smartt1982
Topic Author
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Joined: Sat Nov 24, 2007 11:17 pm

Fuel Dumping And Max Landing Weight

How does it work with regards to Max landing weight. My understanding is that aircraft require a fuel dumping system if their Max Take off weight is significantly higher than the Max Landing weight, does this always apply?
I do know sometimes an aircraft may have to do an overweight landing and this would require as a minimum an inspection by maintenance.
If an aircraft does NOT have a fuel dumping system does this mean that it HAS to be able to land overweight up to its Max take off weight?

tdscanuck
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Joined: Wed Jan 11, 2006 7:25 am

RE: Fuel Dumping And Max Landing Weight

 Quoting smartt1982 (Thread starter):My understanding is that aircraft require a fuel dumping system if their Max Take off weight is significantly higher than the Max Landing weight, does this always apply?

Yes, although the definition of "significantly" moves around a bit.

 Quoting smartt1982 (Thread starter):If an aircraft does NOT have a fuel dumping system does this mean that it HAS to be able to land overweight up to its Max take off weight?

Yes, in the sense that all aircraft can land overweight up to their max takeoff weight. What varies is how much damage you're likely to do in the process.

Tom.

Starlionblue
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Joined: Fri Feb 27, 2004 9:54 pm

RE: Fuel Dumping And Max Landing Weight

 Quoting tdscanuck (Reply 1):Quoting smartt1982 (Thread starter): If an aircraft does NOT have a fuel dumping system does this mean that it HAS to be able to land overweight up to its Max take off weight? Yes, in the sense that all aircraft can land overweight up to their max takeoff weight. What varies is how much damage you're likely to do in the process.

To add to this, it's all a matter of how much risk you need to take in the particular situation.

If the plane is on fire, you land as soon as you can. In this case the risk of not landing is higher than the risk of landing overweight (fast).

If the gear does not come down, you are well served with lowering your weight. If you can dump, you dump. If you can't dump, you circle to burn off fuel.

As was mentioned in a previous thread, landing overweight is not a horrible thing to be avoided at all costs. It is a tool available to the pilots and should be used if the situation warrants it. If you have a fire in the hold, landing overweight and possibly dinging the aircraft is hardly your biggest problem.
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zeke
Posts: 11662
Joined: Thu Dec 14, 2006 1:42 pm

RE: Fuel Dumping And Max Landing Weight

 Quoting smartt1982 (Thread starter): My understanding is that aircraft require a fuel dumping system if their Max Take off weight is significantly higher than the Max Landing weight, does this always apply?

No, even with fuel dump feature, one needs to look at the possibility of needed to return immediately after takeoff, and fuel dumping is not fast enough to make that happen.

 Quoting smartt1982 (Thread starter):I do know sometimes an aircraft may have to do an overweight landing and this would require as a minimum an inspection by maintenance.

The type of inspection is normally related to the type of landing "seen" by the airframe, if it is low impact (less than say 300 ft/min) it would need a different inspection than high impact. A high impact landing at high weights could mean a gear change, even if the inspection found nothing.

 Quoting smartt1982 (Thread starter):If an aircraft does NOT have a fuel dumping system does this mean that it HAS to be able to land overweight up to its Max take off weight?

Normally a figure just under, that being the fuel burn-off to come back around for an immediate landing.
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Goldenshield
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RE: Fuel Dumping And Max Landing Weight

 Quoting zeke (Reply 3):The type of inspection is normally related to the type of landing "seen" by the airframe, if it is low impact (less than say 300 ft/min) it would need a different inspection than high impact.

Depending on the airframe, possibly no inspection at all.
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SlamClick
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Joined: Sun Nov 23, 2003 7:09 am

RE: Fuel Dumping And Max Landing Weight

 Quoting smartt1982 (Thread starter):My understanding is that aircraft require a fuel dumping system if their Max Take off weight is significantly higher than the Max Landing weight

Common misconception. Under US FARs it goes like this. A transport category airplane is required to have a fuel jettisoning system (FAR 25.1001) unless it can meet the climb requirements of FAR 25.121(d) Note that this has absolutely nothing with structural damage considerations for landing. Nobody cares about that. It is about rejecting the landing with an engine inoperative and not crashing. 25.121(d) describes an ability to climb at a 2.1% (for two-engine airplane with an engine inoperative) which is 2.1 feet of elevation gained in 100 feet of horizontal travel. Again it has nothing to do with overweight landings.

Further, since the max ramp weight of a jet is always greater than the max landing weight it follows that it is okay for a plane to BE on the ground at that higher weight, therefore the only consideration is the impact speed with the ground at that higher weight. Since F=MA if you can get your vertical speed to near zero at touchdown you can land a plane at max ramp weight with no damage whatever.
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smartt1982
Topic Author
Posts: 226
Joined: Sat Nov 24, 2007 11:17 pm

RE: Fuel Dumping And Max Landing Weight

Cheers for the info.

How come Boeing have installed the system on aircraft were it is not actually required?. Of course not disageeing or anything but just looked up those FAR requirements that you mentioned and they made mention of a number of aircraft were they have installed a dumping system but it is not actually required.

SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Fuel Dumping And Max Landing Weight

Ah yes, customer options. If you buy an airframe with one set of operating weights you have those limits. If you would like, you can usually "buy" higher gross weights, in the form of performance charts and landing gear/wing spar inspection procedures for that same airplane.

If you start increasing then 25.121(d) may eventually become a limitation on increasing weights, so for a few thousands per tail you can have the pipes and valves installed. Small penalty there - a few pounds of additional weight to carry around but you've removed one potential barrier to operating your plane at higher weights. I'd bet that all models have the possibility (courses for the pipes etc.) designed into them.

It may also make the plane easier to sell, used, to whoever is going to operate it next, when it comes time to replace it with newer equipment. Airlines always have one eye to disposing of their old tails.
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