Here is a GPU experience and question:

In the early Citation X days, a mechanic and I were out at the Cessna fuel pits, hooked up to the ground power, doing fuel system functional tests.

Everything was going good until all of a sudden, the aircraft died electrically. Unbeknownst to us, the ground power had blown its circuit breaker (not an aircraft breaker) and we were on the battery until it died.

I asked around later, and there is no apparent indication of this situation other than maybe monitoring the voltmeter closely.

Is this typical of other models on ground power?:

Yes, the voltmeter is the only way to tell when the GPU is providing power or not.

Basically, battery is 24-25 volts, GPU is 27-28 volts, typically.

It could be possible to add an indicator light that you are on GPU (tied to the detector pin on the GPU plug), but I have never seen that personally.

Mike C.

Starting from GPU is better for the battery (and the engine) *IF* the GPU is doing its job.

The high current during start does cause some damage to the battery cells that accumulates at each start.

Some feel the high current start does some good to the battery, but there's no theory behind that I know of.

The main reasons batteries have short life have to do with improperly set voltage regulators (either undercharge or overcharge will shorten life), or letting a battery get deeply discharged. Those two conditions will cause a lot more damage than starting so they should be avoided.

Mike C.

A conversation about GPU's on a light jet thread.

haha seriously.

What Light jet has a APU? I don't think any. Edit- I assume you meant APU, not GPU.

We are loving our 501sp Eagle II. for overall value per seat its hard to beat. Love not worrying about payload or a piston engine deciding to blow up at any minute. Never knew take offs could be so relaxing and fun.

Mike

Piaggio has that actually - when power from GPU hits the plug, green light goes on on annunciator panel. I am continually surprised by how many line guys flip on the power before I ask them to.

Piaggio has that actually - when power from GPU hits the plug, green light goes on on annunciator panel. I am continually surprised by how many line guys flip on the power before I ask them to.

I think you meant APU

in the king air the external power indicator light turns on when you connect the GPU, even if the GPU is not turned on- you can then check the voltage on the external to see if there is any present, if there is, then you flip the switch to close that solenoid and enable that current to enter the plane

my point being, if the line guys flip it on, you still have to push a button inside the plane to enable it, the problem that I have found is that if the EXT POWER switch is turned on, then the AC system can try to run off battery (bad!), so if you have your AC running or your heat running, and someone turns the ground cart on, bad things occur

is the Piaggo different?

I think you meant APU

Most. I’ve flown the II, V, and Ultra, and not one of them had Freon air.

A vapor cycle system also only helps when it’s hot. It does nothing when it’s cold.

Light jets don't have APUs, quite mode or "APU" mode on PC24/P300E not as useful as the marketing team advertises...thread over

Have we talked about the MU2 yet?

I’ve had both GPU and APU fall off line without any warning. Thankfully I’ve been able to catch it when it does, but there have been two times recently where it almost bit me in the backside. In the CJ, was hooked up to one of those JetPorter egg shaped GPU’s that all the big players seem to just love. I’ve had nothing but heartburn with them and don’t trust them like the old Hobart units. Anyway, we were at Boca on the cart with the air running. I’m outside chatting with one of the line guys and notice the nav light on the wing blink. Odd, says I, so I go check the gages to find the GPU had dropped off line and the battery was so depleted in a matter of minutes, I was a gnats hind end from being stuck. The other time was just last week in one of the Astras - APU up and running, fat, happy, and sassy in the cockpit waiting on ground to give me the clearance and look down see the APU Gen had dropped off line and thrown a fail fault. No biggie, simple reset of the Gen and we’re back in business.

Point is, neither is fool proof and complacency with either will cause embarrassment and heartburn. My experience, and SOP, is don’t leave either unattended for more than a few minutes, and if we do run into the fbo, always go check the gages before anything else when we come back out.

Brian - thanks for the kind words on our little fbo. I’m mighty proud of my folks - it’s them that make it what it is. We are fighting an uphill battle and don’t have much to work with, but my team gives it everything they’ve got and they do it with heart, and I can’t ask for more than that.

Light jets don't have APUs, quite mode or "APU" mode on PC24/P300E not as useful as the marketing team advertises...thread over

Have we talked about the MU2 yet?

Yep, and topping or circumnavigating around weather etc etc. The lower stress factor is worth it all by itself.