Which popular turboprop engine feathers its propeller blades with each shutdown?

Question

Chapter 12 of the FAA Airplane Flying Handbook, discussing multiengine flying, goes into quite a bit of detail in the propeller section about how most feathering-propeller-equipped engines on multiengine aircraft have a mechanism that prevents the propeller from feathering if the engine RPM is below a certain value, before mentioning that one particular widely-used turboprop model does not have this mechanism:

As just described, a loss of oil pressure from the propeller governor allows the counterweights, spring, and/or dome charge to drive the blades to feather. Logically then, the propeller blades should feather every time an engine is shut down as oil pressure falls to zero. Yet, this does not occur. Preventing this is a small pin in the pitch changing mechanism of the propeller hub that does not allow the propeller blades to feather once rpm drops below approximately 800. The pin senses a lack of centrifugal force from propeller rotation and falls into place, preventing the blades from feathering. Therefore, if a propeller is to be feathered, it must be done before engine rpm decays below approximately 800. On one popular model of turboprop engine, the propeller blades do, in fact, feather with each shutdown. This propeller is not equipped with such centrifugally-operated pins due to a unique engine design. [FAA Airplane Flying Handbook (FAA-H-8083-3B), Chapter 12 ("Transition to Multiengine Airplanes"), my emphasis.]

What is the identity of this standout, and what unique aspect of its design is the reason for this difference from other feathering-propeller-driving engines?

Answer 1

This is typical for the De Havilland Canada Dash-8, which is powered by Pratt & Whitney Canada PW100 engines. Other aircraft powered by that engine also seem to have their propellers feathered during shutdown. The propellers are only unfeathered after the engine has started (see e.g. this YouTube video of an ATR 72-600 starting its engines with the propeller still feathered).

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From the Dash-8 Q400 manual:

Manual Feathering

Propeller manual feathering is used during engine shutdown by selecting the appropriate condition lever to the START & FEATHER and/or FUEL OFF.

^{(Dash-8 Q400 Manual - Propeller)}

Normal shutdown procedure is to select the CL (condition levers) to START & FEATHER first, then let the engine run for about 30 seconds (with the propeller already feathered) and then select FUEL OFF:

POWER AND CONDITION LEVERS ..... DISC / START&FEATHER
[...]
COND. LEVERS (AFTER 30s) ..... FUEL OFF

^{(Dash-8 Q400 - Normal Procedures)}

^{(Dash-8 Q400 Manual - Powerplant)}

The manual does not state a reason for feathering the propeller on every shutdown. It does quickly reduce the propeller speed on shutdown and therefore allows the ground crew to approach the aircraft without much delay. Such a design is only possible on free turbine engines because otherwise high drag from the feathered propeller would require too much power during starting¹.

The difference to other turboprops might be related to the design of the alternate feathering system:

Propeller Feather Pump

The Auxiliary Propeller Feathering Pump Unit provides an independent means of feathering the propeller in the event of a failure of the primary means of feather. The auxiliary pump consists of a 28VDC electrical motor driving an external gear pump which supplies a secondary source of pressurized oil for feathering the propeller. The feather pump is also used for feathering and unfeathers the propeller as required for maintenance purposes.

^{(Dash-8 Q400 Manual - Propeller)}

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¹: For example, on the Dornier 228 (powered by single spool Honeywell TPE331 turboprop engines), the propellers are intentionally unfeathered for starting to reduce drag:

For ground starting, the propellers are held mechanically for minimum drag in a fine pitch position by spring actuated start locks. [...] To engange them when the engine is not running the UNF-PUMP must be activated with the POWER lever in REVERSE until the minimum propeller blade angle is reached.

^{(Dornier 288-100 POH - Airplane & System Descriptions - Propellers)}