Nsfguy From , joined Dec 1969, posts, RR: Posted (11 years 2 weeks 2 days 21 hours ago) and read 4679 times:
I was on a NWA 747 NRT-LAX in Oct. And as we were pushing back and starting up in the rain, I noticed something just did not sound right, (42 years flying and you get a feel for this stuff) sure enough the Capt. Announced something like this "folks, as we were starting one of the engines, the gen did not come up just right, SO we are getting a tow back to the gate .... And it won't take long to have a look and get on our way..." We were there about 30 min and the Capt. Announced all is well and we are just waiting for some paperwork to make it all legal and proper, and we'll be in the air soon. I was in the upper deck and heard the three Japanese tech's bolting up the stairs like a stampede and bang on the cockpit door... While the NWA head F/A was yelling "you can't do that! I have to call him on the intercom first!" but he opened the door and the three entered and I guess got the papers in order, then away we went! I know nothing about tech issues, but I have been wondering what in the hell was that all about? I know planes have APU's but generators? And can be fixed in a few min? Geez! Please help me out guys.
B6FA4ever From United States of America, joined Aug 2003, 821 posts, RR: 9
Reply 1, posted (11 years 2 weeks 2 days 21 hours ago) and read 4622 times:
that happened to me too (somewhat). i was flying a UA B747-200 from KIX-HNL back in '95 and we had an engine problem at push back and then got towed back to the gate for about 30 min or so. but the capt said there was just a little mechanical issue that can be taken care of really quick.
the generator ur capt was talking about was probably the engine he was talking about...but i could be wrong
Asgeirs From Iceland, joined May 2001, 518 posts, RR: 1
Reply 2, posted (11 years 2 weeks 2 days 20 hours ago) and read 4556 times:
He might have been talking about the electricity generator connected to the engine. Those generators provide all the electricity used by the aircraft while in flight. The APU's are only used while on the ground with the main engines shut down.
The generator probably wasn't delivering acceptable current or something. Could be something the can fix quickly.
Reykjavik Aviation Photography - Just bring the aircraft to us and we'll photograph them! :-)
MD88Captain From United States of America, joined Nov 2001, 1351 posts, RR: 19
Reply 3, posted (11 years 2 weeks 2 days 17 hours ago) and read 4281 times:
Each engine turns a generator which in turn provides all the electricity for the aircraft. After engine start the engine generator on that engine probably did not function correctly so the aricraft returned to the gate. The generator probably wasn't fixed before you departed, but certain paperwork deferring the maintenance had to be filled out. You can legally depart without a generator on almost all airliners. There are very strict procedures for when maintenance can be deferred (especially on international flights). It sounds like a typical day at the office. I'm sure everthing was done just exactly as it should be done.
AlitaliaMD11 From Spain, joined Dec 2003, 4068 posts, RR: 13
Reply 5, posted (11 years 2 weeks 2 days 15 hours ago) and read 4067 times:
maybe he did not want the passengers to worry, so he said generator instead of enigne.
This reminds me of the last episode of Friends and when Rachel is on the plane and her friend pheobe calls her and tells her theres something wrong with the left "Falangee" and Rachels seat partner gets nervous and wants to get out of the plance, so they have to delay the plane becuase there is something wrong with the left Falangee! And of course Rachel knew there was nothing called a Falangee.
IFIXCF6 From United States of America, joined Sep 2004, 108 posts, RR: 0
Reply 7, posted (11 years 2 weeks 2 days 13 hours ago) and read 3832 times:
Just a possibility...
If the techs had done any maintenance requiring an IDG (generator) disconnection, done from the flight deck, and forgotten to reset it, done only at the engine, that could explain it. I have seen it happen.
HAWK21M From India, joined Jan 2001, 31851 posts, RR: 54
Reply 9, posted (11 years 2 weeks 2 days 9 hours ago) and read 3620 times:
Either the Generator of that side Engine was deffered under MEL.
On a B732 we've had a delay of a few minutes after the Pilot reported following Engine Startup that the CSD LOP lt was not Extinguished,so no Gen Available.After shutdown,the CSD disconnect was reset & Start up carried out satisfactory.
I wonder if the B747 has a CSD disconnect.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 11, posted (11 years 2 weeks 2 days ago) and read 3554 times:
Here's the dirt on the B747 (classic) electrical system. There are 4 generators installed (1 each engine). In a normally operating system all 4 generators are powering the aircraft, they are in parallel. At no time (normal ops) does one (or 2 or 3) generator power the aircraft. (except certain conditions during start-up).
If one fails to come on-line or fails to give the proper output, its CSD (constant speed drive) needs to be dis-connected. This is accomplished from the cockpit. The remaining generators will pick up the inop generator's buss and once again operate in parallel.
It sounds to me like a generating system failure at start-up (I don't know how you would hear that) but if the one of the systems failed, the flight crew would dis-connect and since still in the terminal area (depends on airline) may have needed to get the paperwork squared away.
Now I don't know much about the B744, but I would imagine it was much like the B757/B767. Those generators run isolated and power their own respective busses. Only during a failure (or start-up/shut-down) will one generator power another's buss. Also, I believe IDG's (integral drive generators) are used. They are still disconnected from the flight deck.
I could be wrong on the B744, never worked it or even seen the cockpit in detail.
[Edited 2005-01-28 15:14:58]
Just found a picture of the B744 overhead. It appears to me that the generators do run isolated as normal ops.
Dl757md From United States of America, joined May 2004, 1563 posts, RR: 14
Reply 16, posted (11 years 2 weeks 1 day 2 hours ago) and read 3402 times:
They are located on the accessory gearbox which is mechanically driven by the N2 rotor via the tower shaft. The gearbox is mounted on either the bottom or side of the engine and the generator is attached to Constant Speed Drive(CSD) which in turn is attached to a mounting pad on the gearbox.
The CSD is basically a self contained hydraulic pump/motor combination that delivers a constant RPM output over all normal engine operating or input RPM.
An Integrated Drive Generator or IDG is a single unit that contains a generator and CSD.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 19, posted (11 years 2 weeks 22 hours ago) and read 3375 times:
From the DC8 AMM (the only one we have on computer that has a CSD installed):
A constant speed drive (CSD) transmission is installed on each engine to provide a means of driving an AC generator at a constant speed regardless of variations in engine operating speeds and applied electrical loads. The transmission is located on the forward section of the engine accessory drive case, at the lower centerline of the engine. A quick attach-detach (QAD) kit is used to secure the transmission to the engine accessory drive case.
The CSD and IDG are transmissions. They take an input and modify it into a usable output (in this case a constant RPM, regardless of input speed).