Why can't the French dump fuel?

The last link provided by Kev has the likely answer:
"The primary reason to burn off the extra fuel was that a heavier plane
has a faster landing speed. Since a slower airspeed on landing was the
objective in this case, the course of action was to lighten the load by
burning off some fuel and when landing, lower the nose gear at as slow
an airspeed as possible."

Joe,
You sound like an EXCELLENT advocate for having the ability to dump
fuel too!!!

-Robert

The FAA certification requirement for a fuel dump system is a takeoff
weight that is greater than 135% (I think) of the max landing weight.
They don't add the complexity and cost of a dump system unless it is
required for certification.

The 707-123 I flew had a empty weight of 120,000 lbs, max TO weight of
256,000 lbs, 112,000 lbs of fuel, a max landing weight of 190,000
pounds,(135%) had a dump system. A 757-200 at 256,000 lbs carries
83,000 lbs of fuel, max landing weight of 198,000 lbs (130%) does not.
BTW the 757 with 29,000 lbs less fuel has the same range as a 707-100
with the same passenger load.

The 707 system has standpipes that let you dump only to get you down
to max landing weight, leaving in our case about 70,000 lbs of fuel.
That being said, I'd have flown around several hours after dumping, if
there was no immediate emergency , to get as light and non-flamable as
possible before landing. Their gear problem was not an emergency and
I doubt the crew declaired one even though they asked for the
equipment. Emergencies require immediate action. (think fire) BTW a
single engine failure is not classified as an emergency either. The
aircraft is certified to climb at max takeoff weight on a single
engine.

I'm sure the airlines, EPA, and everyone else would rather the fuel be
burnt as normal rather than dumped into the air and sea. In an
emergency, planes that don't have a dump system will do an overweight
landing and and have to do an overweight landing inspection prior to
next flight. Given the choice, it's better to burn it down than do
the inspection.

Don Hammer wrote

The FAA certification requirement for a fuel dump system is a takeoff
weight that is greater than 135% (I think) of the max landing weight.
They don't add the complexity and cost of a dump system unless it is
required for certification.

Don, the rules have changed since you and I flew those old Boeings. :-)

Section 25.1001: Fuel jettisoning system.
(a) A fuel jettisoning system must be installed on each airplane unless
it is 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 the same as that used in meeting
the applicable takeoff, approach, and landing climb performance
requirements of this part.

(b) If a fuel jettisoning system is required it must be capable of
jettisoning enough fuel within 15 minutes, starting with the weight
given in paragraph (a) of this section, to enable the airplane to meet
the climb requirements of §§25.119 and 25.121(d), assuming that the fuel
is jettisoned under the conditions, except weight, found least favorable
during the flight tests prescribed in paragraph (c) of this section.

(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.


Bob Moore
ATP B-707 B-727
PanAm (retired)

Bob Moore wrote:

25.121(d) at maximum takeoff weight

This is how it was explained to me; an ex-member of our club that flies for
"a major" simplified it to "one-engine-out missed approach": if the plane
can do that at t/o weight, no dump system required.

This is distinct from the maximum landing weight, which involves other
factors. In an emergency, therefore, a pilot might need to make an
"overweight landing".

- Andrew

I'm sure the airlines, EPA, and everyone else would rather the fuel be
burnt as normal rather than dumped into the air and sea.


I heard that the environmental impact of dumping fuel is not as bad as
it might seem. As the volatile fuel is sprayed into the air it tends to
oxidize and the result is similar to burning it in the engine. I am not
too sure of this when considering the complex chemistry of turbofan
combustion in flight. From the combustion chamber, out the nozzle and
through the downwash behind the plane the combustion reaction
continues. Dumping fuel sprays it into turbulent air without the
initial combustion and expansion so it is likely much different. I was
a payload integration engineer in support of the NASA DC-8 (which had
the ability to dump of course) on the SUCCESS mission to fly planes
behind and around each other to sample the exhaust products and
characterize the chemistry. The pilots had to be careful not to get
caught in the tip vortex.

http://cloud1.arc.nasa.gov/success/d...60418.hil.html

In the above photo our engineering group installed the canoe sized
instrument fairing on the side of the plane just forward of the aft
service door. We also installed the pod under the forward fuselage. As
the elevator is tab powered and the fairing is in front of it, we were
crossing our fingers during the taxi test and flight test.

http://uap-www.nrl.navy.mil/dynamics...s2May1996.html

http://raf.atd.ucar.edu/~dcrogers/GRL/grl.html

http://cloud1.arc.nasa.gov/success/

James

"jbaloun" wrote:

I'm sure the airlines, EPA, and everyone else would rather the fuel be
burnt as normal rather than dumped into the air and sea.

I heard that the environmental impact of dumping fuel is not as bad as
it might seem. As the volatile fuel is sprayed into the air it tends
to oxidize and the result is similar to burning it in the engine.

Then why are gas pumps in many places fitted with systems to capture the
vapors from fueling? Why is barbeque lighter fluid banned in many
jurisdictions? Why is there a push to ban oil-based paint and thinners?

The reality is that unburned hydrocarbons are a major source of air
pollution. The occasional fuel dump will not have a huge effect on the
environment, but it is still better if the fuel is burned in a well-
maintained engine.

The reality is that unburned hydrocarbons are a major source of air
pollution. The occasional fuel dump will not have a huge effect on the
environment, but it is still better if the fuel is burned in a well-
maintained engine.

I did not say that it would be better to dump fuel rather than burn it
in the engine. Burning in the very efficient modern turbofan is a
better way to dispose of the high energy fuel, maybe the best way (just
from a chemestry point of view let alone the value of flying a plane).
I did not say there would not be an environmental impact, just that the
fuel dumped in flight is likely oxidized and would not stay in the air
or land on the ground in the form of raw fuel. I understand that fuel
dumping is very rare compared to the number of flights per year. It is
so rare that the any regulatory agencies may not be concerned about the
yearly amount of fuel dumped as compared to the overall amound of fuel
burned. The cumulative impact of automobile (gasoline) refueling vapors
being released is much greater than that due to (kerosene) fuel dumped
in flight. In addition, dumping fuel is almost always done to respond
to an urgent situation on an aircraft where the environmental cost is
outweighed by flight safety.

Aircraft engine manufacturers have made amazing strides in improved
efficiency. And still researchers are considering how to continue to
improve engines while reducing emissions. It would have been
interesting if the SUCCESS mission took measurements of fuel being
dumped in flight. If I had thought of it I would have suggested it
then. Oh well.

James

"jbaloun" wrote

I did not say there would not be an environmental impact, just that the
fuel dumped in flight is likely oxidized and would not stay in the air
or land on the ground in the form of raw fuel.

I think you are making a mistake, in you use of "oxidized" in this case.

"Oxidized" is combining it with oxygen chemically, as in "burning". In this
case, there is no combining chemically, but only vaporization, as in
evaporating. In both cases, no fuel reaches the ground.
--
Jim in NC

Why is barbeque lighter fluid banned in many jurisdictions?

You're kidding, right?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
Why is barbeque lighter fluid banned in many jurisdictions?

You're kidding, right?

California. Aspen also had a shot at it, but I think the law failed to pass.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.