Obviously it depends on how good your main battery is, and how good the ECU backup battery is. How long could one expect?
Is there a process for installing a backup alternator?
30 Minutes (dedicated ECU B also good for 30 minutes).
Had this happen….in IMC. You go looking for a place to land pretty quick and the essential bus is really just for the essentials.
Never understood how you can get certification with electronic ignition and only one alternator.
The main battery is good for at least 30 mins running all IFR equipment incl. the engine. After the main battery has run down, the backup ECU battery will run the engine for another 30 minutes. So even if you do not reduce the electrical load after an alternator failure, the engine should run for 1+ hour. Assuming, of course, that both batteries are charged when the alternator is lost. Charging state of the backup battery is checked during the automated engine-prop run-up.
Yes, the charging state of the backup batteries is checked in ECU tests at 75% thresholds for a pass, tough I would be less optimistic on having a spare 1h (or even 30min, so landing ASAP) even when switching non-essentials
On IFR certification, I also never understood why you get SEP certified as they rely on one engine only (just joking but I think showing 1h reserve should be plenty to sort things out whatever the issue on typical GA IFR/VFR missions: engine, electrics, pax, envirement…) those who fly more than 2h in IMC will need load of safety nets and gadgets…
