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What does the "EMERG BATT switch" and the associated phrase "(if starting battery installed)" mean? I could not understand what the "EMERG BATT switch" and its associated expressions (if starting battery installed) in the "INFLIGHT ENGINE RESTART" procedure in the emergency section of the Tecnam P2006T aircraft mean. Because even though I scanned the entire AFM of the aircraft, there is no information about the "EMERG BATT switch", which is referred to as the backup battery. Also, I didn't understand what was meant by the expression (if starting battery installed). I think I need a detailed answer. I am attaching to the question the image of the page where the procedure is and where these statements are mentioned.

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    $\begingroup$ This is not an answer, but from what I read online, the FAA required a second battery to be installed, specifically for in-flight restart. So this instruction seems to say... if you have the second battery installed, in case of first in-flight restart unsuccessful, retry with the second battery connected. It's likely a problem of insufficient current, and the two batteries are connected in parallel to prevent the voltage to drop when the starter is activated in the second attempt. The answer is likely in the FAA document, but I was no able to get it. $\endgroup$
    – mins
    Commented Sep 11, 2023 at 17:22
  • $\begingroup$ I understand and agree with everything you say. However, there is an article in the AFM document that I edited above. Do you think this means "Starting Battery = Emergency Battery"? $\endgroup$
    – pilot162
    Commented Sep 11, 2023 at 17:53
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    $\begingroup$ I think yes. I found a reference for the modification: MOD2006/049 “Engine Starting Battery”, but not the details. This mod is referenced in the FAA type certificate. And by the way the text you ask for is also applicable to single and dual generator failure procedures. $\endgroup$
    – mins
    Commented Sep 11, 2023 at 18:01
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    $\begingroup$ I think you have discovered one of my personal peeves: When manufacturers and technical writers use different words to describe the same thing... $\endgroup$ Commented Sep 11, 2023 at 18:14
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    $\begingroup$ I get confused when the same thing is named differently and it drives me crazy too :) $\endgroup$
    – pilot162
    Commented Sep 11, 2023 at 18:27

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While I have not worked on this type of aircraft, I believe that it has 2 separate batteries. One battery is used just for the starters. The second battery supplies power to the various aircraft systems such as lighting and avionics.

During normal operations the generators charge both batteries, but only the first battery is used for the starters and only the second batteries the rest of the systems. Placing the battery switch to emergency allows both batteries to power the starters. That way if something has happened to first battery, the second battery might still be able to restart the engines.

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  • $\begingroup$ The point that I do not understand here is which battery we call emergency battery is? Engine Starting Battery or Main Battery? If we think that it is the Engine Starting Battery that feeds the starters to start the engine, is our emergency battery here the main battery? $\endgroup$
    – pilot162
    Commented Sep 11, 2023 at 18:37
  • $\begingroup$ I also added the backup (emergency) battery switch to the question. And am I supposed to understand that the function of this button is to connect the main battery to the engine starters since the engine starter battery cannot start the engine? $\endgroup$
    – pilot162
    Commented Sep 11, 2023 at 18:40
  • $\begingroup$ Motorhomes have a similar system. It allows a second battery to be available for a re-start of the engine. $\endgroup$ Commented Sep 11, 2023 at 20:26
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    $\begingroup$ @pilot162, I think the reverse is true: That the main battery starts the engines normally, unless you flip the switch to connect the Starter/Back-up/Emergency battery. I say this because of the procedure that says "if starting battery installed..." This makes it sound like an option, that perhaps not all aircraft have one installed. $\endgroup$ Commented Sep 11, 2023 at 22:37
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    $\begingroup$ "One battery is used just for the starters", I think this is incorrect. The two batteries should be in parallel, but the second is normally switched off. This second battery is switched on in case of electric generator failure and/or for the second attempt of an engine inflight restart (this case also implies a lack of generator). $\endgroup$
    – mins
    Commented Sep 12, 2023 at 13:04

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