Can anyone explain me the theory of light test in B737NG?
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From: earth
Can anyone explain me the theory of light test in B737NG?
During rescent flights , when doing the light test , I got a question, it looks like when put the light test switch in test position , it not just test the bulb of each light, because when some CB pop out , the related system light are extinguished but the bulb of that light is OK. so may i take a guess that the light test is not only test the bulb , but also the status of each system work ? can any system expert explain me how the light test work? i think i will learn more form you reply. THX
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From: earth
amp,
when you pull out a CB, say the speedbrake.the related light(speed brake arm) will not illuminate when doing the test. but the lamps issssssss OK. when you reset the CB, everything returns nomal and good.WHY?
when you pull out a CB, say the speedbrake.the related light(speed brake arm) will not illuminate when doing the test. but the lamps issssssss OK. when you reset the CB, everything returns nomal and good.WHY?
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If you pull any circuit breaker it interrupts the flow of current from source to destination. Normally a lamp is intended to show if such a flow is passing through such a breaker. So as you have pulled a breaker the lamp goes out. However the TEST circuit is situated ahead of the breaker and if the lamp lights then it means the bulb is okay. My brain hurts. I hope you never have a fire in the APU because a fire can be raging in the tail and suddenly the warning lights go out. That does not mean that the fire is out - the wires to the warning system have burned through... so every lamp has to be isolated in such a way as to test the intended function. My brain doubly hurts. So tired....
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From: Skating away on the thin ice of a new day.
172 driver, to give pilots engineers and instructors something to ponder.I think they made it the same as the classic.why ? 
Cant remember.
sky-738 , thats the way it works,pulling the spd brk c/b =no light , pilot thinks hmm something wrong, use NNC or contact engineering. sometimes a light not being on is as much a warning as one being illuminated.
sometimes tripping a breaker will illum a light rather than stop it, ie windshield heat. You have to know your systems and understand what and why you maybe seeing something.
But original point stands, lights test s/w is just that.
Cant remember.sky-738 , thats the way it works,pulling the spd brk c/b =no light , pilot thinks hmm something wrong, use NNC or contact engineering. sometimes a light not being on is as much a warning as one being illuminated.
sometimes tripping a breaker will illum a light rather than stop it, ie windshield heat. You have to know your systems and understand what and why you maybe seeing something.
But original point stands, lights test s/w is just that.
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amp,
when you pull out a CB, say the speedbrake.the related light(speed brake arm) will not illuminate when doing the test. but the lamps issssssss OK. when you reset the CB, everything returns nomal and good.WHY?
when you pull out a CB, say the speedbrake.the related light(speed brake arm) will not illuminate when doing the test. but the lamps issssssss OK. when you reset the CB, everything returns nomal and good.WHY?
If you do that with me in flight or on the ground, Ill smash your head into the CB panel and then make a light test,see if you illuminate,finally
Last edited by de facto; 8th June 2012 at 03:39.
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From: A tropical island.
de facto,
I hope you're kidding about reacting that way to a CB being pulled.
Otherwise...
.
Regarding the subject at hand, I believe the fire handles will remove power from the annunciators for the systems they shut-off / disconnect when pulled, hence lights do not illuminate.
I hope you're kidding about reacting that way to a CB being pulled.
Otherwise...
.Regarding the subject at hand, I believe the fire handles will remove power from the annunciators for the systems they shut-off / disconnect when pulled, hence lights do not illuminate.
Last edited by aviatorhi; 8th June 2012 at 06:30.
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From: IRS NAV ONLY
Systems schematic manual shows (here - not up to date version) that the speedbrake armed light is tested with the use of auto speedbrake CB, so the auto speedbrake CB should not be tripped in order to show when the lights test switch is set to TEST.
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de facto,
I hope you're kidding about reacting that way to a CB being pulled.
I hope you're kidding about reacting that way to a CB being pulled.
CB are not to be touched on ground,Maintenance only is to reset CBs for other reason than a NNC action, especially in such unecessary case.
Otherwise
Peace
Last edited by de facto; 8th June 2012 at 18:32.
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From: ???
De facto I think you are the one in need of that chill pill.
It was a hypothetical question. The poor fellow is trying to get a more in depth understanding of the system. he doesn't need your abuse.
btw on some aircraft there are procedures in place to pull and reset a CB on the ground by flight crew. Resetting a tripped CB is another story.
It was a hypothetical question. The poor fellow is trying to get a more in depth understanding of the system. he doesn't need your abuse.
btw on some aircraft there are procedures in place to pull and reset a CB on the ground by flight crew. Resetting a tripped CB is another story.
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From: A tropical island.
It's a poor attempt at humor, particularly after I asked if it was humor or not.
I see no problem with (as a crew) pulling / resetting CBs (apart from fuel related ones) in flight or on the ground, very useful in troubleshooting and even more useful in disabling systems which aren't performing up to par or are being an annoyance.
One particular airport I flew into regularly a few years ago was not recorded in the TAWS database correctly (database showed it 5 miles away), company responsible for maintenance of said database would not fix it, hence pulling the CB for the warning horns blaring in my ear was the best solution given the circumstance.
Same goes for when I had a stall warning system get stuck in on, scared the **** out of the other guy.
"Recycling" CBs is a non issue for me whatsoever.
As far as resetting is concerned, have no problems with it so long as the system is necessary and consideration is given to the matter.
I see no problem with (as a crew) pulling / resetting CBs (apart from fuel related ones) in flight or on the ground, very useful in troubleshooting and even more useful in disabling systems which aren't performing up to par or are being an annoyance.
One particular airport I flew into regularly a few years ago was not recorded in the TAWS database correctly (database showed it 5 miles away), company responsible for maintenance of said database would not fix it, hence pulling the CB for the warning horns blaring in my ear was the best solution given the circumstance.
Same goes for when I had a stall warning system get stuck in on, scared the **** out of the other guy.
"Recycling" CBs is a non issue for me whatsoever.
As far as resetting is concerned, have no problems with it so long as the system is necessary and consideration is given to the matter.
Last edited by aviatorhi; 9th June 2012 at 10:02.
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It's a poor attempt at humor, particularly after I asked if it was humor or not.
I have yet to reset a CB in the last 9 years....but if i have to,sure I will.
However if maintenance is around, then they will do so and the appropriate work and log entries related to such action.
Please give us a favour,those nuisance cbs you like to pull out.(and those for your trouble shootings and so forth).make sure you push them back in for the next crew.
Last edited by de facto; 9th June 2012 at 15:13.
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Originally Posted by aviatorhi
I see no problem with (as a crew) pulling / resetting CBs (apart from fuel related ones) in flight or on the ground, very useful in troubleshooting and even more useful in disabling systems which aren't performing up to par or are being an annoyance
Do crew members pulling CBs in flight??? for troubleshooting???