A few more thoughts on feathered propellers, if I may.
On a PW120, it is necessary to view the state of the propeller and of the turbomachinery separately, as I already hinted on previously. It is possible to have the propeller feathered or unfeathered independently of the turbomachinery running or not running, although obviously not all combinations are within the realm of the SOPs.
Let us look at the possibilities.
1. Propeller unfeathered, turbomachinery running.
This is obviously the normal operating state in flight. The engine (let me use this word in the sense of "combination of propeller and turbomachinery" from now on) will provide electric power and bleed and most importantly thrust as requested by the power levers; with the power levers in idle, some drag will be expected depending on the propeller RPM. The higher the prop RPM, the higher the expected drag in this case. This substitutes for a speed brake quite well - think shifting down on a manual gear box without pushing the gas pedal on a car.
2. Propeller feathered, turbomachinery running.
This is normal after starting the engine on ground and in flight. The engine will provide only electric power and bleed, no thrust and neither significant drag with the power levers at idle. However, in case of a feather at high power selection expect rather weird indications: torque against a feathered propeller is very high. In case of an unscheduled feather, it is thus required to apply the associated procedure to the engine showing more torque than the other one, which is a bit counter-intuitive at first and requires conscious identification of the issue at hand.
In flight, this state is achievable by either pulling the condition levers back to START/FEATHER or by hitting the alternate feather buttons that are hidden behind a transparent cover on the DH8 and probably similar on the ATR. Both selections require confirmation by the PM.
As the turbomachinery is still running, such a situation is fairly easily rectified, should it be entered by error. Pushing the condition levers forward and/or unselecting autofeather will bring the engine back to normal operating mode (prop unfeathered, turbomachinery running).
3. Propeller feathered, turbomachinery not running.
This is the normal shutdown state of the engine both in flight and on ground. There will be low drag from the failed engine and obviously no power. This condition is covered in performance calculations, trained and keeps the aircraft flyable, preferrably of course with another engine providing power.
Getting the engine to provide power again requires a normal engine start on ground which takes about 45-60 seconds or the application of the engine restart in flight QRH checklist, which takes much longer as it involves resetting various systems and getting the engine into a startable condition first. A bit more than 2 minutes may well be expected.
4. Propeller unfeathered, turbomachinery not running.
This is a rather undesired state. The engine will provide maximum drag and no power at all in flight. It is entered by various common and often-trained malfunctions like a flameout with autofeather not working; there are a few most dedicatedly non-SOP ways of forcing it via the cockpit controls as well. In addition, an intermediate state with a dead turbomachinery and an only partially feathered propeller can be achieved by misapplication of the inflight shutdown procedure: pulling the condition levers back to "fuel off" at once without additionally hitting the autofeather will leave the propeller somewhere halfway between flight range and feather while shutting down the turbomachinery.
This situation is recoverable from. The loose ends can be picked up by applying proper and trained procedures to get the engine back to the state mentioned in (3) rather quickly and possibly later to (1) - which obviously takes more time than may be available in certain flight situations.
I´m rather curious to hear what exactly has happened in the flight deck of the flight discussed here and would be surprised to learn that all SOPs have been followed to the dot...