A mixed bag, I know, because I was 'playing' with the NG on the ground this evening rather than flying, and noticed some anomalies. I'd appreciate any comments you might have.1a. With wing fuel pumps off, and center fuel pumps on, fuel is drawn correctly from the center tanks, but if ALL pump are off, the fuel is drawn from the wing tanks, and not by gravity feed from the center tank. That's not right, is it?1b. If I move the start levers Cutoff->Idle and back(to ensure they're actually at cutoff), the Engine and Spar Valve lights stay illuminated brightly until after engine start. Is this correct?2. I am unable to get duct pressure above 15PSI, irrespective of the air source. On the APU, for example, both indicators reach max 15PSI with the following configuration: Both Packs AUTO, Isolation Valve OPEN, ReCirc Fan ON. Probably doing something wrong?3a. Is it possible to show TCAS traffic on the ND without the concentric rings(the TFC knob is dual purpose)? Only way I can do this presently is by using a Centered Display.3b. Are RAs inhibited on the ground? With XPDR switch at TA/RA, the display message is TA ONLY.Looking forward to hearing your replies,Best wishes,Frank

>1a. With wing fuel pumps off, and center fuel pumps on, fuel>is drawn correctly from the center tanks, but if ALL pump are>off, the fuel is drawn from the wing tanks, and not by gravity>feed from the center tank. That's not right, is it?Not sure, but:since engines are on the wings, which in turn have a slight angle upward, the gravity won't ever push fuel from the center tanks (that are below the engines) to the engines... rather from the wings...>2. I am unable to get duct pressure above 15PSI, irrespective>of the air source. On the APU, for example, both indicators>reach max 15PSI with the following configuration: Both Packs>AUTO, Isolation Valve OPEN, ReCirc Fan ON. Probably doing>something wrong?There is indeed a bug in the representation of actual pressure.I do not know the exact behaviour of this bug, other can add details.>3a. Is it possible to show TCAS traffic on the ND without the>concentric rings(the TFC knob is dual purpose)? Only way I can>do this presently is by using a Centered Display.Not that i know.>3b. Are RAs inhibited on the ground? With XPDR switch at>TA/RA, the display message is TA ONLY.RA is inhibited below a certain altitude i don't remember.

>3b. Are RAs inhibited on the ground? With XPDR switch at TA/RA, the display message is TA ONLY.RA is inhibited up to about 1000ft radio altitude and the TA indication should be replaced by TFC.

3a.)http://forums.avsim.net/user_files/95122.jpgHope it helps,

Indeed it does, Mats! I kinda guessed there might be something, as the rings can obscure some detail, but I forgot the menu options(this after looking in the menu system this evening to check color changes for another post!) :-)Many thanks,Frank

Thank you, Claudio.What you say about the fuel system makes sense, but I'm sure I read somewhere about gravity feed from the center tanks. At least, the low pressure lights do not illuminate when the tanks are switched off, which may indicate that they can supply fuel in this configuration?Maybe someone else will comment?By the way, Mats has provided the answer to 3a.BR,Frank

Thanks, George. The ND shows TA ONLY in blue when I am on the ground with transponder in TA/RA.Best wishes,Frank

What you say about the fuel system makes sense, but I'm sure I read somewhere about gravity feed from the center tanks. At least, the low pressure lights do not illuminate when the tanks are switched off, which may indicate that they can supply fuel in this configuration?Maybe someone else will comment?There is no suction feed from the Center Tank, BR. The fuel would have to force its way past the center tank pump internals to get to the engines (not unheard of in aviation, depending on the type of pumps fitted to your aircraft). However, the 737NG wing tanks have special bypass systems (pipes and valves) which bypass the fuel pumps, so you can suck fuel directly out of the tanks. Basically, the fuel takes the path of least resistance.Hope this helps.Cheers.Ian.

Ah, Ian, "suction feed" was the phrase I couldn't think of!Do you know how the suction is provided(do the engines suck? :-)).I'm still trying to remember why the low pressure lights on the center tanks don't illuminate?Thanks very much for the info. It all helps!BR,Frank

>I'm still trying to remember why the low pressure lights on>the center tanks don't illuminate?Sometime ago, i asked this question too (together with some doubts about the fuel system)Saying that maybe there was (is) a bug.The discussion with Randy, degenerated into a debate about the fact that PMDG 737ng is not a professional simulation, and so some imperfections are to be expected.

Gents,1a:With all fuel pumps OFF and engines running the engine driven pumps suck hard enough to supply fuel up to mid20K'.. this is why in QRH when a pump fails you may have to descend because engines may flame out due low fuel pressure.BTW:The low fuel pressure lights are only armed when teh pump swith is tuned on.1b:Will check my books but generally:Bright Blue means the valve is not in the commanded position ie.. in transit or stuck somewhere other than where it should be2In NG the APU Duct prerssure is regulated on demand.. ie when starting engines the APU Duct Pressure goes up but I am not sure what it should go to. Ceratinly in normal operations on ground with APU suppling bleed air to packs 15PSI is about right from memory.3a and 3b answered by others already.Hope this helps folks,

Hi Brad,>1a:>With all fuel pumps OFF and engines running the engine driven>pumps suck hard enough to supply fuel up to mid20K'.. this is>why in QRH when a pump fails you may have to descend because>engines may flame out due low fuel pressure.>BTW:>The low fuel pressure lights are only armed when teh pump>swith is tuned on.Very interesting! Does that mean the fuel pumps I've been referring to are, in fact, the electrically driven boost pumps? Are there also a set of mechanically driven engine pumps?>1b:>Will check my books but generally:>Bright Blue means the valve is not in the commanded position>ie.. in transit or stuck somewhere other than where it should>beYes, that's what I thought. It works fine if you start with the fuel levers at cutoff(lights are dim), but lights go bright and stay bright when you move levers to idle and back to cutoff.>2>In NG the APU Duct prerssure is regulated on demand.. ie when>starting engines the APU Duct Pressure goes up but I am not>sure what it should go to. Ceratinly in normal operations on>ground with APU suppling bleed air to packs 15PSI is about>right from memory.Thanks, Brad. According to flight manual pressure should be 20-25PSI,but I forget if I had the APU supplying air, as well. I guess dual bleed is okay as long as throttle remains in idle?Great to have your advice,BR,Frank