A V and an Ultra without freon air? That's very rare. I looked into perhaps 50 of them for sale and not one lacked freon air. While it was technically an option, very few left the factory without it.


True, but passengers inside a cold cabin, which no wind now, don't seem to suffer as much as in a very hot cabin. Also, in GND mode on right engine, it heats up the cabin quite quickly.

My ACM puts out about 80 C air at maximum heating, ~175 F. Doesn't take long!

Mike C.

I have spare caution panel light positions. I bet I could wire something like that up in my plane as a minor modification.

Mike C.

This is a big benefit of an APU and QPM in a 24, assuming you have a (second) pilot. Owner flown single pilot, waiting on one’s self so maybe not a huge benefit.

As far as PC-24 operators, you’ll find it all over the map for QPM use. Some never use it, some use it a lot it for all the benefits in the last two pages. QPM uses a little more fuel than a traditional APU around 120pph, but the benefit is there is no additional engine to maintain and Williams does not charge TAP Blue time while in QPM. There are no time limits with its use except that after exiting QPM mode, you must wait 2 minutes before shutdown. For your passengers waking up to the plane, QPM noise level is also reduced significantly vs at idle. In addition, the power levers don’t respond while in QPM so no one can accidentally bump a PCL and move the plane.

Honeywell is working on a “micro APU” that is light enough to use in small jets and turboprops. I can see Pilatus offering this as an option in the PC-12 in the future.

https://aerospace.honeywell.com/us/en/l ... siness-jet

We do exactly the same thing in the Phenom 300 with a GPU. Our passengers never wait for us to get the airplane ready, 30 minutes prior to departure the GPU is on, the avionics are configured, the air is on in the summer.

We can’t get heat in winter but we load a couple of hundred extra pounds of fuel and run both engines for 10-20 minutes if it’s really cold, not a big deal.

Over the life of the airplane the apu it is pretty costly - consider the price of the apu, mx, and fuel burn.

Are they nice, absolutely, required to keep the pax from waiting, warm, or cold, absolutely not.

Brad

Can you explain why?

Seems like extra work to start it, monitor it, and maintain it. Probably some number of pages of extra procedures, normal and otherwise.

So where is the benefit?

Mike C.

I feel like we’ve stumbled into another version of the good ol’ single vs. twin debate…

Lol

Yes, we just about have.

The Best Light Jet is... one without an APU. Otherwise, it's not a light jet.

So the primary advantage is setup of stuff prior to engine start and keeping all that active during start.

I do think that is useful.

To that end, I've been wondering how I could do the same without an APU. That is, be able to power up avionics, get ATIS, set flight plan, etc, and then start the engine without disrupting the setup.

There are obviously electrical ways to do this such as a small auxiliary battery for the avionics, but I am wondering just how bad it would be to do an engine start while the avionics are on. I may hook up an oscilloscope to the avionics bus and check out the start voltage profile and spikes during such an event. I suspect they are not that large and tolerable.

A big advantage might be to start one engine for taxi and only start the second when ready for takeoff. This would save brakes as well as fuel.

I could see starting the right engine for use as an APU. Setup things, load passengers, taxi to runway, then start left and go fly.

If keeping avionics on can be done during start, then I have most of the advantages of an APU without the disadvantages.

Mike C.

With modern avionics, LED lighting, etc, your best “auxiliary battery for avionics” is probably just ship’s battery. If your battery is in good condition you should be able to program avionics with no real difficulty then start engines.

I occasionally do this in the Mits if I don’t want to bug people in the FBO nearby. The Garmin avionics seem just fine.


Seems to me as a single pilot that you would want to be settled at the pilot controls before starting an engine. Load pax after engine start might be problematic if they need any kind of assistance (eg close door properly, who knows what else….). You can’t (shouldn’t!) leave the cockpit empty with an engine running.

Particularly in the Citation where cross gen starts are the norm for the second engine.


Agreed, this would only be with experienced folks who know how to do all that.

The park brake on Citation is quite good, too, but agree that one should never be out of the cockpit with even idle thrust being generated.

Mike C.

So the primary advantage is setup of stuff prior to engine start and keeping all that active during start.

I do think that is useful.

To that end, I've been wondering how I could do the same without an APU. That is, be able to power up avionics, get ATIS, set flight plan, etc, and then start the engine without disrupting the setup.

There are obviously electrical ways to do this such as a small auxiliary battery for the avionics, but I am wondering just how bad it would be to do an engine start while the avionics are on. I may hook up an oscilloscope to the avionics bus and check out the start voltage profile and spikes during such an event. I suspect they are not that large and tolerable.

A big advantage might be to start one engine for taxi and only start the second when ready for takeoff. This would save brakes as well as fuel.

I could see starting the right engine for use as an APU. Setup things, load passengers, taxi to runway, then start left and go fly.

If keeping avionics on can be done during start, then I have most of the advantages of an APU without the disadvantages.

Mike C.

You can start the Mustang with NXi avionics on, no problem. Didn’t work before NXi, but now it does fine. The NXi avionics draw is very small

Why would you want the added cost, weight and complexity of an APU? Besides there are no SP Jets with APUs. If you want to run the AC just plug a cart.

I didn't know that. No one told me.. Is this a change in the checklist or just new SOP?

I didn't know that. No one told me.. Is this a change in the checklist or just new SOP?