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rondon9898

Systems redundancy and diversion

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Hi chaps,

 

On a flight from EGLL-CYYZ the other day I got a BREAKER message on the EICAS status and the left generator went off. I followed the QRH procedure, which was essentially to switch the GEN off and on again and I'm aware in aviation that the policy for electrical items is to only attempt them once (though in the little Cessna that I fly, my instructor says that if a CB pops you shouldn't try and reset it unless it's absolutely vital to flight safety, and in a Cessna there's very little on board that ticks that box). The GEN remained off, so the next step was to start the APU. My question is this: should I have diverted? I was about three quarters the way across the atlantic at this stage and landed with plenty of fuel on board, despite running the APU for the remainder of the flight. However, given that one generator could be considered failed, how much redundancy can you rely on before diversion is necessary? Would it have been acceptable in real life to just carry on the flight with the APU running? I've had one or two malfunctions in teh PMDG 777 like this before and although I enjoy solving the problems and following the correct EICAS/QRH procedures, I never quite know when to divert or when to carry on. 

 

Cheers chaps,

 

John

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I love that route.  The decision to divert or not depends on the airline's SOP - IIRC, the only "definitive" diversions are the ones that say "land as soon as possible" in the QRH.  Since we (usually) don't have the current airline's SOP, the decision is, like in the sky, the captain's to make.  In that case, you were the captain, you decided to carry on, and landed safely at your destination.  The passengers wouldn't even have noticed it.  Good job!

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A BA744 lost an engine on takeoff at KLAX and proceeded to EGLL... about two years ago? I recall they did have to divert early for fuel at maybe Shannon, don't recall exactly.  The pilot was criticized by some but BA backed him and he didn't even bend any rules.

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A good rule of thumb is to divert when you no longer have redudancy on primary systems (hydraulics/electrics/navigational equipment/etc)

 

So with 3 hydraulical systems, if 2 systems fail....divert.

With 2 engines, if one fails.....divert.

With 3 Generators (L,R and APU).....if one fails continue...if 2 fail divert.

I know an arguement could be made that you also still have backup generators and a Battery.

 

But that why is call it a good rule of thumb.....open for discussion.

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It is one of those situations where as the commander you have to weigh up the options and make the call.

 

ETOPS requires "multiple sources" of electical power (for dispatch) and in order to gain ETOPS approval most (if not all) twins are required to be able to start the APU in flight to act as a backup generator in exactly the situation you describe (compare to the 747-400 APU, for instance, which cannot be started in flight).

 

As Max says, if the QRH doesn't say Land ASAP, it's up to you to weigh up the options. You could start with a TDODAR:

 

Time -- is the situation time-critical? Is the aircraft going to fall out of the sky if we don't act now? In this case, no. There's plenty of fuel, the aircraft is quite happily on its route and flying very nicely. So we can take our time in making a decision.

Diagnosis: What's gone wrong? Do we know why it's gone wrong? Is it something that could affect other systems or cascade in to further failures -- or is there the danger of a common fault that could affect the redundant systems?

Options: What can we do? Essentially: divert, return to LHR, continue to destination. Return to LHR is almost certainly out if we're 3/4 of the way across the Atlantic: we won't have enough fuel. So the remaining options are divert or continue to destination. Where could we divert to? What is the weather like? What will happen if we land there -- is there engineering support to fix the problem? What about the pax? How about continuing to destination -- what's the weather like there? Is our Autoland status affected? What about the return sector? At the very least, there will be engineering support, the pax will be where they want to be and there will be airline staff on hand to deal with them.

Decide: Weighing up the options, on the face of it (without knowing the full situation) I would say your decision to continue was probably a good one. The aircraft is flyable, there's no LAND ASAP in the QRH, we have backup electrical power from the APU. There's engineering support there to get the problem fixed and the pax will be dealt with also. Compare that to diverting in to an unfamiliar airfield with little or no facilities for either the aircraft or the pax.

Act/Assign duties: As it says!

Review: We've made our decision, but we need to continually review it. For instance, another failure might alter things: we need to remain flexible to respond to any change in the situation.

 

In your case, you were well on your way to your destination when the fault occurred. Now, to make things interesting: how about if the fault had occurred shortly after TOC ex LHR, or even at, say, just prior to 20W? Would your decision to continue have been the same?

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Excellent answer as usual Simon and to answer your last question, I think Rob's rule of thumb is pretty good actually. Even after TOC or even just after takeoff, would it be worth diverting or going back to EGLL, taking all the passengers off, getting a replacement, cancelling the flight or any of those troublesome things (if we're to treat the sim like a real passenger service) for a lost gen, when I still had 1 functioning and the APU? on reflection i'd say there's more than enough redundancy there. I shall use that rule of thumb for service based failures in the future.

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Even after TOC or even just after takeoff, would it be worth diverting or going back to EGLL, taking all the passengers off, getting a replacement, cancelling the flight or any of those troublesome things (if we're to treat the sim like a real passenger service) for a lost gen, when I still had 1 functioning and the APU? on reflection i'd say there's more than enough redundancy there.

Fair enough! I asked because it's an interesting situation: continue 3000NM with a fault that would cause a diversion/the aircraft to be grounded in YYZ (or worse, YQX/KEF etc) if there's a further failure, vs return to main base where there is full engineering support and almost certainly a replacement aircraft/standby crew (if necessary).

 

It's one of those situations where actually you don't have all the support in the sim that you would in the real world -- in real life you'd be on the blower to Maintrol for an engineering assessment of the situation that could feed in to your decision making.

 

There's no right or wrong answer: I think you'd be absolutely justified in continuing for the reasons you outline. Having said that, based on previous situations I suspect that in practice in reality the engineers would probably ask for the aircraft to return to LHR if the fault occurred early in the flight, though of course the final decision rests with the commander.

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Excellent answer as usual Simon and to answer your last question, I think Rob's rule of thumb is pretty good actually. Even after TOC or even just after takeoff, would it be worth diverting or going back to EGLL, taking all the passengers off, getting a replacement, cancelling the flight or any of those troublesome things (if we're to treat the sim like a real passenger service) for a lost gen, when I still had 1 functioning and the APU? on reflection i'd say there's more than enough redundancy there. I shall use that rule of thumb for service based failures in the future.

 

Another way to look at it - the 777 is able to dispatch with one GEN inoperative if the APU is kept running all flight. (Did I get that terminology right?) I believe this is even true of the 737. So if it can dispatch with pax with this failure, then having the failure occur in flight further backs up your decision to continue.

 

In your example of the failure just after departure, don't forget the fuel you will have to jettison as well...

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That's interesting I don't think i would dispatch the aircraft with a broken generator, even though the MEL says you can. But as Wes says, it certainly suggests that continuing with the failure in flight certainly wasn't the most disastrous thing I could have done.

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That's interesting I don't think i would dispatch the aircraft with a broken generator, even though the MEL says you can. But as Wes says, it certainly suggests that continuing with the failure in flight certainly wasn't the most disastrous thing I could have done.

 

One thing you always need to keep in mind with aviation is that, when you're away from "home," you're generally in a land of higher prices. Say I'm BAW and I operate way too many aircraft out of an airport that can't quite keep up with it anymore. When I'm away from that lovely airport, and in, say, Joburg, I don't have all of the agreements that I have at home, which means everything is going to cost quite a bit more.

  • At home, I fuel hundreds of airplanes, so I can buy fuel at a set rate in bulk; in Joburg, I buy fuel at the daily rate (or even at a negotiated rate, but still likely higher given the lower amounts purchased). See: Tankering
  • At home, I have a maintenance base staffed by my own, or contracted employees (again, negotiated rate), and I'm the first priority; in Joburg, I'd have to settle for whatever rate they charge external clients, and they'd likely put me in line behind any SAA planes.
  • At home, I don't need to worry about downing a plane for something borderline because there's likely a swap somewhere on the field; in Joburg, I'd have to wait for the next arrival 2 hours later, but my passengers on the first departure would get bumped to the second, and would sit space available, which means I'd be paying for hotels for the rest until I can get a "rescue" flight down there, which would probably amount to a 388 swap for the 744 flight (so two 388 flights down for a couple days to recoup), potentially food, and definitely transportation to some degree.

So...pay a metric jackton of money, delay a ton of passenger, and spend a while trying to recover; or fly a plane with a busted engine GEN, but still on two GENs with the APU running? This is one of those things that - even with VAs (I don't recall any who sim MELd items) - a lot of simmers aren't really exposed to. It's understandable, but somewhat unfortunate, because it would probably add some good variation to the usual LNAV/VNAV timebuilding.

 

PS: The poke at EGLL was meant to be a joke. Some of our airports are a lot worse...like Sewark...

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Speaking of APU, my understanding is that if you a flying an ETOPS flight with something like the 737, over, say, the atlantic, you need to turn on the APU on the ground and keep it running all flight incase you lose a gen.

 

I wasn't sure if this was true on the 777 though

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Speaking of APU, my understanding is that if you a flying an ETOPS flight with something like the 737, over, say, the atlantic, you need to turn on the APU on the ground and keep it running all flight incase you lose a gen.

 

I wasn't sure if this was true on the 777 though

 

73, yes. 777, no. The latter has a RAT when things really get ugly.

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So...pay a metric jackton of money, delay a ton of passenger, and spend a while trying to recover; or fly a plane with a busted engine GEN, but still on two GENs with the APU running? This is one of those things that - even with VAs (I don't recall any who sim MELd items) - a lot of simmers aren't really exposed to. It's understandable, but somewhat unfortunate, because it would probably add some good variation to the usual LNAV/VNAV timebuilding.

 

Indeed! However, as I say the bits which will likely always be missing are the conversations with network control/Maintrol etc that would feed in to a decision to go/change aircraft/RTB. Plus, of course, in the sim there's always an engineer on hand who can fix any problem instantly and with a 100% success rate!

 

(incidentally: at our place we do now have a small piece of software which enables panel states (and thus accumulated hours, service-based failures and defects from the previous flight) to be shared between pilots, so there's one!).

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I like the BAWare software, it works really well. I wonder if the owner would lend rm it out to other VA's?

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I'd like a reference for that assertion that a B737 need APU running for ETOPS operation.  I am aware that backup battery checks and crossfeed fuel checks are required but I've been on a B737-700 flight KSNA-PHOG and do not recall the sound of the APU.  Thanks.

 

EDIT:  I found that it is an operator-defined requirement, not regulatory, as long as dispatch and reliability criteria are satisfied.  That matches my experience. Disregard.

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That's interesting I don't think i would dispatch the aircraft with a broken generator, even though the MEL says you can.
You would be quite surprised at the amount of equipment that can be inoperative and the flight still dispatched...

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A gen failure would probably only reduce your ETOPS allowance, from say 180 minutes to 120- which means most flights are still doable. You'd have to work with dispatch to plan a different route (if necessary) and do a fuel re-evaluation.

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