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Author Topic: Quadruple Generator fail...  (Read 883 times)

RogerH

  • Join date: Dec 2017
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Quadruple Generator fail...
« on: Thu, 12 Sep 2019 16:01 »
Hi all,

There I am, pottering along at FL210 on the way from EGLL to LGIR, prior to climbing further, when I get 4 messages 'ELEC GEN OFF' one for each engine.

Had a good look around, tried recycling the demand pump switches, Gen cont switches and the Bus Tie switches (wish i hadn't done that...). No Joy.

Carefully scrutinised all the breakesr - nothing out.

I evntually restarted the engines one at a time and got the generators running that way. probably not SOP but it worked - and I learnt a lot about rudder trim in the process... :-)

So, obviously not an individual fault in each generator, but something which is common to all.

Suggestions please. Bound to be something simple which i should know.

Cheers,

Roger.

Edit: A kind soul has pointed out I might have been on APU all the time and it flamed out at FL210. Not beyond the realms of possibility. Still learning - and difficult to self-teach something so complicated. Will try it out tomorrow - but it does kinda have an inevitable logic to it!
« Last edit: Thu, 12 Sep 2019 22:11 by RogerH »

Hardy Heinlin

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Re: Quadruple Generator fail...
« Reply #1 on: Fri, 13 Sep 2019 02:05 »
Hi Roger,

to me it sounds like a lightning strike that opened all AC bus breakers.

It should be possible to reset each AC bus: First cycle the GEN switch OFF/ON, then the bus tie OFF/ON. Do this for one bus. Then the next bus.

Cycling the HYD DEM pump switches will not help.

In flight, the APU cannot provide electrical power (just bleed air). If all your electrical power came from the APU alone, you would have lost all power on the ground already after setting takeoff thrust. Takeoff thrust causes the APU GEN breakers to switch from ON to AVAIL -- this is so by design to avoid surprises after liftoff :-)


Cheers,

|-|ardy

RogerH

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Re: Quadruple Generator fail...
« Reply #2 on: Fri, 13 Sep 2019 07:43 »
Thanks Hardy - I’ll try to find a thunderstorm to practice!

jcomm

  • Join date: Dec 2011
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Re: Quadruple Generator fail...
« Reply #3 on: Fri, 13 Sep 2019 10:06 »

RogerH

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Re: Quadruple Generator fail...
« Reply #4 on: Fri, 13 Sep 2019 10:19 »
Don’t you just love this simulator world? A whole website dedicated to finding bad weather!

RogerH

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Re: Quadruple Generator fail...
« Reply #5 on: Sat, 14 Sep 2019 10:29 »
Actually Hardy,

The import of something you said in your post has just hit me - you said the APU breakers go from ON to AVAIL on application of takeoff thrust. I'm not sure if this was the case on takeoff, because I didn't have the OHD in view, but certainly once I looked at the OHD after the warning messages, the APU breakers were showing AVAIL. I assume this is because I must have left the APU running after takeoff - I try to remember to go through the checklists but could easily have failed to do the after takeoff list.

Of course, I tried pushing them to switch them on but given your explanation that was not going to happen! Rotating the APU start switch had no effect either.

So, what was happening to the electrics? Everything was still working - all instruments and displays, presumably hydraulics since the Autopilot was still engaged.

All I got was the four ELEC GEN OFF messages, and the weird indications on the OHD (although they now make sense from your explanation) - but everything still worked fine. Batteries? Capable of running all systems for a time?

In the marine world, we have to have backup batteries on our boats which will maintain full operational capability of essential comms and navigational equipment for a specified period (forgotten what it is but then I've been out of the industry for 8 years) - similar in aviation?

Cheers,

Roger.

Hardy Heinlin

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Re: Quadruple Generator fail...
« Reply #6 on: Sat, 14 Sep 2019 11:40 »
When the APU GENs go from ON to AVAIL, your four engine GENs will automatically connect (if your engines are running). So to get a total power loss, all your engine GEN switches had to be set to OFF. You certainly didn't do this. Otherwise you would've got a total power loss after setting takeoff thrust.

I'm sure you got a lightning strike. When this happens, all AC busses disconnect at once.

The most essential instruments are powered by the battery busses, not by the AC busses directly. You won't die when all AC busses fail. Yes, similar in aviation.


Regards,

|-|ardy
« Last edit: Sat, 14 Sep 2019 12:29 by Hardy Heinlin »

RogerH

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Re: Quadruple Generator fail...
« Reply #7 on: Sat, 14 Sep 2019 12:37 »
Thanks for the education Hardy - one last thing - I understand re. the battery bus running the instruments. I assume same with hyraulic demand pumps - electrically powered still?

Hardy Heinlin

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Re: Quadruple Generator fail...
« Reply #8 on: Sat, 14 Sep 2019 12:59 »
The electric hyraulic demand pumps are powered by the AC busses, never by battery power.

They are not that essential. In flight you have 8 hydraulic pumps, 4 of them (the EDPs) still run when the engines are flamed out and windmilling in flight.


|-|ardy


In the Aerowinx manual, page 213 through 225, are some AC/DC bus equipment lists. All components on these pages are not powered by the batteries (if not indicated otherwise).

RogerH

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Re: Quadruple Generator fail...
« Reply #9 on: Sat, 14 Sep 2019 15:00 »
Thanks for the pointer to the manual pages :-)

Jeroen Hoppenbrouwers

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Re: Quadruple Generator fail...
« Reply #10 on: Sun, 15 Sep 2019 04:54 »
I recently spent way too much time in 777 aircraft and I can relay some tidbits concerning essential system power.

On a 777, many previously separate avionics boxes including the FMCs, the CMU, the CMC etc. have been moved into a common computer array called AIMS. One AIMS "cabinet" is a row of 5 or 6 (I forgot) 1u CPU modules where each unit still has a declared function (on the 787 they went one step further in integration). AIMS contains a lot of important functionality including all flight deck displays, excluding the MCDUs and the standby instrument. So when AIMS goes, you're dark up front.

AIMS has two cabinets. Each cabinet checks up on the other and provides standby redundancy.

AIMS is a computer, so it goes stupid on occasion and yes, you need to reset it. Because this thing does so many really important things, it has multiple power supplies. Four circuit breakers provide each cabinet with AC power, so on the flight deck overhead panel you have eight CBs for AIMS. To reset AIMS, you pull these eight.

But as AC power goes down on interesting events such as a lightning strike, and AIMS is quite needed for flight, it also is fed 28V DC from the Hot Battery Bus, i.e., without any switch or relay in between the battery and AIMS. Except for two circuit breakers that are there to protect the wiring in case of a short-circuit. These breakers are not on the flight deck, but down below in the equipment center. To fully reset AIMS, you therefore have to pull the eight breakers upstairs first, then climb down, pull the two breakers below, count to ten, and then work the other way. It takes three minutes for AIMS to get to the point that the flight deck displays come up again.

After which it finally wants to talk to my SATCOM box again.

All fun.

Hoppie

RogerH

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Re: Quadruple Generator fail...
« Reply #11 on: Sun, 15 Sep 2019 20:40 »
Heh!

You guys _know_ so much!

I'm just glad if i remember to turn on the APU before shutting down the engines, so I avoid losing my OOOI data. I do the checklist, but when it comes to APU Power - that's when I turn it on - thus forgetting to actually connect it later. Should I turn on the APU with the other 'leaving runway' actions, like raising flaps - turn off landing lights - turn off strobes etc.?

Effectively I'm asking 'when does the APU go on after landing?

Britjet

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Re: Quadruple Generator fail...
« Reply #12 on: Mon, 16 Sep 2019 10:34 »
To save fuel, ideally about a minute or so before parking. But don’t put it online until the brakes are set.
Peter.

emerydc8

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Re: Quadruple Generator fail...
« Reply #13 on: Mon, 16 Sep 2019 20:51 »
Quote
Effectively I'm asking 'when does the APU go on after landing?

It's usually part of the FO's after landing flows, and it's on the after landing checklist, so it's kind of hard to miss it twice. It's kind of muscle-memory for the captains to retract the speedbrakes and call "flaps up after landing check" as we exit the runway. I always want the APU started, so the FO usually doesn't have to ask me if I want it -- he just starts it automatically (DHL ground power is that bad).

Jeroen Hoppenbrouwers

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Re: Quadruple Generator fail...
« Reply #14 on: Tue, 17 Sep 2019 00:03 »
Another important thing concerning check lists. Most of these are not to-do lists -- they are CHECK lists. Pilots are assumed to set up stuff at certain moments in the flight, like here, when turning off the runway. The pilot flying (pilot driving now) calls "After landing items" and the other pilot performs these, usually silent. (S)he switches lights, starts the APU, retracts flaps, retracts speed brakes, switches off the weather radar etc. which all is nearly a well-rehearsed choreography if you have done it 100 times before. Also, these are not the same between operators. Some may have task divisions captain/FO, others flying/monitoring, etc. Procedures are suggested by Boeing but not enforced.

Only when the truly critical things MUST have been done, the check list comes out, and if anything appears that isn't right, it either is corrected on the spot ("oops!") or it is prepared and the whole check list is canceled and will be rerun, in its entirety, when the item can be corrected. If you forgot to start the APU when leaving the runway, you will need to cancel the after landing checklist and wait until it has been started and connected, then rerun the checklist.

Assuming of course that your after landing checklist wants you to be on APU power. This can as well be an item on the before shutdown checklist if there is one.

Checklists contain "killer items," but not everything. Procedures are much, much more involved than just checklists, but you don't see them in the movies   :-)

Checklists also are very much scrutinised by the certification authorities.


Hoppie

emerydc8

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Re: Quadruple Generator fail...
« Reply #15 on: Tue, 17 Sep 2019 14:09 »
Quote
If you forgot to start the APU when leaving the runway, you will need to cancel the after landing checklist and wait until it has been started and connected, then rerun the checklist.

Like Peter mentioned, you can hold off on the APU until closer to the gate, but when you finally start the APU, there is no need to re-do the after landing checklist -- at least not in our operation.

RogerH

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Re: Quadruple Generator fail...
« Reply #16 on: Wed, 2 Oct 2019 09:55 »
Thanks for all the input gentlemen.

I used to _start_ the APU during the after landing checklist ("APU electrics" call), but subsequently sometimes (ok - often) forgot to _connect_ it before shutting down the engines or connecting ground power. Thus I lost my lovely OOOI data in ACARS...

So now I start the APU as part of my leaving the runway actions (Lights - Camera - Action!) and _connect_ it when doing the after landing checklist. I completely get Peter's point about fuel - but I think I'm at such a 'rookie' stage that I'll forget about that one for a bit!

All of which leads to a further question:

Is there ever a time when you don't bother with the APU at all? Get to the stand, connect shore power, stop engines in that order?

Thanks,

Roger.




John H Watson

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Re: Quadruple Generator fail...
« Reply #17 on: Thu, 3 Oct 2019 00:19 »
Quote
Is there ever a time when you don't bother with the APU at all? Get to the stand, connect shore power, stop engines in that order?

Rant on: Some airlines have or have had this policy. It's a real pain and helps no one (except justifying a tunnel-visioned bean-counter's existence). It requires additional manpower on the ground (you can't position chocks and plug in power at the same time). It forces the ground crews to rush about, risking injury. Having the engines running longer stops ground traffic passage behind the aircraft and stops service vehicles and personnel approaching the aircraft.

Some ground power sources are attached to the aerobridges and you have to go through an abnormal sequence of fitting ground power before moving the bridge towards the aircraft (Legally, you can't postion the aerobridge until the engines have been shut down). With the power leads running from the aerobridge to the aircraft, you run the risk of running over the leads when you move the aerobridge towards the aircraft.

I've been injured twice fitting external power to an aircraft (the power leads are not light and if suitable steps are not available, you have to lift a heavy weight high above your head).

Rant off.

Hardy Heinlin

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Re: Quadruple Generator fail...
« Reply #18 on: Thu, 3 Oct 2019 01:29 »
Ouch. Did you fall from the steps?

John H Watson

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Re: Quadruple Generator fail...
« Reply #19 on: Thu, 3 Oct 2019 02:28 »
Back and shoulder strain, when steps haven't been available. Steps I'm ok with   ;D

The paperwork is horrendous for this kind of thing.

Of course, the customer airline doesn't get charged for lost time and medical fees, so their bean-counters don't care. The injury rate was so bad, our airline even organised a safety course for aircraft power application. Customer airlines won't get charged for that, either (at least not directly).