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B737ng generator failure abnormal checklist

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B737ng generator failure abnormal checklist

Old 29th Feb 2020, 16:18
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B737ng generator failure abnormal checklist

Hello everyone, my question relates to the proper abnormal checklist to call in the event of a generator failure. Let me offer you the following scenario: you are flying along and all of a sudden the master caution comes on, you as PF call for MC, IDENTIFY, the PNF answers ELECTRICAL, LEFT GEN OFF BUS, SOURCE OFF and DRIVE, you acknowledge and ask for CANCEL MC, I HAVE CONTROLS AND ATC, START APU and COMPLETE DRIVE ABNORMAL CHECKLIST as the failure is on Constant speed drive - low oil pressure - Whereas if you have a generator failure on the generator side without the DRIVE light illuminating - is that even possible? - would you call for the SOURCE OFF abnormal? Basically when do you refer to the SOURCE OFF and when to the DRIVE abnormal checklists? Many thanks everyone for your willingness
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Old 29th Feb 2020, 18:19
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If you apply system knowledge you could say that the DRIVE failure is the cause of the SOURCE OFF annunciation, so it would make sense to go to the DRIVE NNC first. However, nowhere in the QRH does it say that the DRIVE NNC has a higher priority than the SOURCE OFF NNC, so it would not be wrong to look at that one first.

Yes, the SOURCE OFF light can come on without the DRIVE light. SOURCE OFF doesn't mean that the IDG has failed, it only indicates that the last selected source is no longer powering the associated transfer bus. You might or might not be able to select it back on the bus. However, ask yourself why it tripped off in the first place and whether it could happen again.

Ps: unless your company uses a modified version of the QRH there are no memory items associated with either checklist. Either NNC will direct you to start the APU, it is not a memory item.
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Old 29th Feb 2020, 18:26
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I don't have my books with me now, but I remember that during my command upgrade I used the trick of using the highest light on electrical failures, but look if it isn't dual eng fail, or loss of both eng driven gen. Keeps your brain ready for the next thing!
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Old 29th Feb 2020, 21:28
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I was always taught, and now teach, that when you get the Master Caution ELEC that you start from the top of the electrical panel and work down. In doing so whatever light you come to first is the QRH checklist you run. Consequently you would then discover that if the DRIVE light is illuminated, that is the root cause of the ELEC Master Caution, the secondary effect of that malfunction is the SOURCE OFF illuminating. You then ask for the QRH DRIVE checklist and complete that. It is important to do that first as leaving this could cause damage until it is disconnected, start the APU when directed to do so by the QRH. There is no need to complete the SOURCE OFF checklist as this is a secondary effect of the DRIVE malfunction.

Last edited by Johnny [email protected] Pants; 2nd Mar 2020 at 06:47.
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Old 29th Feb 2020, 21:49
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Many thanks for your prompt replies. The logic behind my question is that the QRH for the SOURCE OFF light - together with the GEN OFF light - directs you to attempt a reset first - provided that there is no indication of a short such as smoke or fumes or bus failure but i am diverging now! - while the DRIVE nnc directs you to manually disconnect the idg, which is irreversible in flight, without attempting a reset - which makes sense cos anyway the automation has already disconnected the CSD from the agb, if i am not mistaken. One instructor once told me that if you have the DRIVE light on to carry out the DRIVE checklist first to make sure that you isolate the CSD right away cos if you try to reset the generator the drive portion might overheat and fuse together with the rest of the components of the IDG making it impossible to disconnect it and thus causing a high level of vibrations in the engine - war story that i am just reporting and that according to him took place in a DC9. I was just thinking or maybe overthinking what could make the generating portion of the IDG to fail and the CSD portion still working.
anyway thanks a bunch
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Old 29th Feb 2020, 21:54
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Johnny: Sounds like a sensible way of dealing with it and I cannot see fault in the logic behind it, but I can't remember coming across this in a Boeing manual.

Ps: I think you need to edit that last sentence as it seems you got your checklists mixed up.
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Old 1st Mar 2020, 04:03
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Whenever you get an IDG drop off line, do a quick check to make sure the engine is still running (at or above idle).
While not on 737s, I've lost track of the number of times we saw an engine failure initially diagnosed as an electrical of IDG failure. A few were dual engine events that were initially seen as total electrical power generation failures .
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Old 1st Mar 2020, 13:13
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Originally Posted by tdracer View Post
Whenever you get an IDG drop off line, do a quick check to make sure the engine is still running (at or above idle).
While not on 737s, I've lost track of the number of times we saw an engine failure initially diagnosed as an electrical of IDG failure. A few were dual engine events that were initially seen as total electrical power generation failures .
On our QRH for total electrical failure, (different type) one of the first few lines is "have both engines failed?" I thought it was pretty funny at first, but was then some good food for thought.
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Old 1st Mar 2020, 19:08
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Originally Posted by Vessbot View Post
On our QRH for total electrical failure, (different type) one of the first few lines is "have both engines failed?" I thought it was pretty funny at first, but was then some good food for thought.
Vess, as I noted, it's happened. Boeing added an "ENG FAIL" EICAS message during the development of the 747-400 in large part due to the number of times flight crews had performed troubleshooting of an electrical issue without realizing anengine had quit (777 and 787 have both ENG FAIL - sub idle - and ENG THRUST - thrust is more than 10% away from command and not responding). For reasons I never understood, 'ENG FAIL' logic was added to 767 EICAS, but never enabled .
We had a case roughly 15 years ago - a 767 was descending through Ice Crystal Icing, both engines flamed out (non-FADEC, so no auto-relight, but they had engine anti-ice on which provides continuous ignition). The crew spent several minutes troubleshooting a total electrical failure without realizing the engines were not running . Eventually they exited the Ice Crystals, the engines relite and recovered, while the crew as puzzled as to why the electrical problem went away. It was only after the flight data was downloaded and analyzed that it became apparent the problem was a dual engine flameout.
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Old 2nd Mar 2020, 06:52
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IRRenewal

Ps: I think you need to edit that last sentence as it seems you got your checklists mixed up.
Thanks, it has been duly edited.

You are also correct that the top to bottom diagnosis technique isnít in any Boeing literature, it was a tip that was passed to me and is what I use and teach, itís simple and it works.
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