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PSEU 737NG

Old 4th Apr 2012, 14:17
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PSEU 737NG

Hi guys,

I was just wondering, if someone could tell me what the PSEU does and how it operates in detail, because the FCOM does not say much about this system. Friend of mine got PSEU light on the ground recently and was forced to unload the pax and taxi with the empty Boeing around the airport changing configuration and trim until the light extinguished. What I have heard is that you should reset it in E and E compartment but pilots are forbidden to carry out this reset.
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Old 4th Apr 2012, 16:30
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Mainly the PSEU (Proximity Switch Electronics Unit) process the signals from proximity switches (landing gear, doors ...) and send them to several systems.
Taxiing around changing the configuration is not the procedure to clear the PSEU Lt.
The PSEU gives you a fault code. Maintenance manuals tell the next steps...
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Old 4th Apr 2012, 16:33
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That said - if you are stuck at an outstation without MX, its worth trimming full nose down, full up and back to five (no need to offload anyone or taxi around) - this can reset the light in certain cases. Nevertheless something is probably fishy with the system in that case and it should be checked asap.
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Old 4th Apr 2012, 16:54
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Even away from home station a pilot should be able to open the door to the forward equipment compartment and read out the fault at the PSEU (with help from his trouble shooting department via handy, if needed).
I think this would be the safer and (depending on the fault) quicker way.
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Old 4th Apr 2012, 16:58
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Well, thats what maintenance wanted us to do the last time this happened, they wouldn't trust us with opening (or more critically closing) the EE hatch...
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Old 4th Apr 2012, 18:00
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Boeing suggest the trimming when you have the fault code 31-52004 (STAB TRM DISAGREE) because you may have a nuisance fault.
But if you do not look for the fault code, you can not be sure that you really fixed the problem.
I am a little bit concerned, that TS does not think you are able to open/close a door at your A/C.
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Old 4th Apr 2012, 19:00
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Thanks for looking that up, but I suspect that if the problem wasn't a STAB TRM DISAGREE the PSEU light wouldn't go out after the procedure, right? Anyhow, personally I am not sure I would know how to close the hatch if an engineer hadn't shown me how Not something us pilots are supposed to know from a training standpoint.
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Old 4th Apr 2012, 19:32
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Originally Posted by STBYRUD
Thanks for looking that up, but I suspect that if the problem wasn't a STAB TRM DISAGREE the PSEU light wouldn't go out after the procedure, right?...
Most likely yes, but if you guess, you are not sure.
I prefer facts.
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Old 5th Apr 2012, 11:07
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Thank you guys for reply, do you know where to find some more reference about the PSEU? Even if it is for maintenance personnel or what ever. I am sure that they tried to re-trim before unloading paxs, I think that that idea came from technical department. Not sure
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Old 5th Apr 2012, 12:18
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Originally Posted by noox89
...do you know where to find some more reference about the PSEU? Even if it is for maintenance personnel or what ever. ...
You can get more info about the PSEU in the AMM chaper 32-09.


Originally Posted by noox89
...I am sure that they tried to re-trim before unloading paxs, I think that that idea came from technical department. Not sure
There are more than 230 different faults, which the PSEU can display.
The trim is a possible solution for only one of them.
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Old 6th Apr 2012, 18:26
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To add a little to what others have said. The Pseu monitors the landing gear compressed sensors, operates the air/ground relays, sends air/ground discrete signals, provides landing gear position indication and warning, landing gear transfer valve control, landing gear not down warning, speedbrakes extended amber light control, takeoff (aural) warning and door warning.

The cycling of the stab to clear a stab trim disagree nuisance fault does not apply to aircraft built after 12/09 line #3100, or any aircraft that have been updated. One way to eliminate this fault from consideration without doing a bite check is to look at where the stab is positioned. If it isn't at the edge of the green band it's not the source of the fault light.

The scenario the OP described, the fault was a no-dispatch fault. I would have had the pilot perform the bite check. The only potential issue I see would be how it is documented/approved within the airlines maintenance program. Once the fault was known, it could be determined whether it could be a potential nuisance fault or something that needed to be addressed before dispatch.

Lots of information is available if you have access to myboeingfleet.com, such as fleet team digest, maintenance tips, service letters, service bulletins, etc... Just do a search for pseu.
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Old 6th Apr 2012, 20:12
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You can definitely clear faults yourself if your airline authorises you to do so. It is not particularly difficult. However you need a clear set of instructions as the flow is not particularly intuitive. I remember a time around six or seven years ago when I regularly used to reset the PSEU system in the forward electronics compartment. Funnily enough since then I cannot remember having this problem.
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Old 7th Apr 2012, 16:08
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Lederhosen, that would coincide with the last PSEU hardware upgrade to the -4 MOD A, combined with the latest software update it became the -5. The -4 MOD A was introduced in late 2005 with the -5 released a year later.
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Old 7th Apr 2012, 17:56
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Definitely an improvement!
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