Jettison Myths

[Wizofoz]

I know a lot of this got discussed a few years ago, but I have found a great many people still perpetuating these ideas in training, when it comes to fuel jettison:-

Myth 1:- Don't jettison in a hold while descending.

Does anyone have any reference that this might actually be a problem? That, in a standard holding pattern, you might "Catch your fuel", or that it would be a problem if you did?

Myth 2:- Don't jettison near a Thunder Storm.

Well, it's a good idea to not get TOO close to active CBs at any time, but is there actually any learned material that suggests it is any MORE hazardous while dumping fuel?

I'm sure this will generate opinions, but really, I'd be more interested any hard data that supports or debunks either concept.

[FE Hoppy]

Fuel is dumped isn't it? Stores are jettisoned.

Myth 2 was written into the fuel dumping checklist on the L1011 and Nimrod.

Having flown through someone else's dumped fuel I can say that we got ITT rise and fuel smell in the cabin. As for dumping while descending in the hold it would depend on your decent rate and the wind conditions as to whether you would encounter your own fuel on the way down.

[aviatorhi]

Neither one is a myth.

Shutting off HF radios and radar is a good idea as well.

[8che]

No Hoppy,

Fuel is Jettisoned. Thats why Boeing have the "Fuel Jettison" QRH check lists.

The only dumping that takes place is when the skipper takes a physiological break.

Boeing recommend not to Jettison in the hold and caution descending at the same time.

Myth 2 seems sensible but then you shoudnt be in a thunderstorm at any time.

p.s 4000ft AGL limit from the manufacturer. We use 5000ft min

[oxenos]

Many moons ago I was the co-pilot of a Mk. 3 Shackleton when we had a translation unit failure. We were very heavy, could not fully feather the prop, and could not maintain height without the Vipers.The Vipers were then limited to only a few minutes at full power.
There was no option but to jettison fuel (Avgas, of course) with the Vipers running, which had not been tried. The jettison pipes were only about 6 feet outboard of the Viper jet pipes. We half expected "reheat", but it was all a non-event.

[Machinbird]

We used to dump fuel (JP5) regularly in preparation for landing aboard ship. Sometimes you would fly through the formation lead's plume (emanating from the wing fold area). We tried to keep the intakes out of the plume of course, but more than once I had my windscreen washed:}. Never had problems. Never heard of any but not saying there were none.
Having said that, I can faintly remember an airline accident involving fuel dumping probably in the late 1950's off the east coast of the US.
Wouldn't be surprised if some of these restrictions on dumping/jettison of fuel date from the piston engine era.

[Wizofoz]

Neither one is a myth.

Shutting off HF radios and radar is a good idea as well.

Are you saying either has ever actually caused a problem, or that data exists saying that ir could?

[aviatorhi]

Are you saying either has ever actually caused a problem, or that data exists saying that [it] could?

The latter. Just how on the ground the Radar and HFs aren't supposed to be operated during fueling. Under certain conditions you can get some pretty interested arcing occurring on the radome and throughout the airframe.

[FullWings]

I can see how flying through a cloud of your (or someone else's) fuel might not be a great idea - mostly the smell and smeary windscreens, I'd think - but what's the worst that could happen if you dumped near a thunderstorm, low level with the radar on while trying to call Mumbai on HF? You're not going to have flames chasing back up into the wing, like in cartoons. Mythbusters tried it with petrol and were down to almost walking pace before the flames caught up and even then, nothing happened.

F111's used to deliberately "dump and burn" for airshows but they had to have the reheat on to ignite the fuel, AFAIK.

[aviatorhi]

You're not going to have flames chasing back up into the wing, like in cartoons.

When the guys who designed the thing tell me it's a bad idea I tend to at least give it a listen. I know of at least one aircraft that literally "exploded" out of the sky, granted it was in the 30s and due to a design issue, but it has happened.

The Samoan Clipper (http://www.planecrashinfo.com/1938/1938-3.htm)

F111's used to deliberately "dump and burn" for airshows but they had to have the reheat on to ignite the fuel, AFAIK.

Too bad we're not all in F111s then.

[Wizofoz]

When the guys who designed the thing tell me it's a bad idea I tend to at least give it a listen.

That was exactley my point- can you tell me where the manufacturers, or any one else in a position to make such a judgement, HAS told anyone either scenerio should be avoided?

I know of at least one aircraft that literally "exploded" out of the sky, granted it was in the 30s and due to a design issue, but it has happened.


Yes, but was that due to any factor we are discussing here? And i DO think design has moved on a little since the clipper days.

[sleeve of wizard]

Fuel Jettison
Fuel jettison should be considered when situations dictate landing at high gross weights and adequate time is available to perform the jettison. When fuel jettison is to be accomplished, consider the following:
• ensure adequate weather minimums exist at airport of intended landing • fuel jettison above 4,000feetAGL ensures complete fuel evaporation • downwind drift of fuel may exceed oneNM per1,000feet of drop
• avoid jettisoning fuel in a holding pattern with other airplanes below.

[Wizofoz]

IGH,

Interesting, but from your quoted text:-

Ops Manual mandated a "clean" configuration for fuel dump; tests showed no significant hazard in any configuration Lockheed next tested ignition of dumped-fuel: test Tunnel, scale model wing and dump system ==> test proved it was impossible to involve the Wing in fire under any condition (unless a fire was maintained within the Wing itself.)

Seems like under idealised conditions, you MIGHT be able to ignite the vapour trail, but even then it is unlikely to pose a hazard.

Still, that is more what I was looking for in terms of SOME type of evidence, rather than just "What I heard" type reasoning.

[aviatorhi]

@Wizofoz

The text provided by sleeve of wizard is exactly what I have seen in the Flight Handbook of every Boeing aircraft capable of dumping fuel.

Sure, design has moved on, but common sense is not a common virtue. I would be extremely ticked at the guy who dumped fuel onto me (even if the manuals allowed it). Also, while I think the odds are quite low that a stray lightning bolt will set you ablaze, it's not something I plan on testing, unless I'm already on fire and need to land ASAP. That being said, don't forget, landing overweight is always an option if the situation warrants it.

[Wizofoz]

avi,

Sure, that's what my manual says too.

There is nothing there that says anything about either of the scenarios I outlined. Not dumping on others has nothing to do with "Catching your own fuel", and it doesn't seem like "The guys that designed them" actually publish any material that suggests it's possible.

Yes you can land overweight if necessary.

Can you provide ANY text that gives guidance as to how close a TS needs to be before that is preferable to jettisoning to MLW for fear of it setting the trail ablaze, and that fire spreading to the Aircraft?

If you want to cite manufacturers recommendations in favour of your arguments, you need to CITE manufacturers recommendations- I suggest you cannot do so.

[aviatorhi]

Correct me if I'm wrong, but isn't the text in the manufacturers flight handbook a manufacturer reccomendation?

In the US, ATC is advised with the following:

9-4-4. SEPARATION MINIMA

Separate known aircraft from the aircraft dumping fuel as follows:

a. IFR aircraft by one of the following:

1. 1,000 feet above it; or in accordance with para 4-5-1, Vertical Separation Minima, whichever is greater.

2. 2,000 feet below it.

3. 5 miles radar.

4. 5 miles laterally.

b. VFR radar-identified aircraft by 5 miles and in accordance with para 5-6-1, Application.

As far as thunderstorms are concerned, if you want to fly through/near the stuff that makes St. Elmo go nuts on the windscreen and (occaisionally) leading edges while trailing a plume of kerosene, go for it.

If you want me to dig out Boeings research data, I can only point you to;

AERO - Overweight Landing (http://www.boeing.com/commercial/aeromagazine/articles/qtr_3_07/article_03_2.html)

Their Flight Handbooks

There used to be another PDF file on their site which I had a link to in the past, but since they redesigned it I haven't been able to find it (actually still comes up in a google search but now goes to an error page). If I find it I'll be more than glad to pass it on to you.

[bubbers44]

Our airline said it was ok not to dump fuel and land overweight if it was as safe as landing as MLW. I thought about this for a minute and visualized my FAA hearing landing overweight to save money and decided I wasn't going to do it.

A month later I took off in a 727 for South America with a tropical storm enroute. I got a plane with a radar written up as intermittent and got the usual ground checked ok fix. There was a bump on the runway just as we rotated, the radar failed. We pulled circuit breakers and talked to maintenance but still no radar. We dumped to max landing weight and returned for a bad radar. I would do it again before flying in known thunderstorms with no ATC radar and no aircraft radar.

[Wizofoz]

Avi,

We may be talking at cross purposes.

The "Myth" I was mentionong in my OP had nothing to do with seperation from other aircraft, which I agree is an essential part of Jettison planning.

It had to do with the notion of not descending in the hold while jettisoning, for fear of YOUR OWN AIRCRAFT hitting YOUR OWN FUEL- and THAT is something I believe there is no mention of in any manufacturers documentation.

Thanks for the link- I am reasonably conversent with Overweight v Jettison, and it will always be a judgement call on the day.

And yes, I'd be worried if I was experiencing arcing and needed to jettison- but wondered if anyone had any actual data quantifying an additional risk. Much as it seems a scary thing to do, I don't think a realistic risk actually exists.