Originally Posted by
aerobat77
the pt6a definitly does not has any pitch locks, you see it nicely on a normal shutdown- you can leave prop lever full foward and the propeller with nevertheless fully feather when the engine spools down .
In terms of always feathering on shutdown, this is not always the case. For ease of explanation, I will quote an earlier thread on this subject...
"many turbine floatplanes fitted with PT6 engines are fitted with blade latches to allow the propeller to remain in a zero thrust position at zero airspeed after the engine is shutdown in preparation for the next start. To engage the blade latches you have to shut the engine down in beta or reverse - if you miss the latches the blades will feather.
The reason why blade latches are fitted is to increase control options on start. When we're on the water we don't have brakes - if we're starting up in a tight location the forward speed generated whilst we wait for the blades to come out of feather onto the fine stop can make life very difficult. It is only when the blades reach the fine stop you have a beta or reverse option available, and by this time in a C208 we're traveling at about 3 to 4 knots.
When we start with the pitch locks engaged a touch of reverse after startup is required to disengage the latches and give us instant control over the propeller - forward, zero thrust and reverse. The biggest drawback with shutting down on the pitch locks is it takes ages for the propeller to slow down enough to get past the propeller - it is very disconcerting attaching a mooring line to the bow cleats with your head only feet away from a propeller that is still spinning at high speed with no engine noise. Additionally, if you're facing directly into a significant breeze with the blades latched in zero thrust they will not stop spinning at all in zero pitch - and with the gas generator shutdown there is no oil pressure available to lubricate the reduction gearbox. Stopping them requires the use of lots of care and a towell for padding.
There are two advantages with shutting down in feather in the C208. The first is the propeller stops quicker. The second is the scavenge pumps return the oil from the reduction gearbox to the accessory case to allow the oil level to be accurately determined. There is a slight difference in resistance to gas flow depending on whether the blades are feathered or not - the ITT at feather is very slightly lower than when the blades are in fine pitch."