Hello Your technical advise is kindly asked: When on ground and connected to both external power buses I could not start the APU in several different FS sessions. I always had to start the main engines with ground air connected. I guess that the Air, Fuel, Elec and Hyd systems are supposed to be in AUTO mode as they were. Then, I found out that I could start the APU as soon as I switch the Fuel panel on the Overhead to Manual mode and switch on the fuelpumps. I don't understand this repeatable behavior. Anyone please comment on this?Thanks in advance. Tom Castelberg

Are you pressing the APU power button on the forward overhead panel? It should flash avail when pressed.

Hello Your technical advise is kindly asked: When on ground and connected to both external power buses I could not start the APU in several different FS sessions. I always had to start the main engines with ground air connected. I guess that the Air, Fuel, Elec and Hyd systems are supposed to be in AUTO mode as they were. Then, I found out that I could start the APU as soon as I switch the Fuel panel on the Overhead to Manual mode and switch on the fuelpumps. I don't understand this repeatable behavior. Anyone please comment on this?Thanks in advance. Tom Castelberg

Tom, please post a picture of the overhead panel when you see this problem again.

Hello Your technical advise is kindly asked: When on ground and connected to both external power buses I could not start the APU in several different FS sessions. I always had to start the main engines with ground air connected. I guess that the Air, Fuel, Elec and Hyd systems are supposed to be in AUTO mode as they were. Then, I found out that I could start the APU as soon as I switch the Fuel panel on the Overhead to Manual mode and switch on the fuelpumps. I don't understand this repeatable behavior. Anyone please comment on this?Thanks in advance. Tom Castelberg

Tom,Works correct overhere from a cold and dark cockpit. (FSX) With all systems in AUTO.In order not to miss an important step, may I suggest to have look in the FCOM:- Cockpit PreparationPages NP.20.1 -- NP 20.6Hope this helps you further.Regards,Harry

Thanks folks. Yes, I push the APU button on the forward Overhead (ELEC section). The AVAIL lights flashes about five times, then ceases to flash. SD Engine display shows APU coming to live with N1 going up to 5 and then goes back to 0 and APU indications vanish. Nothing happens until I set the Fuel panel to Manual and start the APU again. Funny thing. I'm using FS9. What's up? Thanks Tom

Tom, screenshot of the overhead panel please

Thanks folks. Yes, I push the APU button on the forward Overhead (ELEC section). The AVAIL lights flashes about five times, then ceases to flash. SD Engine display shows APU coming to live with N1 going up to 5 and then goes back to 0 and APU indications vanish. Nothing happens until I set the Fuel panel to Manual and start the APU again. Funny thing. I'm using FS9. What's up? Thanks Tom

Tom,Also my FS9 version is working correct here.Wonder what your pre APU start selections are.As Bryan suggests, a screenshot may help.Harry

Also wondering if you have your refuelling going. From experience if you are refuelling (from the FMC menu and the 'truck' is 'pumping' to your tanks) then the APU will not start. will need to wait till the blue "Refuelling" text is removed from the ECIAS before APU can start.On the other end, you can't start APU while Engine 2 is delivering air to the Pack2. either turn packs to manual and shut down centre, or simply shut down centre engine before you start APU.Trent.

Also wondering if you have your refuelling going. From experience if you are refuelling (from the FMC menu and the 'truck' is 'pumping' to your tanks) then the APU will not start. will need to wait till the blue "Refuelling" text is removed from the ECIAS before APU can start.On the other end, you can't start APU while Engine 2 is delivering air to the Pack2. either turn packs to manual and shut down centre, or simply shut down centre engine before you start APU.Trent.

Should the tailtank also contain fuel? The APU draws it's fuel from the tailtank.

Trent, At the moment I want to start APU I don't have any packs or engines running. I try to make a screenshot next time. RegardsTom

Should the tailtank also contain fuel? The APU draws it's fuel from the tailtank.

The APU draws it fuel from tank 2 (center).

Also wondering if you have your refuelling going. From experience if you are refuelling (from the FMC menu and the 'truck' is 'pumping' to your tanks) then the APU will not start. will need to wait till the blue "Refuelling" text is removed from the ECIAS before APU can start.

It's indeed not smart to switch main electrical power sources during refuelling.But there is no system logic preventing this, so starting the APU should be possible if you want to.

On the other end, you can't start APU while Engine 2 is delivering air to the Pack2. either turn packs to manual and shut down centre, or simply shut down centre engine before you start APU.Trent.

Also Eng2 /Air to Pack2 does not prevent an APU start. (eg. during taxi-in.)Regards,Harry

Trent, At the moment I want to start APU I don't have any packs or engines running. I try to make a screenshot next time. RegardsTom

Tom,In a cold and dark cockpit, basically you only need this:- Battery ON- External Power OFF or ON (to get APU parameter indications)- APU ONIf this does not work for you, there must be something wrong in your setup.Regards,Harry

Im sure thats the problem. You definately cant start the APU while you are refueling. If you must use the APU, start it before you start the refueling

Im sure thats the problem. You definately cant start the APU while you are refueling. If you must use the APU, start it before you start the refueling

Yes Bryan, it is. Just tried it in the simulation. Can't find any reference to this in whatever (sim or real) manual.Regards,Harry