Fire extinguishers after abort

[Shiny side down]

B737 and B757
After abort, during Engine fire recall items, firing both bottles.

I was always of the understanding, and recently confirmed by someone I respect very highly, that there should be a delay between firing the bottles, to allow them each to fully discharge. Otherwise, one may not be fully discharged, ad so you lose the benefit of part of the contents. As they utilise the same plumbing, to route to the same outlets, there needs to be a delay.

At another organisation, I have been told that both are to be fired into a burning engine, without a delay between them.
ie. Rotate the fire handle, orange discharge light, rotate the handle, orange discharge light. With no delay between seeing the first discharge light, and rotating for the second bottle.

In the air, it's 30seconds between discharges, to allow the full discharge and note any change or lack.

Is the discharge light related to drop in pressure, or simply that the squib has fired?

I feel the subtle difference during the ground related drill is being lost.


Comments?
Tech response?

[captjns]

The BOTTLE DISCHARGED light illuminates when the respective bottle pressure decreases below circa 250 PSI.

Chances are the fire brigade is on the scene able to fight any fire that may be present. Important to know, 30 seconds can mean the difference of survival or death if a fire actually exists.

[fireflybob]

Have seen it done both ways by different operators!

capjns, agree with your sentiments but there a few airports where I wouldn't be too surprised if it took a few minutes before the fire trucks were on the scene in the event of fire after a rejected take off!

For a liability point of view, follow your company procedures. If they advocate disregarding the 30 second delay then that goes against Boeing - just make sure it's in writing from the Company and keep a copy for reference.

[lomapaseo]

Has the fuel dissipated

has the ignition source stopped (cooled etc.) ?

If so go ahead and fire your last remaining bottle according to SOP

If not why not wait between discharges to give it a chance ?

[Capn Bloggs]

If they advocate disregarding the 30 second delay then that goes against Boeing
What exactly is the Boeing procedure for an engine fire on the ground in realtion to the two bottles? The QRH procedure for an engine fire is obviously aimed at an airborne situation (ISOL switch, packs, start APU, fuel balance).

[Dan Winterland]

As for Boeings, I've only flown the 747 and the installation we had was one bottle per engine with the option of being able to discharge the adjescant engine's bottle if the first didn't do the job. The advice was not to fire both at once becuse the two systems were unified though a shuttle valve which would allow the bottle with the higher pressure to discharge. The danger of this system is that if the bottles become evenly matched in pressure, the shuttle valve could stick in the middle and the burning engine would get the contents of neither.

[grounded27]

Is your engine burning or is it a bleed leak? Chop fuel, pull the handle and take a breath. If it is a fire and you can not extinguish with one your chances on the 2nd are less, I view the 2nd bottle as more of a redundant system than an effective one.

[de facto]

Chances are the fire brigade is on the scene able to fight any fire that may be present. Important to know, 30 seconds can mean the difference of survival or death if a fire actually exists.

True.
30secs is quite long when an evacuation should be done in 90secs or less.

[RAT 5]

"30secs is quite long when an evacuation should be done in 90secs or less."

And that is from the order to evacuate. Now that Boeing have advised it should be a 'read & do' checklist it takes quite a few seconds to reach the evacuation order. Any opinions why it is no longer a memory drill?

[captjns]

To ensure all required steps are carried out in accordance with the operator's approved non-normal procedures. Read and do also ensures proper handling of the fire bottles based on the current situation.

[mustafagander]

RAT 5

It's a "read and do" because you can not possibly recover from a screw up so spend a few extra seconds and get it right.