Questions for Metro Pilots
 

Hey guys,

I have a few questions for anyone who currently flies a metro. I've received different and conflicting answers from fellow pilots, and I was hoping for added input.

1. In my groundschool manual (electrical systems chapter, DC voltmeter switch), it states..... "to read the output of the selected generator or battery, the corresponding battery or generator must be in the OFF position. If left ON, the voltmeter will read DC Bus voltage." I don't quite understand this. Does this mean that if I want to read the voltage of the left generator in flight, I would actually have to turn the left gen OFF?

2. Do you know what the 3 CBs in the wheel well are for? I believe one is the CB for the Generator output sense relay, the 2nd is the CB for the ground fault sensing relay, and the 3rd is the CB for the Gen relay. There is also a 4th CB on the opposite side, which I believe is the CB for the voltmeter. I'm not too sure though.

3. I do not understand the purpose of the "Reset" position for the battery and generator switches. The manual explains it acts to "prime" the generator. I dont see how this works.

4. There are 4 static ports on the nose. I know they are all for the pressurization system, but what exactly is each one for? I know 1 is for the 7.25 PSI relief valve for dump valve,.

5. If the trim system fails, you apparently will get a heavy nose up pitch. Why is this?

If anyone can shed some light on any of these questions, I'd greatly appreciate it. Thanks a lot.

I'll give it a shot.
 

Hey Mac. I've got a little free time so I'll see what I can do.
This gave me a hard time too when I first check out in the Metro. The idea here is that "Bus Voltage" is really an average of the voltage output from the two gens and the batt. In order to read the volts of one gen in particular you need to disconnect that gen from the bus. You do that by selecting 'off'. The gen is still producing volts (as selected and read from the volt meter) but since it's not connected to the bus it's not part of the "bus voltage."
I can't find a definite answer to this question and I simply don't remember. Your best bet is to ask one of your mechanics
The Gen is protected by the GCU--Gen Control Unit (it senses overvoltage, reverse current, shorts, and regulates gen voltage). If the GCU detects a fault it'll take the gen off line. If the fault is remedied then you reset the GCU by moving the Gen switch to reset.

The Batt has similiar protection. It's pretty complicated involving two fault transformers that sense a difference in voltage and then removing the ground to the battery, thereby isolating it from the bus. In order to reset the fault relay you need to select reset on the batt switch.
My Metro III manual doesn't have much on this: <<Two upper static ports, on the left and right sides of the cabin, connect to the cabin differential and altitude gauge, and to the pressurization controller. Two lower static ports, on the left and right sides of the cabin, connect to the safety dump valve. A static port on the aft fuselage body, mounted on the left side, is connected to the outflow valve.>> Not sure if that clears it up for you or not.
This doesn't make any sense. If the trim system fails the horiz stab will stay fixed in position. However if the trim system has a short and "runs away" it could go in either an up or down motion. The procedure included selecting the other pilots trim system with the "paddle" but some people that I knew at the time said they would just turn off the gens *and* batt and kill all power to the whole airplane. Yes you would be in a dark cockpit with no one to talk to but you're pretty much guaranteed to stop the trim motion.
But, I'm not aware of any situation where you would have an automatic heavy nose up pitch.
I hope that helps. Congratulations on the new gig.
M.
:cool:

I remember these ports being not just for pressurisation - a couple fed some part of the instrumentation and/or FC?


Perhaps someone more current on the type than I - shouldn't be a hard find - :} .........will come along and blow me out of the water.