Having nothing better to do, I took a very close look at the POH recently (the A revision) and in the course of passing on the things I found (most of which had already been fixed) the doc guy mentioned that there had been considerable confusion about the load shedding stuff, and that section was being rewritten. I vaguely recall that the prototype had a switch on the panel bolster, but this doesn’t exist in the production model. Instead, there’s a non-essential bus breaker that you can pull that turns off all of the non-essential stuff (study the electrical diagram carefully…)
I agree that the electrical diagram in the POH leaves much to be desired. It’s not only confusing, but also inconsistant. For example, most CB’s are associated with a power source, but some just “float” with no indication of where they get their power. I’ve studied the diagram carefully and can’t seem to find the “Non-Essential Bus” CB you mentioned. I just got the POH recently so it should be a fairly recent edition (Cchange A1, actually).
This brings up the larger question of POH shortcomings and inconsistancies. For example:
In the electrical emergency procedures section there’s no mention of how to isolate the essential busses.
In the Range / Endurance Profile tables (Figure 5-16) the note says “Fuel Remaining includes 10.1 gallons for 45 minutes reserve at 75% power.” I’m not quite sure what that means. Does it mean you really have 10.1 gallons MORE than the fuel remaining shown in the table? Or you have the amount shown, but you have to subtract 10.1 gallons mentally? I presumed it was the former. To try to confirm this I looked at the starting fuel in the table which is 46.9 gallons. So it indeed looked like they’re taking the reserve off the top and that you really have the fuel shown plus the reserve. BUT the ususable fuel, according to the POH, is only 56 gallons. 56 minus 46.9 = 9.1, not 10.1 . What gives?
It’s not that 1 gallon is all that important, it’s just that these inconsistancies reduce confidence in the POH and make figuring out what it ACTUALLY means difficult.
I should say that I’m an ex-military pilot and the Cirrus POH is the first civilian one I’ve studied carefully. I realize that it very well may be light-years ahead of other POH’s and that I might be expecting too much.
Joe Mazza
I am glad someone else can’t find the non-essential bus circuit breaker in that diagram. If someone knows where it is please let us know.
I agree that the electrical diagram in the POH leaves much to be desired. It’s not only confusing, but also inconsistant. For example, most CB’s are associated with a power source, but some just “float” with no indication of where they get their power. I’ve studied the diagram carefully and can’t seem to find the “Non-Essential Bus” CB you mentioned. I just got the POH recently so it should be a fairly recent edition (Cchange A1, actually).
I mentioned that some CB’s “float” on the electrical diagram with no indication of their power source. After looking again at the diagram there is only one “floating” CB (Standby Vacuum) and if you look in the vacuum section, per the note on the diagram, it does show the power as coming through a 25 amp fuse in the MCU. [But why not show that on the electrical diagram?]
Joe
I agree that the electrical diagram in the POH leaves much to be desired. It’s not only confusing, but also inconsistent. For example, most CB’s are associated with a power source, but some just “float” with no indication of where they get their power. I’ve studied the diagram carefully and can’t seem to find the “Non-Essential Bus” CB you mentioned. I just got the POH recently so it should be a fairly recent edition (Change A1, actually).
This brings up the larger question of POH shortcomings and inconsistencies. For example:
In the electrical emergency procedures section there’s no mention of how to isolate the essential busses.
In the Range / Endurance Profile tables (Figure 5-16) the note says “Fuel Remaining includes 10.1 gallons for 45 minutes reserve at 75% power.” I’m not quite sure what that means. Does it mean you really have 10.1 gallons MORE than the fuel remaining shown in the table? Or you have the amount shown, but you have to subtract 10.1 gallons mentally? I presumed it was the former. To try to confirm this I looked at the starting fuel in the table which is 46.9 gallons. So it indeed looked like they’re taking the reserve off the top and that you really have the fuel shown plus the reserve. BUT the usable fuel, according to the POH, is only 56 gallons. 56 minus 46.9 = 9.1, not 10.1 . What gives?
It’s not that 1 gallon is all that important, it’s just that these inconsistancies reduce confidence in the POH and make figuring out what it ACTUALLY means difficult.
I should say that I’m an ex-military pilot and the Cirrus POH is the first civilian one I’ve studied carefully. I realize that it very well may be light-years ahead of other POH’s and that I might be expecting too much.
Joe Mazza