PW120/PW150 engines

[ALLMCC]

Can any of you experts out there advise if there is a specific procedure for cutting power on these engines - have noticed on several such powered aircraft that, after parking on stand, power seems to reduce to a fast idle for around 60 secs before engine power off. Have seen this on ATP, Q200/300/400, ATR42/72.

Also, have noticed what appears to be an engine brake but have only witnessed this on ATR42/72. You can tell I'm no technical wiz - just interested to know!

[False Capture]

The engines are controled by 2 seperate levers - the Power Levers and the Condition Levers. The power levers control the thrust of the power plant from Max rated Torque to max reverse, this is indicated on the engine torque gauge as a percentage of Max Torque. The condition levers control the propeller speed, feathering and the HP fuel shut-off valve, this propeller speed is indicated on a seperate gauge as a percentage of max propeller RPM - known as NP. Once the aircraft is on stand the Power Levers will be on the rear stop in the Ground Idle position. The Condition Levers are then brought rearwards into the feather position range - this is what you called "fast idle" when really it's refered to as "feathered". The period of time required in feather is generally 30 secs. The reason for doing this is to allow the oil from the propeller hub to return to the oil tank in the Reduction Gear Box, when the engineers carry-out an inspection they then get an accurate indication of the oil quantity. If feathering is not done then there is a tendency for the engineers to top-up the oil quantity to the perceived level and in the process over-fill the tank which can lead to the failure of the seals around the propeller. Once the propeller has been feathered the engine is then shut-down by moving the Condition Lever through a baulk/gate to the Fuel Shut-Off position which closes the High Pressure valve/cock and thereby removes the supply of fuel to the engine.

The PW120 series engines are free-spooling turbo-props ie. there is no direct mechanical linkage from the powerplant to the propeller. As a result it's possible to have the engine running whilst the propeller is stationary. This is the approach ATR took when designing the ATR 42 as it reduces weight and costs by removing the requirement to have an APU. With the engine running and the propeller brake applied to the propeller (usually only fitted to no. 2) the engine is able to meet the aircraft's air-conditioning and electrical demands - ATR refer to this operation as Hotel Mode. Unfortunately, when the a/c is in Hotel Mode many ground-crew wont work on it due to the noise, the efflux from the engine and for fear of the propeller brake being accidently released by it's pilots - it's also prone to an over-temperature warning if there's a tailwind which requires engine shutdown . Essentially you're right there is a brake but it's applied to the propeller not the engine

[ALLMCC]

False Capture

Many thanks for your detailed explanation!