Fuel Dump system question, necessity

[QuEsT147]

Hi guys

I would like to find out, why for some aircraft a fuel dump system is necessary. According to regulations, an aircraft must have a fuel dump system if it is unable to comply with certain climb requirements, or so, I do not know the exact definition.

But here is the question... The aircraft must be able to take-off safely with one engine inop at MTOW, then how is it possible that it cannot conduct a go-around at weight which is always less than MTOW without dumping fuel?

Maybe I do not understand it correctly, please explain it to me

Thanks much for help

QuEsT147

[kijangnim]

Greetings,
You have to take into consideration, that you have flaps (more drag) gear down (more drag)
It is not always that you are Approach/landing climb limited

[Avtrician]

Also to be taken in to consideration is the max landing weight. If the craft is overweight for landing, the undercarriage may collapse, puncture the wings and cause a massive / fire explosion, generaly believed to not good. Much better to dump the excess load and land safely(ish).

[Mad (Flt) Scientist]

I do not know the exact definition.

The requirement as of amdt 25-108 in 14 CFR 25 is:

§ 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.

[Rainboe]

zzzzzzzzzzzzzzzzzzzzz

[Roadtrip]

Many 767s do not have a fuel dump system.

[NSEU]

Many 767s do not have a fuel dump system.

767's come in different weights, lengths and fuel capacity. The lighter and shorter ones don't need fuel jettison.

[Bullethead]

And the funny thing about the B767 fuel dump system, you can only dump from the centre wing tank and with full wing tanks and an average ZFW you'll still be well over max landng weight.

Regards,
BH.

[kijangnim]

Greetings,
Bullethead
Center tank have to be empty before wing fuel tanks are used, due to wing to body(bending moment).... In fact the first limitation on the 767 was not allowed 10 tonnes in center tank with less than full tank in the wings, was then improved to 700 kgs in the center tank

[Bullethead]

G'day kijangnim,

Yeah, I realise the CWT is used before the wing tanks, due to wing bending relief, my point was that even though some the B767s I fly have a fuel dump system with any sort of normal ZFW you still can't dump to below max landing weight.

E.g. ZFW 125.0T Max is 130.6T
Full wing tanks 36.0T
AUW 161.0T
Max Ldg Wt 145.1T

There is no fuel dump capability from the wing tanks.

Regards,
BH.

P.S. One of these days I'm going to leave all the typos uncorrected, it makes for much more interesting reading.

[Flight Detent]

Yeah Bullethead...

It's the same setup on the B737 fuel dump system.

Cheers...FD...

[Romeo India Xray]

Forgive my stupidity here, but if dumping from CWT on the 76, is it then possible to interrupt the dump, feed wing to CWT and then re-commence dump?

I have no information or experience of the 767 whatsoever so I am trying to visulize (and learn), as my job could loosely involve some old 200s this side of Christmas.

RIX

[Bullethead]

You can turn off the dump pumps and close the dump valves whenever you wish and also recommence if needs be.

There is no capability to transfer fuel from any tank to any other tank, you can feed either engine from any tank or dump from the CWT only.

I'd be surprised if a 200 series B767 had a fuel dump capability.

Regards,
BH

[Romeo India Xray]

Bullethead

Many thanks for that. I wont be flying them (I will be relegated/promoted whichever way you look at it, to turboprop land by then), only working closely with people who will.

RIX

[SNS3Guppy]

We're able to land overweight, with a maximum descent rate prescribed, and a requirement for an overweight landing inspection. However, when we plan for a fuel dump, it's the aircraft performance that concerns us, to include landing speeds and distance, more than the weight.