Hello! I failed to run the after start checklist and forgot to connect the idg's after engine start. I took off with the apu powering both transfer busses. I also meant to turn off the apu during taxi and forgot that also. All sort of pilot error! So during climbout I turned off the apu and found myself on Battery power only. I read in the manual that if you takeoff with the apu powering the txfr busses and it then fails or is turned off, then the idg's will automatically come on line. Well this did not happen. No big deal I simply turned on the engine drive generators but I wondered why this was not modelled in the ngx. It got me asking myself "what were the developers not able to include in this simulation?" I guess this question is best answered by realworld 737 pilots. So my question is to the real world pilots that own a copy of the ngx... is there anything that in your opinion really should be added or corrected to enhance the ngx?

Could you provide the manual and page number your read this? Was it in the FCOM?

I think if you have left the GEN 1 and GEN 2 switches in the "OFF" position, you are out of luck if you shut down the APU and/or the APU GEN switches. The generators won't automatically connect if the switch is selected "OFF." If you look at 6.10.9 in FCOMv2, you will see:

#6 - GEN Switches - OFF - disconnects IDG from related AC transfer bus by opening generator circuit breaker.

#7 - BUS TRANSFER Switch - AUTO - BTBs operate automatically to maintain power to AC transfer busses from any operating generator or external power.

 

Key words are "from any operating." If the GEN switches are off, that means the breaker is open and therefore that generator is isolated from the system and for all intents and purposes is offline. #7 is a bit misleading of a statement, but if the GEN 1/2 switches are both OFF and you switch off the APU and/or both APU GEN switches, you will revert to standby power, as long as the bat has a charge and the standby power is set to AUTO.

 

If there is wording in the FCOM that says the GEN switches will automatically go to "ON," I'd like to know where that is as well.

Oddly enough there are a few mentions on example type rating tests online, but I can't find it elsewhere.

 

http://www.b737.org.uk/generators.htm makes no mention of it, and on other pages (specifically related to the electrics), it states otherwise:

There are three golden rules of 737 electrics:

1. There is no paralleling of AC power.

2. The source of AC power being connected to a generator bus takes priority and automatically disconnects the existing source.

3. A source of AC power does not enter the system automatically (when it reaches proper voltage & freq). It must be manually switched on.

Thanks for the replies guys!

FCOMv2 that came with the NGX page 6.20.5.

This is indeed a feature on the NG. At least, according to our FCOM it is, I've not had the chance to test it in real life ;-)

Adam-

 

Ryan forwarded your question along to me, since the electrical system was coded by me...

 

The function to which you refer is a "Stupid Pilot Savior" that is designed to prevent the airplane from becoming de-powered in the event that you leave both busses on the APU Generator at takeoff.

 

The system arms in the following conditions:

 

The Weight on Wheels switch is closed, the APUGenerator is providing power to the AC busses and the IDGs are BOTH offline.

 

If you take off in that condition, according to the technical specifications document against which this system was designed, the IDG's will be immediately connected to their respective busses and the APU Generator will thus drop offline. I just tested this condition and found it working without any trouble.

 

I'm not certain why you didn't get the bus transfer at liftoff- but I can only assume you had some other condition in there that disarmed the system. (Since you didn't follow the checklist in the first place- I will expect a written report on my desk by monday, please.)

 

It is interesting to note that the FCOM describes the system differently than the engineering documents. The FCOM appears to indicate that the airplane will stay on APU power until the APU generator is lost (through failure or shutdown) but our model does not currently account for this since we are transferring power at rotation. I made a quick call to our rep at Boeing and he is going to research and get back to me. (He agreed that the docs should be the same but they aren't... This happens in about 200 places that we know of- and comes from working with different versions of the same machine and documentation- sometimes we have to dig a bit to figure out what the current status of something is...)

 

Whenever we hear back (could be hours... could be weeks...) I'll either confirm we have the code correct or update it for SP2... I'll try to remember to dig this thread up too and let you know what the results were...

As far as I reember it works only at lift off as Robert already said.

 

And I tested it an year ago on the ngx and it was working.

You may be right Andrea. If so the manual is contradictory. Also i was able to find an american airlines cbt i got about 12 years ago and it specifically says if you take off then the apu fails it will auto connect the idg's. It stresses after takeoff and does not mention "at liftoff." This cbt is old so things may have changed. Either way capt Randazzo is on it!

Also my ng knowledge is not fully up to date, and some things are gradually removed from memory, as I don't have manuals on my tablet, I can only check tomorrow. Waiting obviously the official answer from Robert that will clear any doubt.

So wait a minute, I'm confused. Did you have the Engine GEN switches inadvertantly switched OFF or did you have them on with the APU GENs on as well with the APU providing full AC power? That would be a really cool Boeing feature if the engine generators come online automatically in the event of losing APU power after take off even if physically switched off.

 

EDIT: Nevermind. I just read Robert's post about three more times and the associate FCOM entries another three times and now realize that with the Engine GEN switches OFF, the plane will automatically connect the generators if the APU is providing power and it shuts off/fails after takeoff. Very neat little "fail safe" from Boeing.

My NG manuals say nothing about "lift-off," only "in flight."

Ok, I just readed the manual, and the maintenance tells the thing differently but basically tells the same thing of pilot manuals.

I was remembering a lift off, it is only in part true, the manual says "airplane leaves the ground".

So, from what is written the automatic function needs :

 

APU is powering both xfer buses

airplane leaves the ground

APB Opens

Both IDGs are valid (115V 400Hz)

 

So, basically, it will not work untill lift off, then, it waits the APU shutdown or another APU protection that will open APB, then it will switch to the engine generators.

Why it doesn't tell "aircraft in air"?

Probably because this condition will be avaiable onec, only after a take off with apu powering the busses.

This probably will prevent an automatic switch inflight if APU is selected for any other reason (this preventing that the system will ignore what pilot commands).

 

Obviously this is my way of reading the manual, still waiting for official answer.

It's worth taking a step back here, and marveling at the fact that we have such a deep systems simulation that - over a year after release, an oddity appears for the first time, and RSR has to go to BOEING to verify the exact behavior!

 

Not wanting to take us off-topic too far here, but I thought this was a perfect example of what a great 'age' of simming we're in. Just wait until we're all here pondering obscure EFIS messages from our B777 flight decks! ^_^

There is a feature on the 737 NG where the Generator Control Breaker (GCB) closes automatically .

The Generator Control Unit (GCU) sends a close signal to the GCB when these condition occurs;

 

- fire switch is in the normal position

- BTB is open.

- Airplane is in the air mode.

- both GCB's are open on transition to the air mode and the APU is the only power source on the airplane.

- the Auxilary Power Breaker (APB) opens.

 

This occurs only once in flight, This feature gets a reset on transition to the GND mode.

This a quote from the AMM