Fire alert

[Hardy Heinlin]

Good evening,

it's so long ago, I can't remember exactly, but I do recall from sim sessions that you should wait a few seconds when the fire handle is pulled as it could be that the fire will go off without using an extinguisher bottle. So, how long would you wait? 3 seconds? Perhaps 5?

Also, when a bottle is used and the fire doesn't go out, how long do you wait until you fire the other bottle?

How great is the "inertia" of those fire detector loops? When the fire is extinguished, it certainly takes a while until the loop has cooled down to remove the fire alert on the flight deck.

Like in the big sims, PSX offers 4 fire intensities:

- No bottle required
- 1 bottle required
- 2 bottles required
- Inextinguishable

(I have yet to decide what consequences should arise when a fire keeps burning for a long time. Maybe a fatal explosion after ca. 30 minutes.)


Cheerio,

|-|ardy

[marcom]

(I have yet to decide what consequences should arise when a fire keeps burning for a long time. Maybe a fatal explosion after ca. 30 minutes.)

I think there are quite a few interesting consequences:
- Hyd leak / ovht due to "melted" EDP
- Severed control cables on that side
- Severed electrical cables? (So a fire in engine 2 or 3 could cause generator 1 or 4 to fail as well?)

Or would this be too Hollywoody?  

[Will]

If we're talking about engine fires, I thought the engine was supposed to burn for a whole and then fall off the wing.  But I'm probably wrong.

I like marcom's idea of a cascade of additional failures, random but logical, building slowly as things got worse and worse...

[Jeroen Hoppenbrouwers]

I presume whatever happens should be survivable anyway, by appropriate and timely pilot action, else there is little purpose in training for the scenario. Kobayashi Maru, anyone?


Jeroen

[Mariano]

Hardy,

On the 767 (Boeing QRH) it says to wait 30 seconds after firing the first bottle. In the sim, after placing the Fuel Control Switch to CUTOFF, I wait about 5 seconds before firing the first bottle.

On other airplane sims, I used to wait a bit longer (I would much rather wait longer than five seconds on the 767 sim, but instructors don't seem to like that very much.) The other airplane types have much older engines (RR early fans) and maybe because the detector loops aren't as good/modern/reliable as the 767's, they allowed us to wait a bit longer.

I have also wondered about how long to wait before firing the first bottle. There doesn't seem to be a uniform answer. I guess it depends on whom you talk to. Just my take.

Mariano.

[John Golin]

If we're talking about engine fires, I thought the engine was supposed to burn for a whole and then fall off the wing.  But I'm probably wrong.

I like marcom's idea of a cascade of additional failures, random but logical, building slowly as things got worse and worse...

I think I heard somewhere that this was changed? would be interesting to know...

[Jeroen D]

From my (old) KLM and Cargolux AOM:

after 30 seconds, if FIRE ENG is still displayed
- Engine FIRE Handle ROTATE TO OTHER BOTTLE

It doesn't say anything about waiting a few seconds before pulling the fire handle in the first place.

[Will]

I presume whatever happens should be survivable anyway ... else there is little purpose in training for the scenario. Kobayashi Maru, anyone?

'Ardy and his original sim have a long and complicated relationship with the Kobayashi Maru.  Perhaps one could be training prayers?  Humility?

Seriously, it would be good to have a scenario that required landing, shutting down, and evacuating within 40 minutes +/- (random (1-20)) ...

[Roel Raeven]

I have asked this question to my cousin (744 jockey Cargolux)
He says there is no time limit for firing first bottle, but in praxis you always wait a couple of seconds to confirm everything. (step 1 to 4 heart/memory items)
Important is to hold the fire switch for 1 second in the rotated position.
Below is from the manual:

FIRE ENG 1, 2, 3, 4
or
Engine Severe Damage or

Separation

FIRE ENG 1, 2, 3, 4 or Engine Severe Damage or Separation

Condition: One or more of these occur: •Engine fire warning

•Airframe vibrations with abnormal engine indications

•Engine separation •Turbine overheat detected

1  Thrustlever
(affected engine) . . . . Confirm. . . . . . . . . . Idle

2  FUEL CONTROL switch
(affected engine) . . . . Confirm. . . . . . . CUTOFF

3  Engine fire switch
(affected engine) . . . . Confirm. . . . . . . . . . Pull

4 If the FIRE ENG message is shown:

Engine fire switch
(affected engine) . . . . . . . . Rotate to the stop

and hold for 1 second

If after 30 seconds, the FIRE ENG message stays shown:

Engine fire switch
(affected engine) . . . . . . . .Rotate to the other stop and hold for 1 second

[AI744]

On many aircraft types you wait 10 seconds before firing the bottle... So that agent has maximum chance of working.

Then after firing th first bottle you wait 30 seconds.... The airbus will count this down for you on the ECAM.

[Hardy Heinlin]

Re consequences again ...

Could an engine fire cause so much heat in the EDP that it would lead to a hydraulic fluid overheat alert? I don't know where all the hydraulic fluid temperature sensors are. I guess a nacelle fire isn't much hotter than, say, 250°C. The hydraulic fluid temp limit is ca. 100°C. If it were 200°C at the pump, it would probably drop below 100°C along the line after a few more meters.

Probably not so realistic.


|-|

[Jeroen D]

On many aircraft types you wait 10 seconds before firing the bottle... So that agent has maximum chance of working.

I don't understand why the agent would work better/more effecient if you wait 10 seconds? Could you explain?

Jeroen

[John H Watson]

I don't understand why the agent would work better/more effecient if you wait 10 seconds?

One possibility:

Pulling the fire handle shuts down the engine, and, perhaps, with less air flow going through cooling ducts (to the undercowl area), it gives the extinguishant more of a chance to stay under the cowls. BTW, extinguishant does not go into the hot core or coldstream. It would simply be blown away)

I don't know where all the hydraulic fluid temperature sensors are.

They are up in the engine strut area (not on the engine).

Rgds
JHW

[Jeroen D]

Pulling the fire handle shuts down the engine, and, perhaps, with less air flow going through cooling ducts (to the undercowl area), it gives the extinguishant more of a chance to stay under the cowls. BTW, extinguishant does not go into the hot core or coldstream. It would simply be blown away.

Maybe, although in full flight, 10 seconds of 'spool down time' might not make that material a difference?

By the way, what is the "agent" these days? Is it a Halon type of gas, or foam or something very different?

I have a few simple diagrams, but it seems the agent, whatever it might be, gets introduced right underneath the cowl, ie around the core, the by pass area. So you'd think no matter what it'll get blown out.

Unless you release sufficient agent to fill the total volume taking into account whatever volumes that gets blown out, how do you put out the fire??

[Jeroen Hoppenbrouwers]

Jet engines look simple but are not. There definitely is a cavity around/against the core that is not exposed to the cold stream; all the auxiliary devices are there. It is here that a fire can be extinghuished. In the core or cold stream areas, cutting off the fuel supply would kill any fire instantly, as there is nothing else to burn (I think). Additional stuff may be outside the cold flow.


Jeroen

[John H Watson]

The engine accessory gearbox, fuel metering units, fuel pumps, elec generators, engine driven hydraulic pumps, starter, EEC's, etc, are all located outside of the coldstream duct.

 If you look at Jeroen's picture the grey box at the bottom of the engine is the accessory gearbox. This is hidden under the Fan cowls, and apart from cooling airflow to specific devices, the hot/cold airstream has no contact with those previously mentioned items.

The hot core is in the heart of the engine, and well away from anyting important.

[Aidan]

There are many reasons why a jet engine fire may continue to burn despite most fire handles cutting off all inflammable fluids feeding to the engine. One of the more common reasons is an engine oil fire that can occur when an oil line is broken such as what happened to QF32 from Singapore to Sydney.

There was a random, possibly far fetched statistic floating around some time ago that 80% of engine fire indications are false.

I believe FAA and JAA design certification still requires that the engine pylons can be burned through so that the engine will fall off before the wing tanks burn through.