Ours is a bit easier to scan for. It's on the center panel a little bit above and to the right of the ROLL DISC handle:
http://www.airliners.net/photo/Air-Nostrum-(Iberia/De-Havilland-Canada/0628640/L/&sid=dda50b7bcd928c292eabebda543f7d35
I hate your engine instrument stack, I just want to say that, but at least they're where both pilots can see them. Long treatise about why our props can kill us follows.
The prop governor on the Brasilia is like any other prop governor for the most part: it uses oil pressures working in opposition to get to equilibrium. High pressure oil is provided from the prop RGB pump to the governor. Supply oil drives the prop towards feather, and metered oil (prop governor output) moves the prop towards fine pitch. Moving the condition lever to FEATHER will dump metered oil pressure and allow supply oil to drive the prop towards feather. (It does engine control related things too, but that's not important right now.) The electric feathering system, activated by the ELEC FEATHER switch on the overhead, the autofeather system, or the engine fire T-handle, opens the feathering solenoid valve and activates the electric feather pump, which provides oil pressure that's even higher than supply oil pressure to drive the prop towards feather.
Here's the PCU (right) and prop servomechanism (left) on the 14RF9-EMB120-PW118 combination:
(from the NTSB report into Acey's prop control accident)
Rube Goldberg himself could not have come up with a better design, but basically, the prop governor turns the transfer tube, which turns the pitch change screw in the prop dome, which moves the pitch selector valve, which allows oil to flow to one side or the other of the piston in the prop dome that actually moves the propeller blades. Note that oil pressure is required to drive the blades in either direction. In flight, with the propeller subject to air loads and especially at high airspeeds, the natural tendency is for the prop blades to go to fine pitch (which is backwards from what most multiengine airplanes have). In this respect, the prop is fail-deadly. There are a few ways you can kill yourself/get killed with this combination.
One is a loss of oil pressure. The propeller will start to move towards full fine pitch, then pitchlock—that is, it will freeze where it is. Pitchlock actuation is indicated to the pilots by an increase in Np, but then it'll stop about 2 to 4% higher than where it was set. The prop is basically fixed-pitch at this point and will behave as such (more airspeed = higher Np and so on). Hopefully, if you hit the electric feather switch, there'll be enough oil pressure to feather the prop. If the engine has really quit, putting the CL to FEATHER won't do anything, and you'll have to reach up and hit the ELEC FEATHER switch on the overhead to get the prop to feather. (Remember, oil pressure is REQUIRED to move the prop.) Pitchlock prevents (or helps prevent...) overspeed in the event of a loss of oil pressure, but it won't result in any decrease in prop drag if the engine has quit.
Another is moving the power lever below flight idle in flight. This disables ALL of the prop control safety features and you'll rapidly get a propeller overspeed. The bad news is that above a certain Np (~120%), the electric feathering system does not have sufficient authority to decrease the prop's pitch. So, yeah. Don't do that. Ever. We have a solenoid in each engine nacelle that should mechanically prevent the selection of a power lever angle below flight idle in flight.
The failure mode, though, that was discovered on one of the ASA accidents, is a little more involved. The Rube Goldberg contraption in the PCU that engages and turns the transfer tube has failed before - and you wind up with a prop you can't control. In the case of ASA, the PCU would be asking for feather (indeed, the accident aircraft's left PCU was found in the 79.2-degree feather position), but the prop would happily go to full fine pitch and stay there. There's not a thing you can do about it. When the system was originally certificated, the probability of that failure was determined to be extremely remote (10e-6) and so no redundancy was required. The probability of that failure remained extremely remote until Hamilton Sunstrand changed the manufacturing process and titanium nitrided the splines (I guess it was cheaper). The harder material resulted in PCU wear so great that, in post-accident inspection of certain EMB 120 aircraft, the mechanics could not
re-engage the transfer tube.
(That's one of those Code Brown/cold sweat moments, if you ask me.)
Incidentally, this failure mode can be caught by a before takeoff manual feather-unfeather check ("Observe consistent Np anytime a propeller is feathered, by whichever means..."). And in fact, it has been caught by that manual feather-unfeather check.
The net result is that titanium nitrided splines are no longer used and we baby the crap out of the props on the Brasilia.
(threadjack over, but I like talking about this stuff, so I'll subject you all to it!)
