Known Icing requirements

[Jeffrey Ross]

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". 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?

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

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.


thanks...

Jeff

[Mike Rapoport]

"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