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B 747 Fire Bottle Disch. Discrepancy?  
User currently offlinePopee From Pakistan, joined Feb 2001, 151 posts, RR: 0
Posted (12 years 3 weeks 9 hours ago) and read 2787 times:

On B 4747, instead of measuring the fire bottle pressure, a pr. s/w installed in the line to direct bottle content to engine illuminates the BOTTLE DISCHARGE light in the cockpit.

Is this not a discrepancy ? Discrepancy in a way that in case if any bottle(s) dicharges due to over temperature after walk around check by F/E, no light will lit in the cockpit ? (As discs are used to monitor O/T discharge )

Any comments.

Popee.

11 replies: All unread, jump to last
 
User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 1, posted (12 years 3 weeks 8 hours ago) and read 2776 times:
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The Pressure Sw is on the bottle.

The line Press Sw is only in the Cargo Fire Ext Sys to the Fwd Hold. This is because the lines to the Fwd Hold are of a small diameter so if the bottle is discharged the lines will "choke" with agent which will increase the time before a decrease in pressure is felt in the bottle to bring on the Disch light.

The aft hold doesn't have the problem because of the longer pipe run.


User currently offlinePopee From Pakistan, joined Feb 2001, 151 posts, RR: 0
Reply 2, posted (12 years 3 weeks 7 hours ago) and read 2752 times:

VC-10, I am refering to the engine fire bottles and not the fwd/aft holds. The engine fire bottles don't hv a pr. s/w on the bottle.

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 3, posted (12 years 3 weeks 4 hours ago) and read 2747 times:
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What you say is only applicable to the JT9 installation, all the other engine configuations have press switches on the engine firebottles.

On the JT9 system for an o/press dicharge to occur you require an o/press in the bottle of at least 2400psi at 300Degs F. I would very much doubt that is going to happen in the 30 mins before flight when the FE does his walkround.


User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 4, posted (12 years 3 weeks 3 hours ago) and read 2720 times:

Popee - this applies to the JT9 powered airplanes...
Discharge light will be ON only for INTENTIONAL (MANUAL) discharge of the fire bottle for the engine and APU... a thermal discharge would not illuminate the discharge light, but would blow the red disc of the related bottles...
xxx
But an exception is for the lower cargo fire protection is as follows... again, manual discharge will illuminate the related discharge light... HOWEVER in case of a THERMAL discharge of bottle number 1... OR... number 2... will ALSO illuminate the.... NUMBER 1 discharge light (even if bottle number 2 had the thermal discharge)... this is a famous oral question for FEs, and probably for ground engineers as well...
xxx
I remember in the 707 and the 727, the discharge light was on for a bottle low pressure, after a manual, or thermal discharge... so they changed all that with the 747... dont ask me about the other Boeing planes...
xxx
If you care to know about the 747 with CF6 like VC-10 says it may be different, I will see what my books say about these airplanes... I have no info about the RR powered airplanes...
(s)
Skipper


User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 5, posted (12 years 2 weeks 6 days 19 hours ago) and read 2704 times:

Is this not a discrepancy ? Discrepancy in a way that in case if any bottle(s) dicharges due to over temperature after walk around check by F/E, no light will lit in the cockpit ? (As discs are used to monitor O/T discharge

I never realized this but I think you're correct. Kind of strange that a pressure switch isn't installed directly on the bottle.

A couple of years ago while waiting to pushback a DC10, a momentary brownish haze by the tail caught my attention. Moments later the crew called on the headset informing me of a #2 fire bottle low pressure light.
The bottle thermal discharged due to a bleed leak overheating the bottle.



You're only as good as your last departure.
User currently offlinePopee From Pakistan, joined Feb 2001, 151 posts, RR: 0
Reply 6, posted (12 years 2 weeks 6 days 8 hours ago) and read 2663 times:

I will check my notes for CF6 & RR engines. But let it be on JT9 alone, does it not call for some modification, or is BOEING waiting for some dissaster...


Popee.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 7, posted (12 years 2 weeks 6 days 4 hours ago) and read 2647 times:
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Popee,

Have I not already said it only applies to the JT9 equipped 747?

But let it be on JT9 alone, does it not call for some modification, or is BOEING waiting for some dissaster...

The 747 has been around for in excess of 30 years now. If the disaster was going to happen, it would have happened by now.


User currently offlinePopee From Pakistan, joined Feb 2001, 151 posts, RR: 0
Reply 8, posted (12 years 2 weeks 5 days 7 hours ago) and read 2634 times:

The 747 has been around for in excess of 30 years now. If the disaster was going to happen, it would have happened by now.
Does it imply that no new accidents can happen in aviation ? All accidents happening now r known to us as they r all repeated one ? An accident not happened till now shows no such accident can take place now ?

VC-10, the answers to all these questions is a big NO. Its not a right judgement that as such past 30 years were safe so its future will also be safe although an anamolly is there.

What would u say, if God forbid, it happens this week ???


Popee.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 9, posted (12 years 2 weeks 5 days 6 hours ago) and read 2624 times:
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When Boeing, or any other manufacturer, design these things they calculate the probability of failure. The senario you consider a problem must have a very low probability factor.

Here's another senario on related subject.

You dispatch a 747-400 with one fire loop inop. During the subsequent flight the second loop fails give a fault indication. What do you think Boeing's advice is - continue the flight of Rtn to base ?



User currently offlinePopee From Pakistan, joined Feb 2001, 151 posts, RR: 0
Reply 10, posted (12 years 2 weeks 4 days 4 hours ago) and read 2606 times:

VC-10, yes. The case u r talking about is that the crew gets the information about while in the c/p. What i am saying is they r unware that bottles r discharged after the turn around check by F/E, a situation c/p crew is totally unaware of and getting all ok in the c/p.

BTW the fire warning system will still give any fire wx although test may be u/s.Amazing isn't it...


Popee.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 11, posted (12 years 2 weeks 4 days 4 hours ago) and read 2599 times:
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Popee,
I'm well aware what you are talking about. As I said, Boeing probably considered it a low probaility factor.

The only way the you would get a o/press discharge would be a pneumatic duct leak, in which case if it was hot enough to discharge the bottle you would also have the pylon o/ht warning as well.

Regarding my other senario. I am not saying the test is inop, I am saying EICAS gives a loop fault message in flight


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