lmml 14/32
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B733 Looses No1 Generator And APU Inflight

Wed Aug 03, 2005 8:03 pm

Yesterday, we had to return to base after the number 2 generator failed and the APU quit minutes after it was started at FL340. How serious is such a situation? What did the B733 lose in this case? Would the APU and the number 1 generator have sustained normal flight for 3 hours? If so what are the flight limitations?
 
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HAWK21M
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RE: B733 Looses No1 Generator And APU Inflight

Wed Aug 03, 2005 8:13 pm

Quoting LMML 14/32 (Thread starter):
Would the APU and the number 1 generator have sustained normal flight for 3 hours

Def APU & #1 Gen should have been adequate.
It happened here once on S2 B732 long time ago.

How was the APU track record prior to this flt.
What was the Reason for #2 Gen u/s.What Indication.

regds
MEL
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MD11Engineer
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RE: B733 Looses No1 Generator And APU Inflight

Wed Aug 03, 2005 11:31 pm

While one generator can power the plane's systems (minus the cabin bus with the high power consumption galleys) through the transfer busses, there would have been virtually no redundancy left. The only redundancy in case of the last generator packing up would have been the ship's battery, which can provide emergency power to the standby instruments for about 20 minutes.

Jan
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kaddyuk
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RE: B733 Looses No1 Generator And APU Inflight

Wed Aug 03, 2005 11:32 pm

Quoting LMML 14/32 (Thread starter):
What did the B733 lose in this case? Would the APU and the number 1 generator have sustained normal flight for 3 hours? If so what are the flight limitations?

I would imagine that the crew would have started to load shed the bus bars.

IFE, Ovens, Boilers, fridges etc will be switched off. I think secondary radios and non-essential items would loose the juice. If they loose too much then that causes the divert.
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SlamClick
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RE: B733 Looses No1 Generator And APU Inflight

Wed Aug 03, 2005 11:39 pm

Had to disconnect a generator drive once on a 737. Started the APU first, then turned off the bad generator and disconnected it. That happened over New York State and we flew all the way to the west coast on two gens. Not a problem at all except that we had lost our redundancy. Had the APU quit at some point we'd have had a whole new situation.

Turned out the CSD was just low on oil. Temperature was high, rise was high and when the frequency started to fluctuate it was time to cage it.
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cdfmxtech
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RE: B733 Looses No1 Generator And APU Inflight

Thu Aug 04, 2005 2:10 pm

The 737 Classics would lose everything on the opposite side Generator Bus, which in turn powers the main Bus.
In this case, the No.2 side Gen & Main Busses would have been unpowered.

Here is what you lose:

No. 2 Tank Forward Fuel Pump
Center Tank Left Fuel Pump
Fuel Temperature Indicator
Galley(s) Inoperative
Generator Bus No. 2
TR Unit No. 3
Equipment Cooling - Alternate If Switch is to Alternate
Left Side Window Heat
Right Forward Window Heat
Right No. 4 & No. 5 Window Heat
Right Elevator Pitot Heat
Temp Probe Heat
Recirculating Fan
RIGHT OUTBOARD LANDING Light
LEFT INBOARD LANDING Light
RIGHT RUNWAY TURN Light
Engine Vibration Amplifier
 
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IFixPlanes
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RE: B733 Looses No Generator And APU Inflight

Thu Aug 04, 2005 6:21 pm

If you have only IDG 1 left, the "LOAD SHED RELAYS" correlating to the "AC XFR BUS 2" open.



Ingo
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MD11Engineer
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RE: B733 Looses No1 Generator And APU Inflight

Thu Aug 04, 2005 8:16 pm

What do you think you have the two bus tie breakers for (BTB1 and BTB2)?
They can close them and connect the left transfer bus to the right transfer bus. 90kW of power are quite enough, especially since the galley busses will be automatically shed, leaving all power for the aircraft systems. This will mean no light in the cabin, no galley power (except for the emergency lights) and no working toilets, but you can live without it. The plane was designed that, while normally each generator would feed it's own half of the plane (therefore eliminating the problems going with synchronising AC generators), in necessary each generator ca power the whole plane. E.g. the APU generator is doing exactly this on the ground and it is not bigger than the engine generators.
One generator is enough to power the systems, you just don't have ANY redundancy left. Should the last generator pack in, then you'll be down to the battery, dark cockpit and standby instruments for 20-30 minutes.

Jan

[Edited 2005-08-04 13:26:29]
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cdfmxtech
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RE: B733 Looses No1 Generator And APU Inflight

Fri Aug 05, 2005 5:09 am

MD11Engineer and Ifixplanes

The poster asked about 737-300s, which are only 45kva per generator.
 
MD11Engineer
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RE: B733 Looses No1 Generator And APU Inflight

Fri Aug 05, 2005 6:15 am

45 kW should still be able to power the whole aircraft, without the high current consumers galley ovens and coffee makers. If necessary you might have shut down one of the electric hydraulic pumps temporarely (during cruise, switch it on during approach again). The whole 737 electric system has been designed to have some redundancy.
Even then, with 2/3 of my generating capacity off, as a pilot, I would be looking for the next airport for an emergency landing.

Jan
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Buzz
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RE: B733 Looses No1 Generator And APU Inflight

Sun Aug 07, 2005 9:33 pm

Hi LMML 14/32, Buzz here. MD11 Engineer pointed out that you can get along and fly with a single generator.
But many pilots get to thinking... what's the next bad thing that will happen to me? So if you lose that last generator you really have to work to find an airport (night? fog? rain and wind?) and get that sick airplane on a runway. It's not quite like flying a Cub or a Champ with the windows open on a nice day.
g'day
 
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RE: B733 Looses No1 Generator And APU Inflight

Sun Aug 07, 2005 9:59 pm

Obviously, when you are down to one generator, you should start looking for the next available airport. You are not yet in a direct emergency situation, but you have lost all redundancy, so, if the last generator packs in, you will be up sh*t creek without a paddle.

Jan
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lmml 14/32
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RE: B733 Looses No1 Generator And APU Inflight

Mon Aug 08, 2005 3:10 am

Thank you all for your replies. Put your mind at rest. We returned to base and were on the ground in 20 minutes. The generator was replaced and we were on our way again in no time - minus 4 passengers who decided that one scare was enough for one day.
 
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HAWK21M
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RE: B733 Looses No1 Generator And APU Inflight

Mon Aug 08, 2005 2:24 pm

Quoting LMML 14/32 (Reply 12):

What was done about the APU.
regds
MEL
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Bjones
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RE: B733 Looses No1 Generator And APU Inflight

Mon Aug 08, 2005 2:52 pm

The 737 can be operated with either one engine generator inop or the APU (or APU generator) inop. In either case as long as it is properly MELd then you can operate a revenue flight. With one engine driven generator inop there is a fuel burn penalty because you must fly with the APU running.

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