After talking with Ron about his accident I asked him to post a message
about how the AOA gets information as I didn't have access to the mail list
at that time.  I thought a review should be addressed to the mail list
regarding AOA and when it can be used as a backup to faulty IAS and
pitot/static systems.

The PSS AOA system uses both wing loading and pitot static pressures to
gauge AOA.  The wing loading is determined by measuring the differential
pressure between the lower and upper wing static.  A pitot/static pressure
is used by the AOA to get dynamic pressure and is usually gotten from the
existing system although some folks install a separate pitot/static system
dedicated to the AOA.

AOA is derived by dividing the wing loading by the dynamic pressure.

Should the IAS indicator fail, certainly the AOA would make an excellent
source.  However, if the pitot/static system fails (covered pitot tube for
example) then the dynamic pressure is in error and the IAS indicator and
the AOA will both give invalid indications;  garbage in garbage out.

Ron reported that the pitot tube was covered by tape or clogged by
mud-daubers  This  results in the dynamic system pressures being falsely
low in relation to the speed.  This system error would have resulted in a
low airspeed indication and a high AOA indication.

I hope this helps.

Jim
Proprietary Software Systems, Inc.
www.angle-of-attack.com
(952) 474-4154

Jim
Proprietary Software Systems, Inc.
www.angle-of-attack.com
(952) 474-4154