Master Caution/Elect systm/EPU
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After reading the manual I think I have figured out my issue but I am not sure.
Ocasionally I get a Master Caution and elect system issue well after take off and EPU lights illuminate by the main power switch.*I always pull the pin when at the ramp.
My issue might be because I periodically pull them prior to engine start and in my thinking that might cause the EPU to run and deplete which may be why it comes on later in flight ?.
I havn’t had enough time to test this was hoping one of you may know what is causing this as it does not happen on all my ramp start flights.
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Yep, you’re not supposed to pull the pin before engine start. It’s an excellent way to send the ground crew to the hospital.
Then again, maybe they don’t have insurance and need an excuse. Case by case basis.
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Thanks. I took a long read of the -1 and seems a engine start in BATT will also cause a ELEC SYS.
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Thanks. I took a long read of the -1 and seems a engine start in BATT will also cause a ELEC SYS.
It is s a little more complex.
The ELEC SYS caution light will illuminate when one or more o ELEC control panel lights illuminate. The caution light will prompt you to check the ELEC control panel and take the appropriate action depending on which electrical system has failed. The master caution light will illuminate whenever a caution light is illuminated, with the exception of the IFF caution light.When you place the MAIN PWR switch to BATT, or MAIN PWR, the MAIN and STBY generators are offline , so those lights will illuminate. ( hence the ELEC SYS caution).
Sticking only to electrical failures ,the EPU will run when the MAIN and STBY generators are offline. When the jet is in a WOW state, and the safety pin is removed, there is one more “flag” that needs to be true for the EPU to run, and that is the throttle position to be in idle or above.
That is the reason why you don’t see the EPU running when you remove the safety pin while only battery power is available.
As soon as you move the throttle from the OFF position, the EPU will run.
It is also the reason why the EPU dose not run when you shut down the engine .The throttle is moved to OFF before the MAIN and STBY generators go offline as the engine spools down.
Normally, engine bleed air is used to maintain EPU operating speed. When bleed air is insufficient, hydrazine augmentation automatically occurs, and eventually it will run out after prolonged use.I hope its clear now why there is a EPU safety pin, and when you should remove it.
Now about the EPU run lights ,it trust that your referring to the EPU GEN and EPU PMG. You say that the EPU lights will occasionally illuminate. I think you may have stumbled on a bug, meaning that at least, the EPU GEN light should always illuminate in you scenario.
If hydrazine is depleted, and bleed air is insufficient, the generator control unit will trigger an EPU generator fail indication. Since the EPU has been commanded on but the EPU generator is not providing power to both emergency ac buses, the EPU GEN light will illuminate.
Replicating your scenario, after hydrazine depletion, the EPU GEN/PMG did not illuminate for me. The only way I could make them illuminate, is if I cycled the EPU switch. Since the EPU was already activated, I should have at least had the EPU GEN illuminate.
The EPU PMG is a bit tricky and I’m not sure if it would illuminate in this scenario. From the EPU diagram, I can see that the EPU PMG fail indication comes directly from the converter/regulators, that are already receiving power from the primary FLCS power source, the FLCS PMG.
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Awesome reply man and thank you for taking the time to write that. I understand these functions about as much as a armchair pilot haha. You are correct it was EPU/EPU PMG. I will try and see if I can replicate the issue. Being naive I cleared the test page (without taking note),and hit the caution reset on the electical panel and resumed my entire flight,and only after reading the -1 realised there are files logged that would have been more helpful. It has happened to me about 3 times in total and very randomly- I will try and replicate it and post them. My ramp starts are a succesful failure (Apollo 13 qoute) I have not studied the ramp start in 3 years and got stuck in my ways.