Fuel dump or overweight return?

[rondon9898 84]

Hi folks I was just wondering if there were any guidelines or even rules of thumb about when one would entertain doing an overweight landing following an emergency/malfunction/tricky situation after departure. I know these things are ultimately down to a captin's discretion - they're paid that much to make those decisions - but in real life I only fly little GA aircraft and have no real world experience of operating massive airliners that routinely takeoff massively above MLW. How much over MLW can you be in, say, a 777 or a 747, before you risk gear collapse or other calamity? If you takeoff close to MTOW in the 744 and then a madman in the back starts creating havoc, surely you just have to take the risk of damaging the aircraft/causing injury just to get on the ground ASAP? Or having a fire that you can't extinguish - surely it's time just to get on the ground, no matter how heavy you are? An engine failure with no fire indication/smoke/burning smell (not simulated by PMDG!) I can see would be a relatively calm situation allowing one to take one's time to dump fuel, but what if there had been a fire in the engine that seems to be extinguished? Would you land overweight to get fire crews to inspect the aircraft as quickly as poss, or would you be happy to wait around for ages in the holding pattern dumping the fuel?

Just looking for some opinions/rules of thumb to have in my mind when I fly with my service based failures on. 

[Captain Kevin 586]

If you're on fire, you better get on the ground ASAP. Even with a fire extinguished, you might not necessarily want to be taking chances. Of course, I don't have any real-world experience to back this up, so....

[skelsey 765]

There is another thread running on this here: 

In short - is it time critical? If so then just land it: an overweight landing is not that much of a big deal and you are unlikely to break the aeroplane. 

However, if there is more time then generally speaking it is going to be better to reduce the aircraft's weight. Also consider the type of problem and any potential knock-on effects on braking, landing performance etc - if these are adversely affected then again it would be sensible to reduce weight as much as possible.

For me, any fire is a land ASAP, whether the indication is still on or not: as Kevin says, it's difficult to know whether the fire is definitely out, you don't know the extent of any structural damage that may have occurred as a result etc.

[tcas_climb 45]

A passenger which requires immediate attention that the doctors on board cannot handle might be reason for an overweight landing too.

[scandinavian13 5,192]

6 hours ago, rondon9898 said:

before you risk gear collapse or other calamity?

Granted, this wasn't an overweight landing, but the gear can actually take quite a beating, as this poor Silkway pilot showed us recently:

 

[B777ER 2,483]

Wow, needed a mouth guard for that landing.

[downscc 1,327]

10 hours ago, rondon9898 said:

Or having a fire that you can't extinguish - surely it's time just to get on the ground, no matter how heavy you are?

Several years ago, a Coast Guard Falcon crew had a tail cone fire detector alarm.  Fortunately, they were close by KCRP instead of out on patrol and they immediately landed. Had they been in the air a few minutes longer the tail structure would have failed.  They put in a Signature hanger and took it apart for trucking to their depot, it wasn't going to fly out.  I was hanging around one day and talked to one of the crew and he gave me a tour of the aircraft. The HU-25 is no longer flown by the USCG.

There are few things worse than a fire in an aircraft. Get on the ground.

[rondon9898 84]

Can I just throw a situation to you just to see what you chaps would do - a fault with a demand pump, with the FAULT light remaining on showing there's actually been an overheat situation. It's just after takeoff from EGKK taking about 420 pax to KLAS, very close to MTOW. For a landing below MLW you'd need a significant amount of fuel dumping, so you'd be in the hold for ages. Land close to MTOW or dump in that situation? 

[Captain Kevin 586]

The QRH does say plan to land at the nearest suitable airport, and it also lists the systems that go out when you have certain hydraulics systems inoperative. The question then is how much control do you have of the plane. Bear in mind that with certain systems out, stopping the plane on the runway might be an issue, so you may be better off dumping fuel at that point.

[skelsey 765]

Personally I'd dump the fuel in the absence of any other indications. What specific fault/failure are you thinking of? There's a big difference between HYD PRESS DEM 1, 2, 3, 4 and HYD OVHT SYS 1, 2, 3, 4.

TDODAR is a useful decision making tool:

Time -- plenty of gas (obviously!), aeroplane's flying fine, no fire, nothing else particularly limiting time wise.

Diagnose the problem - you say it's an issue with the demand pump -- obviously the impact will depend on which specific system it is but fundamentally the 747 has an awful lot of hydraulic redundancy and a single demand pump failure is pretty close to a non-issue.

Options - essentially these are: 1) continue to destination 2) return immediately to LGW and land overweight, or 3) dump fuel and return to land at LGW below MLW.

Option 1) -- well, if we assume LGW is home base then it's probably best to return there on the basis of engineering support. If it's just a demand pump though then it's not completely out of the question to continue -- it does depend which one though (1 and 4 would be a problem as there are quite severe TOPL restrictions which would likely preclude a return flight, whereas 2 and 3 are less critical). So we'll assume we're going to return.

2) - Return immediately and land overweight. What are the benefits? We get on the ground quicker, but is there any particular urgency to do so? This expediency should be weighed against the much higher than usual approach speeds that will be necessary resulting in an unusual landing anyway on top of any secondary issues. The brakes and tyres will end up very warm indeed and the risk of a runway excursion in general is increased. Plus we'll need to add an overweight landing inspection to the engineering actions. Is it worth it?

3) Dump the fuel and return to LGW -- it'll take longer to get on the ground but we'll be flying more sensible speeds with less stress on the aeroplane all round - flaps, tyres, brakes etc. The stopping distance will be less and there'll be no need for an additional overweight landing inspection.

Decision - no brainer for me -- 3), dump the fuel and get below MLW. Of course, we can always monitor the situation and if anything changes we can simply stop dumping and make an immediate approach if we decide for any reason we need to get on the ground ASAP.

Act/assign tasks -- any QRH tasks remaining, liase with ATC and the cabin, reprogram the FMC for a return etc etc.

Review -- as mentioned above, you're going to continually review the situation, check for anything you might have missed etc.

Others may have a different view but for me -- take your time, dump the fuel (assuming takeoff at MTOW of 397 tonnes and an MLW of 285 tonnes you're looking at circa 110 tonnes to dump -- the rule of thumb is tonnes to dump/2 + 10 minutes, so about 65 minutes to get to MLW) and give yourself a nice unhurried, normal landing.

[AirbusCG 52]

1 hour ago, Captain Kevin said:

The QRH does say plan to land at the nearest suitable airport,

Note that "land at the nearest suitable airport" is not the same as "land as soon as possible".

In fact the nearest suitable airport must not necessarily be the nearest airport that is able to accept/handle a 747. It could be an airport that is some flying hours away, for example your homebase with a maintenance facility, assuming you have no maintenance contracts at the nearest 10 airports with 4km+ runways.

All in all I'm fully with Simons TDODAR above, I'd also go for the fuel dumping followed by the return to LGW.

[Captain_Al 66]

If you have something like a cargo fire after takeoff and climbing out on the departure at maximum takeoff weight, the 747 landing gear is built and stress tested to land up to the maximum takeoff weight. Particular attention has to be given to runway length, winds, descent rate at touchdown, and flying a stabilized approach, but the aircraft does just fine in this situation. You will land with Flaps 25 using VREF 25 since you get Flap Load relief if using Flaps 30 at the higher weight. This is a scenario we do in FFS training on the 400. Of course, inspections would then be required.

[Captain Kevin 586]

5 hours ago, Emi said:

Note that "land at the nearest suitable airport" is not the same as "land as soon as possible".

In fact the nearest suitable airport must not necessarily be the nearest airport that is able to accept/handle a 747. It could be an airport that is some flying hours away, for example your homebase with a maintenance facility, assuming you have no maintenance contracts at the nearest 10 airports with 4km+ runways.

I'm aware of that. I never said anything about landing as soon as possible. I just quoted the QRH. In fact, with a hydraulics pump out rendering some systems inoperative, landing as soon as possible would be a bad idea, given the weight of the plane for that particular flight and the limited control of the plane. At that point, I would dump fuel even below maximum landing weight.

[rondon9898 84]

13 hours ago, skelsey said:

Personally I'd dump the fuel in the absence of any other indications. What specific fault/failure are you thinking of? There's a big difference between HYD PRESS DEM 1, 2, 3, 4 and HYD OVHT SYS 1, 2, 3, 4.

[rondon9898 84]

1 minute ago, rondon9898 said:

13 hours ago, skelsey said:

Personally I'd dump the fuel in the absence of any other indications. What specific fault/failure are you thinking of? There's a big difference between HYD PRESS DEM 1, 2, 3, 4 and HYD OVHT SYS 1, 2, 3, 4.

Actually, Simon, I got a bit confused in my post sorry - I meant there was a system overheat, as I'm aware a failure of a demand pump wouldn't be critical. Would your reply change in that case?