of use.


Or is there
maybe some regulation behind your use of "should"?


No. I am not from the FAA, nor do I play one on TV.

Jose

--
(for Email, make the obvious changes in my address)