Re: ATR Prop Brake ???

From:         commutrdog@aol.com (Commutrdog)
Organization: America Online, Inc. (1-800-827-6364)
Date:         14 Aug 95 03:43:26 
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James...

I fly the ATR and it is the only turboprop in production (as far as I
know) which has a prop brake.  This device is used in lieu of an auxiliary
power unit, which is a small turbine engine used on many aircraft for air
conditioning and electrical power while on the ground.

The Pratt & Whitney engines on the ATR are of the "free turbine" type.
This means that the power turbine is not directly connected to the
propeller, therefore the propeller can be stopped and the engine can still
run.

The design of the ATR is such that for passenger boarding, either an
external power source must be available or an engine must be running.  If
neither condition is met, there is no cabin ventilation and minimum cabin
lighting.  There is much debate on the logic of this arrangement.

Aircraft such as the Jetstream cannot have a prop brake because the design
of their engines is different.  There is a direct link between the engine
and propeller.

This was a very good question.  You are quite observant.

Nick R.