Power loss during engine start up

[jumpjet]

Hello

May I ask why there is power loss to the Essential Avionics DC Bus as each engine starts? It seems a strange behaviour.

Where the default GPS 530 seems to be powered from the left avionics switch, which also loses power on engine start and therefore reboots, it does no harm to any pre-entered flight plan.

However I now have the Reality XP GTN750 added as a plugin, and used as a pop-up window. The power for this (in the Saab's case) comes from the Essential Avionics DC Bus, and the flight plan is lost when it reboots after each engine start. I realise that I could save the flight plan before engine start, but I'd rather not do that as it will contain runways and procedures which suit this flight only.

So my question is not really about the GTN750 and flight plan saving, it's more to with why an essential dc bus is being shedded by an engine start. It seem to be counter-intuitive, and a bit of a misnomer to call the bus essential. It doesn't matter whether you do a GPU start or a battery start

Cheers

Edited September 3, 2018 by jumpjet
grammar

[JGregory]

2 hours ago, jumpjet said:

So my question is not really about the GTN750 and flight plan saving, it's more to with why an essential dc bus is being shedded by an engine start. It seem to be counter-intuitive, and a bit of a misnomer to call the bus essential. It doesn't matter whether you do a GPU start or a battery start

This is exactly how the real aircraft behaves.  The power is removed from the those busses to protect the avionics instruments from electrical spikes during engine start.

[jumpjet]

24 minutes ago, JGregory said:

This is exactly how the real aircraft behaves.  The power is removed from the those busses to protect the avionics instruments from electrical spikes during engine start.

Ah OK I see ............ logical but annoying

Thanks very much for the quick reply

[ALH]

59 minutes ago, jumpjet said:

Ah OK I see ............ logical but annoying

Thanks very much for the quick reply

The best way to proceed is to power on the plane, start the GPS and make flight planning and set radios and other things, shut down the avionics and make the startup. After it is done, power on again and switch on the GPS and the flight plan is kept as before.

Enjoy this beauty aircraft.

[jumpjet]

21 minutes ago, ALH said:

The best way to proceed is to power on the plane, start the GPS and make flight planning and set radios and other things, shut down the avionics and make the startup. After it is done, power on again and switch on the GPS and the flight plan is kept as before.

Enjoy this beauty aircraft.

Hi

Thanks for the reply.

Your method is fine for the default GPS supplied with the aircraft, but not with the default setup of the add-on GPS I am using.

The great news is that it's now solved, as there is a setting for the XP Reality GTN750 that allows for the GPS to be  'Always On', rather than it being powered from the essential bus

Cheers

Edited September 3, 2018 by jumpjet