Re: Question: Fuel Dumping

Date:         31 Jan 97 14:29:23 
From:         michael.f.lechnar@boeing.com
Organization: nams
References:   1 2 3
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In article <airliners.1997.345@ohare.Chicago.COM> Pete Finlay <pete@meads.demon.co.uk> writes:
>In article <airliners.1997.268@ohare.Chicago.COM>, "Brian A. Reynolds"
><bareynol@cca.rockwell.com> writes
>
><<my stuff snipped>>
>
>>Hi Pete, sorry, have to agree with Mike.  FAR 25.1001 Fuel jettisoning
>>system.  (a) A fuel jettisoning system must be installed unless it si
>>shown that the airplane meets the climb requirements of 25.119 and
>>25.121(d) at maximum takeoff weight, less the actual or computed weight
>>of fuel necessary for a 15-minute flight comprised of a takeoff,
>>go-around, and landing at the airport of departure with the airplane
>>configuration, speed, power, and thrust thte same as that used in
>>meeting the applicable takeoff, approach, and landing climb performance
>>requirements of this Part.  Landing gear is addressed in 25.721 and the
>>requirements deal with the adequacy of the landing gear, reserve
>>capability, and testing.
>
>What you have put forward is the FAA's view on aviation. Please bear in
>mind that this view is not necc. reflected round the rest of the world.
>A very large proportion of the world do not operate under FAA rules, but
>rather under their own civil aviation authority regulations.
>
>Nor do F.A.R.'s enter into the Flight Crew's consideration when faced
>with a large aircraft that is able to take-off at 1.3 times it's maximum
>structural landing weight due to the large amounts of fuel we carry.
>
>If the question was why do large aircraft have to dump fuel, then I
>still believe I am correct: in order to get down to max. structural
>landing weight.

You are both right.  But dumping fuel for performance purposes is the law
and dumping to get below max landing weight is just a convenience.
Overweight landings require a structural inspection before the next flight.
I don't know the exact requirements, but it's probably more than a fair
trade to dump the fuel to save the expense and time of the inspection.
I also acknowledge the consequent improvement in landing speeds and
handling.

Regarding the FAR's "limited" applicability outside of the U.S.:  Yes most
of of the world has their own aviation authority.  However, almost all of
them have pretty much rubber-stamped either the FAA, CAA or JAA flavors
of the rules.  The rules on approach and landing climb requirements are
not significantly different between them.  There are some additional
requirements imposed by the CAA such as "reduced visability climb" which
also come into play.  The bottom line is that you can't schedule a landing
weight that does not simultaneously satisfy both the climb requirements
and landing field length requirements.

Typically twin airliners are never limited by landing climb performance.
At max takeoff weights, the fuel burned during the turnback to the airport
(return to land) will take the weight below the performance limit.  As
twins get bigger, such as the 777 and 767-300ER, fuel jettison systems
have had to be added because the 15 minute fuel burn is not enough.

Mike Lechnar
Aircraft Performance Engineer
"If I was speaking for Boeing, I wouldn't be doing it here."