737NG's questions

[N1 Limit]

Hey guys

I've got some doubts about this question on electrcity check it out


In flight, if the APU is supplying both AC Transfer busses, positioning the BUS TRANS switch to OFF will:

1) Cause AC Transfer bus No.1 to lose power
2) Cause AC Transfer bus No.2 to lose power

3) Cause both AC Transfer busses to lose power
4) Not cause either AC Transfer bus to fail.
For this the answer should be 3 but smartcockpit says 2 is the answer.anybody out there to help me resolve this ambiguity?

Here goes another one:

Why when you loose AC transfert Bus 1 and DC Bus 1 the battery/battery charger immediately power AC stby and DC stby Bus whereas in case you lost DC Bus 1 TRE through the cross bus tie relay can power DC stby Bus?Many thanks

[Artisan]

There are two basic principles of operation for the 737 electrical system:
• There is no paralleling of the AC sources of power.
• The source of power being connected to a transfer bus automatically
disconnects an existing source.

BUS TRANSFER Switch
AUTO (guarded position) – BTBs operate automatically to maintain power to AC
transfer busses from any operating generator or external power
• DC cross tie relay automatically provides normal or isolated operation as
required.
OFF – isolates AC transfer bus 1 from AC transfer bus 2 if one IDG is supplying
power to both AC transfer busses
• DC cross tie relay opens to isolate DC bus 1 from DC bus 2.
OFF- causes both BTB's to open, isolating the transfer busses. APU power is supplied to the tranfer busses via the BTB's. If the BTB's are open, no APU power is supplied to any transfer bus.
If IDG1 was powering both Transfer busses and the BUS TRANSFER Switch was selected off, then Tranfer bus1 would remain powered, while TB2 would lose power.

[N1 Limit]

Thanks Artisan for the feedback
So why when you loose let's say IDG1 with Bus Transfert ON you've got SOURCE OFF from the failed side?Since the BTB close and power AC transfert Bus 1 from IDG 2 it's a SOURCE!!!

[STBYRUD]

Yes and no. SOURCE OFF just indicates, as stated in the manual, that the last manually selected source has dropped off but says nothing about the state of the transfer bus, thats what the TRANSFER BUS OFF light is for. In flight, if you just get a SOURCE OFF light, the IDG has most likely failed on that side.

[N1 Limit]

Hey Guys
can we debate on this question below,i chose the 3rd answer which is PTU but it says it's Electrical Motor rather,why?


With the loss of the system B hydraulic fluid and the system B FLIGHT CONTROL switch to STBY RUD, what allows the movement of trailing edge flaps?

[/URL] A system pressure.
(http://www.pprune.org/#) Standby hydraulic system pressure.
Power Transfer Unit (PTU).
[URL="http://www.pprune.org/#"] (http://www.pprune.org/#) Electrical motor

[N1 Limit]

Hey Guys
can we debate on this question below,i chose the 3rd answer which is PTU but it says it's Electrical Motor rather,why?


With the loss of the system B hydraulic fluid and the system B FLIGHT CONTROL switch to STBY RUD, what allows the movement of trailing edge flaps?

[/URL] A system pressure.
(http://www.pprune.org/#) Standby hydraulic system pressure.
Power Transfer Unit (PTU).
[URL="http://www.pprune.org/#"] (http://www.pprune.org/#) Electrical motor

[N1 Limit]

How about this one?

The amber FEEL DIFF PRESS light illuminates when the:

[/URL] Flaps are up & a pressure imbalance between hydraulic systems A & B is detected or if one of the elevator feel pitot systems fails
(http://www.pprune.org/#) Flaps are not up and a hydraulic pressure imbalance is detected
or one of the elevator feel pitot systems fails
Flaps are up or down and a hydraulic pressure imbalance is detected or if one of the elevator pitot systems fails.
[URL="http://www.pprune.org/#"] (http://www.pprune.org/#) No correct answer is provided

[STBYRUD]

Depends on the date of manufacture of the particular ship. The older NGs inhibit FEEL DIFF PRESS if flaps are not up, it is always available on the newer ones. could mean that the actual feel computer has failed, that its inputs (the elevator pitots) have failed or that the hydraulic pressure differential exceeded 25% for more than 30 seconds.

Oh, and there is more to say about the PTU: Its supposed to aid the (very weak) electric B pump in extending and retracting the LED and more importantly ensures rapid autoslat operation to prevent an imminent stall, even if normal sys B quantity has been lost (since it retains some liquid) until the first deployment.

[Avenger]

N1 Limit, do you have the systems manual or are you only trying to cross check answers, I am confused, if you have the manuals, you have the answers,,l