APU questions

[Barthandelus 1]

Hi, All! I have a coupla question re the APU:

 

1. Need to click to 'start' a few times for the fault light to go - tried moving the middle APU bleed switch to reset, then back down. Eventually, it bites, but takes a few attempts.

 

2. So to practice the shutdown procedure, im start from C&D, then shutting down. But again, the APU wont start. APU Bleed is on, flick the switch to Start. Low Oil Pressure and Fault is on. Cant get it to fire at all.

 

All failures are off.

 

3. Also, once the engines are on, how long should the APU take (the EGT dial by the APU switch) to go to zero? Is it linked to the Packs at all?

 

4. Is that dial the only way to monitor the APU? Is there an N1 or N2 reading somewhere for it?

 

Can someone please help me? Thanks for your time.

[A320FAN 370]

 

 

You have connected the GPU (Ground Power Unit) via FMC FS ACTIONS/Ground Connections ?

APU: This is a turbine that powers the aircraft

 

Is it linked to the Packs at all?

No. You can connect via FMC FS ACTIONS:Ground Connections/ASU (Air supply Unit). when the packs are inactive.

APU takes about 1 minute.

[Jazz 1,047]

1. When you switch to start it takes time to spool up an show temps on the guage. Switch once and wait a minute or even two. Make sure you have ground power connected.

 

2.Check ground power

 

3.Quite a while before it drops. (think about it...it would take a while)

 

4.Tis all you need.

 

Regards

[Barthandelus 1]

Thanks for your help guys. Yep, its power is connected in the FMC.

 

James, what you said about #2 - Interesting to know that the APU needs ground power even tho the engines are on. I thought the APU was started during taxi from the runway to the gate?

[rsvit 16]

Have you checked fuel quantity (I mean configuration - fuel in different tanks, crossbleed, fuel pumps)? What about APU fire switch?

If battery is charged enough, GPU is not needed to start APU.

 

1. Need to click to 'start' a few times for the fault light to go

 

FAULT light shouldn't be illuminated during normal start. APU is malfunctioning for some reason.

 

APU Bleed is on,

 

I would recommend to turn on APU bleed at least 1 minute after APU is started.

 

Also, once the engines are on, how long should the APU take (the EGT dial by the APU switch) to go to zero?

 

60 sec.

 

Is it linked to the Packs at all?

 

[Jazz 1,047]

Thanks for your help guys. Yep, its power is connected in the FMC.

 

James, what you said about #2 - Interesting to know that the APU needs ground power even tho the engines are on. I thought the APU was started during taxi from the runway to the gate?

 

Quite right fella I miss read your post there. Of course no need for ground power in that case. Most interesting it won't start. Would not mind seeing a pic of your overhead panel in this instance.

[Fabo 213]

James, what you said about #2 - Interesting to know that the APU needs ground power even tho the engines are on. I thought the APU was started during taxi from the runway to the gate?

 

APU does not need ground power. How did anybody ever come to that conclusion.

 

So, once again, from beggining to end:

 

-Coming at a cold and dark airplane, no GPU available. First thing you do, turn the battery on, very next thing, flight the APU switch to START. It is springloaded to go back to run, but the sequence has begun. Wait a moment, you should see it start, EGT will rise, any warning lights go off. Couple seconds later, you can connect APU electrics. Blue light will come on, now connect both sides and go about your business.

 

-You should not connect APU air right after startup, give it a bit of warmup time (not needed for elec), a minute or so.

Then you connect APU air, open packs, ISOL valve open.

 

-when you start the engines, do it the normal way, turn off packs, start them up, connect everything up. As soon as APU is not loaded by elec and air, flick the switch to off. Cooldown countdown will start and APU will turn itself off after a moment.

 

 

 

-after landing, flick the APU switch to start, should be ready as you park.

 

-connect the APU GEN, and if needed, air, shut the engines down.

 

-carry on with shutting the aircraft down, shut down IRS, HYD pumps, etc.

 

-when everything is shut down, disconnect APU from the elec network and flick the switch off. Wait until it shuts down, then turn battery off and you have a C&D plane.

[A320FAN 370]

-Coming at a cold and dark airplane, no GPU available.

If, you can add Microsoft Games/Microsoft Flight Simulator X/PMDG/PMDG 737NGX/PanelState NGX CLDDRK 'file SAV' and you replace 0 with 1.

[VIPERGTSR01 22]

To confirm Fabo above the APU can start straight off the bat (assuming it isn't flat) no need for any AC source at all.

 

Click the APU to start, it will spring back to run and leave it. the low oil pressure light will come on (fault light stays off unless it is faulty), EGT's rise and oil press light goes off, as APU settles AC and bleed will become available. Be a little patient, give it time to start before hitting start over and over.

[davierosoft 13]

I can add: If apu was already started and shut down, let it cool some minutes before doing another start or FAULT light will appear. FAULT will be reset if you switch it back to off, and wait more.

 

PS:

It is useless to see air conditioning switches.

APU is electrically started, either from battery or AC power if present, the APU bleed is useless untill APU is 100% running.

[Barthandelus 1]

Thanks all for your help, definately made a difference.

How long should i wait before starting the APU after shutting it off (so i can practise shutting the plane down) Im still getting the Fail light, even after leaving the plane running for 10 minutes. I flick the APU BLEED switch to the down position, then the APU switch to Start. Still get the Fail light. My overhead looks exactly the same as the default one does when the plane loads.

 

Also, from C&D, the APU will only start if ground power and Air Start unit is connected. I did notice the BAT DISCHARGE light comes on as soon as i turn on the battery. Setting the dial to STBY PWR works, tho.

[kevinh 409]

The APU bleed switch has nothing to do with APU start and shutdown logic. Its position is irrelevant and thinking about it is only confusing you. Similarly the air start unit. The APU starts from the battery. Without AC power it looks like nothing is happening, but connecting the GPU isn't necessary for an APU start either. Make sure the battery is fully charged though.

 

As for how long to wait before you can shutdown the APU, no need to wait at all. In the aircraft, if you had used APU bleed then you should run the APU with bleed off for a minute before shutdown. However in the sim this is not necessary.

[davierosoft 13]

The fail light could be already on due to a failure in your attempt to start the apu too early. Check the FMC for active failures.

Now, to practice:

Load the default C&D condition

Turn on the battery, BAT DISCHARGE will always come on, if it comes on in few seconds, more seconds, or instantly, it is related to power needings of the aircraft.

You can switch off the STBY PWR to save some amps.

Switch the APU BLEED to OFF (UP) it is not required for starting, neither it will be on until APU is fully running, so, it is useless to have it on. APU BLEED is the last thing you touch after APU started.

Now, switch the APU master switch to ON, then, START and release the switch. Low pressure light comes on, and after few seconds you will see EGT rising.

When generators are avaiable (ready to supply) the APU is started, power the aircraft with APU GEN (both switches) then apply an AC fuel pump to feed the APU and turn the bleed on as required.

To shut down (to a complete c&d)

Turn off the fuel pump

Turn off the bleed

Put the APU switch to OFF

What will happens:

APU will start to unload, this means that electrical and bleed systems will be cut if you didn't previously.

After a minute APU will shut down automatically, the APU air intake door will close.

Let it cool for at least 5 minutes before starting again.

 

The APU bleed switch has nothing to do with APU start and shutdown logic. Its position is irrelevant and thinking about it is only confusing you. Similarly the air start unit. The APU starts from the battery. Without AC power it looks like nothing is happening, but connecting the GPU isn't necessary for an APU start either. Make sure the battery is fully charged though.

 

As for how long to wait before you can shutdown the APU, no need to wait at all. In the aircraft, if you had used APU bleed then you should run the APU with bleed off for a minute before shutdown. However in the sim this is not necessary.

I had some apu failures by starting the APU when it was just previously shut down, PMDG simulated it, don't know if can be disabled by disabling failures.

[Barthandelus 1]

Seem the BAT DISCHARGE is coming on instantly, and stays on, so have have to use ground. Restarting FSX doesnt help.

Once the engines are running, i switch the APU off. Once it is off however, i cant get it back on, even if i leave it 10 mins

 

Edit - set battery life to indefinate in FSUIPC; a little bit cheaty, but it helps until i can get used to this.

[davierosoft 13]

BAT discharge doesn't mean that battery is discharged.

Check battery voltage, if more than 22V it is able to start the APU.

Forget about that light itself.