Page 28 - Volume 15 Number 10

“ ... in the event of a dual generator failure, this newer electrical system will automatically shed ... electrical load to prolong the time your battery can supply more critical items. ”
A more likely malfunction is that one of the three annunciators did not appear when we used the BUS SENSE switch’s TEST position: Probably a bad HED.
A note to F90 operators: In the electrical system installed on earlier F90s – the very first attempt Beech made to use this newer system – some problems exist. I won’t call them “mistakes,” but the temptation is strong to do so! The two test switches are not labeled the same as I have described although they operate identically. The voltmeter is missing two positions, including the center bus. The annunciators are really weird! Instead of the simplicity of separate Left and Right GEN TIE OPEN lights, you have a single GEN TIES OPEN light. Notice that its plural, not singular. When both ties are open – such as before start and after we activate the BUS SENSE OPEN switch – the annunciator is correct in being plural. But
during engine starting. All three HEDs are “desensitized” – they take a coffee break and won’t work – whenever either starter switch is on.
Back to the test procedure: Since the HEDs react instantaneously, the BUS SENSE switch should only be momentarily depressed – I used the word “tap” above – and then released. The HED can be damaged if it senses the strong magnetic field too long.
After we “tap” the switch, all three HEDs should cause their respective
relays to open, and we should now see three yellow annunciators: the same two we saw before – Left and Right GEN TIE OPEN – and also now BAT TIE OPEN. With these three relays open, the center bus should be totally isolated from the three sources of power, two generators and the battery. To verify that it is indeed “gone,” we again direct our attention to the voltmeter and confirm that there is zero voltage on the center bus. If voltage is still showing, then one of our annunciators is lying.
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26 • KING AIR MAGAZINE
OCTOBER 2021