Originally Posted by
CentralPa717
Another question, unrelated to the AFCS, what exactly the function of the hot battery bus? I read something about it being for a dome light and the fire bottles.
Originally Posted by
usmc-sgt
The hot battery bus runs items that may need power while you are not there. On the -400 it runs things like the dome light, refuel/defuel panel, aft baggage light, boarding lights and a few other items. All the hot battery bus items are connected directly to that bus which is powered by the standby battery.
For the -100/-200/-300 what usmc-sgt said is mostly correct. Those items are wired to the "hot battery bus", but on the -100/-200/-300 the hot battery bus is powered by the main battery because there is no standby battery. That's why it's important to make sure the dome light and boarding lights are off when the aircraft is shut down for the night. Otherwise the main battery will drain and if the station does not have an operating GPU, there is no way to start the engines in the morning!
Originally Posted by
CentralPa717
Is it just a direct connection from the battery to these items?
Essentially, yes. The battery master, main, and aux battery switches have no control over the power to the hot battery bus. For the sake of simplicity, just think of those items as being directly wired to the main battery. I think there is a row of circuit breakers either in the cockpit or on the DC contactor box in the nose compartment that represents the elusive "hot battery bus".
Originally Posted by
CentralPa717
Also, is the APU fire bottle then connected to the hot battery bus?
Yes, page 117 of the Piedmont systems manual. "The APU fire detector and the bottle are both hot battery bus, but owing to system design, the fire bottle will only automatically discharge if there is power to the essential buses."
Originally Posted by
CentralPa717
Am I right in saying the Lav does have fire protection in the form of a fire bottle in the waste container plugged with wax that melts to activate? No flight deck control other than a fire detect light?
Originally Posted by
usmc-sgt
The lav is exactly as described but there is NO indication in the cockpit.
Lavatory has a smoke detector that "emits a high pitched tone, and causes a red annunciator light, next to the flight attendant advisory light panel, to illuminate whenever the presence of smoke is detected inside the lavatory compartment."
Lavatory fire protection is for the trash container only, as if someone were to discard something that would ignite the paper products and such that were already in the trash. This is the fire bottle with the wax-type plug that you speak of, which will discharge when the temperature becomes too hot.
There is no flight deck control for the lavatory smoke detector or fire bottle in the trash container.
The "fire detect light" is a single light module in the lowest row of red warning lights on the caution panel. The "check fire detect" warning light only illuminates at the same time as the master warning, and directs the pilot to look up on the overhead panel to determine if the APU Fire warning light, or an Engine Fire warning light is illuminated. The lavatory smoke detection and fire protection have nothing to do with the check fire detect warning light.