rondon9898

Fuel dump or overweight return?

Recommended Posts

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. 

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

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....

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites
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:

 

  • Upvote 1

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

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? 

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites
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?

Share this post


Link to post
Share on other sites
12 hours ago, rondon9898 said:

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?

No worries. I don't think it would -- again, the only advantage of an overweight landing is that it gets you on the ground quicker, but at the expense of more stress on the airframe than a landing below MLW and at an increased risk of hot brakes, runway excursion etc etc. Is it worth it?

It's not quite the same, but in a sense you could liken it to a high-speed RTO. The aircraft is certified for it, your performance calculations tell you that you can stop safely at any speed up to V1, but even so the stats show that high speed RTOs are inherently risky and frequently result in runway excursions and other problems. Thus, the takeoff roll is divided in to a low-speed portion where you consider stopping for anything, and a high-speed portion above 80 knots where you only stop for a limited number of certain clearly defined reasons - i.e. not because it is possible to stop, but because the aeroplane will not fly. This is because apart from these few critical scenarios, the risk of stopping is greater than the risk involved in solving the problem in the air.

You could look at an overweight landing in the same way. Is the risk of an overweight landing with all that extra energy (remember: E = 1/2mv^2 and in an overweight landing you are making both m and v significantly bigger) greater or less than the risk of staying airborne for an extra hour or so?

In almost all circumstances, I would generally suggest that it is going to be better to dump the fuel and land below MLW.

Share this post


Link to post
Share on other sites

Got you thank you very much for those responses Simon - gives me a bit more context to work with in realistic decision making in the sim

Share this post


Link to post
Share on other sites

John,

Assuming you are already airborne, one of the first actions you must take when dealing with an overheat in one of the hydraulic systems is select a serviceable autopilot (Hyds 1,2 3, control A/Ps C,R,L respectively) .  The QRH actions should be carried out methodically and slowly because it can take a little while for the HYD OVHT SYS message to go out if the Demand Pump and/or the Engine Pump is at fault. If you end up switching both of these pumps OFF on the affected system then the QRH instructs you to initially ignore the HYD PRESS SYS message at this stage (for obvious reasons).  Please note that the B744 QRH definitely does NOT require you to dump or land at the nearest sutiable airfiled in this situation!

The aircraft is capable of flying perfectly well with three hydraulic systems and line crews are regularly trained and tested on their ability to fly with only two. Therefore, there is no need to panic in this situation because you have only lost one of your four hydraulic systems.  Unless there is another more serious problem (such as an uncontrollable cargo/fuselage fire) why would you want to dump fuel or divert from your original flight plan?  An uncontrollable fuselage fire is of course one of the worst things to experience in flight and I would certainly aim to get the aircraft back on the ground as quickly and as safely as possible in this condition - and I definitely wouldn't waste time or dump fuel with the aircraft on fire because it takes over an hour to dump from MTOW to MLW on a B744.  However, the fault in the hydraulic system might have been caused by a simple leak and loss which has eventually resulted in the overheat, in which case there might be a sufficient amount of fluid left after completing the QRH to allow you to turn the pumps on momentarily to lower the flaps and/or gear by the normal system prior to landing at your destination.

You should always plan for the worst case scenario and (as Simon has pointed out) when time permits DODARing the problem is always recommended. This should always include thinking about and planning for the approach, landing and possible go-around and diversion.  Carrying out the Hydraulic Overheat System QRH procedure may result in you having to carry out the HYD PRESS SYS checklist.  Even if you haven't totally lost the hydraulic system it is always sensible to have a look at what effect this will have on the operation if you subsequently lose it later on in the flight.  ATC will need to know and they are there to help you.  If the weather is below CAT 1 you will have to divert because CAT 2 & 3 autolands are not approved with any loss of a single hydraulic system.  A loss of hydraulic systems 1 and/or 4 have the biggest impact on the operation and you will also need to consider such things as the operation in icing conditions, the length of the runway, stopping distance, cabin pressurisation, spoiler operation etc  The list goes on!

Happy landings if you try this as a scenario!

Bertie Goddard       

  

    

  

 

 

     

Share this post


Link to post
Share on other sites

John,

From a certification perspective, any part 25 airplane must be structurally capable of safe landing at maximum certificated takeoff weight. I believe the assume touchdown rate is 6 FPS or 480 FPM at MCTW, but I would need to check part 25 just to be sure. Any part 25 airplane that cannot meets its OEI approach and AEO landing climb limit weight 15 minutes after takeoff from any airport within its permitted operating takeoff airport envelope must have fuel dump system.  However, it is not required that the pilot dump fuel in an emergency to bring the airplane down to its maximum weight where OEI approach and AEO landing climb are met .  That's a Captain's discretion item.

On a four-engine airplane, the PIC has the option to continue the flight. It's an old, somewhat archaic rule that dates back to the Constellation and DC-7 days where engine failure were quite common.  A few years back a British Airways Captain got into hot water with the FAA after they experienced and engine failure on takeoff during climb out of LAX and elected, legally, to continue to EGLL on three engines. The FAA conceded that the rules allowed the pilot to do that, but also asked BA to ensure that their crews didn't do that again in US airspace as it was always intended for oceanic operations particularly departing from remote airports.  There's a part 91 rule that requires the PIC to discontinue the flight anytime a mechanical problem affecting airworthiness, but the other rule regarding an engine failure on a four engine airplane created a grey area.

Notwithstanding an emergency, the PIC must ensure that the airplane is below maximum certificated landing weight in the event of a landing at an airport other than the planned destination (e.g., return to departure airport). For example, if the IRUs were not properly aligned prior to takeoff (no GPS) and there was need to return to the departure airport to re-align the IRUs, then fuel dumping to the MCLW would be legally required.  If the airworthiness of the aircraft is in question, then fuel dumping is not necessary as the PIC is using their emergency authority.  The QRH usually uses terminology like "Land as soon as possible" or "land at nearest suitable airport" to assist the PIC in assessing the need to terminate the flight using this authority. Some QRHs use the term "land as soon practical" to give the pilot greater leeway in making a decision to land.

Outside of performance considerations provided in the AFM or QRH, overweight landings are generally a maintenance function. Inspections will vary depending on the rate of touchdown. if greater than 3 FPS/360 FPM, then the inspection becomes greater.  Most modern airplanes have downloadable information that provides both the weight at touchdown and the touchdown rate.

Hope that this helped,

Rich Boll

Wichita KS

Share this post


Link to post
Share on other sites
On April 24, 2017 at 9:10 AM, scandinavian13 said:

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

 

Kyle, equivalent flap shock animations would be greatly appreciated in the next update. Hahaha

On a serious note for those with RW knowledge, are mandatory inspections required and what do they involve following a landing such as this? How long would these keep the aircraft out of service?

Share this post


Link to post
Share on other sites

John, et al,

In the sim community- folks have traditionally misunderstood what your MLW really means.

If you land at a weight that exceeds your MLW, It does NOT mean that the airplane will break.  To the contrary- airplanes touch down over MLW with relatively little fanfare.

The MLW is a weight that is established by the manufacturer's engineers as the weight at which the structure of the airplane will continue to lead a normal structural lifespan.

If you bought yourself a 777, and landed it 100,000lbs over MLW every single time you flew, that airplane would theoretically show signs of fatigue wearing at a rate faster than an exactly identical 777 that was routinely landed at a lesser weight.

Makes sense, right?

So from my vantage point on the flight deck- if I take off at 877,000lbs and and have a catastrophic failure that calls into question the safety of the airplane or it's occupants- I am going to make the decision to eat some of the stress life of the airplane by putting it back onto nearest, most suitable runway available.

If, on the other hand, the biggest risk to the flight is that I might inconvenience my passengers schedule, I will take the time to find someplace reasonable to dump fuel and reduce weight.

There are even occasions where the airline might decide it is necessary for me to return to the field- and they will make the decision to authorize an overweight landing pending the crew's agreement...  it all takes place within the sphere of the modern airline operation.

What happens after a landing over MLW?  The manufacturer has provided the airline with a detailed inspection to put the airplane through, depending upon the circumstances.

All in a day's work.

 

Share this post


Link to post
Share on other sites

As Robert points out, its not gonna break. Some airplanes actually have different MLW options the airline can purchase, with the higher MLW options costing more in both dollars and airframe life.

Freighters often have a much higher MLW to carry more payload with less range (trading fuel for cargo) and are also operated on a less intense schedule than most passenger frames, evening out the increased wear, somewhat.

Point is, in a fire, or serious emergency, get it on the ground ASAP

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now