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ahinterl

EMER PWR switch questions

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The way the MD-11 EMER PWR switch works looks somehow inconsistent to me.I've attached some numbered screenshots to make the situation clearer. The plane is on ground with external power and air connected. Here the questions:Figure 1 is EMER PWR OFF and the messages as expected. Looks correct to me ;-))Figure 2 shows the situation after moving the EMER PWR switch to ARM: the emer pwr ON light is lit, but there's no battery drain, the symbol has neither load depicted on the synoptic nor is it green. Since ADG isn't deployed, this doesn't look OK to me. There's no message on the SD as well.Figure 3 is after placing the EMER PWR switch to ON, things look okay to me here.Figure 4 is when the EMER PWR switch is moved back one step again to ARM. Though I'd expect the systems to be in the same state as before (figure 2), they aren't: no ON light is lit this time, this looks more correct to me, but now there's the message "BAT CHARGING" on the SD which wasn't there in figure 2 as well.So, there's a difference from which side (OFF or ON) the EMER PWR switch is moved to ARM, the result is different. Besides of the inexplainable ON light lit in figure 2, this doesn't look consistent to me.The question is only whether this is "by design" and a wanted feature or not. I didn't find enough information in the systems manual.Andreas

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The way the MD-11 EMER PWR switch works looks somehow inconsistent to me.I've attached some numbered screenshots to make the situation clearer. The plane is on ground with external power and air connected. Here the questions:Figure 1 is EMER PWR OFF and the messages as expected. Looks correct to me ;-))Figure 2 shows the situation after moving the EMER PWR switch to ARM: the emer pwr ON light is lit, but there's no battery drain, the symbol has neither load depicted on the synoptic nor is it green. Since ADG isn't deployed, this doesn't look OK to me. There's no message on the SD as well.Figure 3 is after placing the EMER PWR switch to ON, things look okay to me here.Figure 4 is when the EMER PWR switch is moved back one step again to ARM. Though I'd expect the systems to be in the same state as before (figure 2), they aren't: no ON light is lit this time, this looks more correct to me, but now there's the message "BAT CHARGING" on the SD which wasn't there in figure 2 as well.So, there's a difference from which side (OFF or ON) the EMER PWR switch is moved to ARM, the result is different. Besides of the inexplainable ON light lit in figure 2, this doesn't look consistent to me.The question is only whether this is "by design" and a wanted feature or not. I didn't find enough information in the systems manual.Andreas
What I understand one have to cycle back to off and then arm or on again./ Leffe

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So they should better have made the switch going round in one direction only...It's just a bit confusing, but it seems that going to OFF is required when leaving ON is desired.Andreas

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A description of what happens when you move the Emergency Power Switch is on ELEC.30.5 in the systems manual.

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So, I simply waited not long enough, thank you for the clarification.Maybe the BAT CHARGING alert goes away after some time as well...Andreas

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