Re: Fuel Dump Question

Date:         03 Nov 98 02:05:38 
From:         JF Mezei <jfmezei.spamnot@videotron.ca>
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STeveC01e wrote:
>     I'm not able to answer your specific question, but regarding the
> circumstances, I suppose if the Flight 111 had a electrical fire in a major
> bus, then once the Fuel Dump was initiated, then the crew would NOT be able
> to stop it IF they lost all power.

There have been other comments that on the MD11, the pilots would enter
the amount of fuel to keep and everything else is done automatically.
There have been comments about valves shutting off automatically. Other
comments about pumps used to throw the fuel out, while others mentioned
it was done by gravity.

It seems to me that fuel dump is used for emergencies. Right? And in
emergencies, power is something which is realistically lost, right? Are
the various valves designed to mechanically shut off when power is lost?

I went through the FA 25.1001 and found that for turbine engines:

    (f) For turbine engine powered airplanes, means must be provided to
    prevent jettisoning the fuel in the tanks used for takeoff and
    landing below the level allowing climb from sea level to 10,000 feet
    and thereafter allowing 45 minutes cruise at a speed for maximum
    range. However, if there is an auxiliary control independent of the
    main jettisoning control, the system may be designed to jettison the
    remaining fuel by means of the auxiliary jettisoning control.

Question:
    Since dumping of fuel is used for an emergency which requires the
    plane to land ASAP, (are there other uses?), why would the FAA want
    the fuel dumping system to retain enough fuel to climb and fly for
    45 minutes? Is this to allow for a missed approach? Do missed
    approaches really take that long, do planes really climb back to 10k
    feet?

    Is the dumping of fuel something which is done in circumstances
    which are not actual emergencies and which require the plane to
    abide by congested airport queing and waiting (thus requirememt to
    stay in air 45 minutes) or is fuel dump done only in circumstances
    requiring immediate landing and thus declaring emergency which gives
    the plane immediate access to the runway of its choice?

Question:
    If it allows for an auxiliary system which dumps all of the fuel,
    and such system has no requierement for a minimum reserve (5 minutes
    flight?), what's the point of the first fuel jettison system? Or is
    such system used only for maintenance purposes and not to be used by
    pilots?

Question:
    Why does the FAA not mention a need to reduce to a bare minimum is
    the amount of fuel so that if the landing doesn't go too well (UA
    232 comes to mind), the resulting fire will be as small as possible?
    Seems to me that 45 minutes worth of fuel is a lot.