"Jeffrey Ross" wrote in message
...
I'm a little confused as to the requirements that an aircraft must meet to
launch into known icing conditions. To further add to my confusion, the
regulatory requirements (may be just the interpretation of?) has changed
over the years.

My personal situation, I own a '69 Aztec (D model) and 1974 the aircraft
had received an STC for "Flight into known icing conditions". The STC
included the follow:

de-ice boots on the main wings outboard of the engines only
de-ice boots on all the tail feathers
heated anti-ice (?) pads for both props
hot plate (anti-ice) for the windshield

In addition the Pitot tube is heated (static port is on the pitot tube so
its heated too).

The STC specifically says (wording is from memory however) "Approved for
flight into known icing conditions" and then gives the severity of the
icing encounters as "occasional light to moderate".

This is fairly common, very few airplanes are approved for flight into
severe icicng.

It further goes on to list what equipment must be working and installed to
meet the certification, otherwise if anything is not working or installed,
I need to place a plaque saying that flight into know icing conditions is
prohibited.


I guess the questions are,

1) if the testing for the STC was to be done all over again today, would
this aircraft succeed? or is todays certification process for icing so
much tougher that it wouldn't pass?

The test is done be conducting a flight for a certain time into a certain
droplet size icing to simulate stratiform clouds and then again into larger
droplets to simulate cumulus clouds. AFAIK the test has not changed for
many years.

2) What is occasional? less than 1/2 hr in icing conditions? Just long
enough to climb or descend through it?

I think that occasional is defined in weather info (maybe in the AIM) as
being less than half the time but you can look it up.


3) Reading through an article on known icing aircraft requirements
recently published by AOPA (ASF?) it was said that a heated stall warning
switch was also required, I do not have one, and its not listed as a
requirement in the STC.

This may very well be true but should not really concern you since the stall
warning system does not accurately predict a stall on an iced up airplane.
The airplane will stall at a higher speed with ice and different portions of
the wing or tail may stall first depending on the shape and amount of ice.

Mike
MU-2