Interesting explanation, but not entirely satisfying. For example, what happens with all those long flights that get diverted shortly after takeoff due to MX, medical, etc.? Somehow they all manage to land without incident. I guess there are "exceptions" to the rules depending on the problem, but there is no exception made when you know in advance that your fuel load will be higher than usual on landing .

Okay, I see that. Turns out I quoted the wrong number...

However, that said:

From Wiki on Overall Pressure Ratio (yeah, I know, bad source. I'm limited on time here.)

So, perhaps today's modern engines are approaching compression ratios that of pistons---at least the incoming air is, but not the fuel.

So they were loaded above maximum recommended landing weight?

They may not have taken off above the maximum landing weight, for one. Or they burn the fuel off before landing, or dump the fuel in the air (obviously, airlines don't want to waste fuel except in those emergencies). And landing above the max weight requires all sorts of (costly) maintenance afterwards. That's why they don't make exceptions when you know in advance that you're overweight for landing.

They dump fuel or circle around to burn it off.

Typically, swaps like this happen at outstations due to maintenance issues particularly MEL items you dont want or cant legally have on a flight from PDX-IAD. The equipment router that makes the swap is supposed to verify the fuel on board so the dispatcher can run the fuel numbers to see what kind of weight issues might result. If it was a last minute change or the coordinator forgot to obtain the fuel on board, it can come as a surprise to the flight crew to find so much gas onboard and make the possible delay worse for de-fueling.

De-fueling is not always the best solution. There are a limited number of de-fuelers and fuelers already have a pretty tight fueling schedule. Like airlines, fuelers dont leave trucks and crews just sitting around. Once de-fueled, the gas is considered contaminated and is essentially worthless for another flight.

The main weight issue would be max landing weight. You are not allowed to in normal operations land above the max landing weight. The only type of overweight landings allowed are those when you have an issue that requires an immediate landing. Each airline has an overweight landing procedure for each type that it operates. Occasionally in some types, flights may inadvertently land a little above max landing weight. Before an inspection needs to take place, it needs to be a landing a certain amount above the max landing weight usually. That is determined by the manufacturer and the airline.

It is legal to take off with a fuel and passenger weight that would exceed max landing weight at landing so long as enough fuel would be burnt off enroute to meet the landing weight limitation. That would mean either having the dispatcher file a longer flight plan, flying faster, lower, dropping the gear and flaps early, or going into a holding pattern to burn off the gas. This can take a long time to do depending on how much gas needs to be burned.

Burning fuel on the ground is normally the easiest way to burn off excess fuel in all cases of weight limitations. I am not sure how much fuel needed to be offloaded equated into time sitting in the run up area burning it off.

Occasionally, bumping passengers and bags may be easier and quicker or even operationally better than taking long delays burning off gas or de-fueling.

De-fueling is typically used for max landing weight situations when burning it off in taxi would take too long, ATC wouldnt allow a longer flight plan due to traffic patterns or the captain and dispatcher didnt want to fly a longer flight plan. A lot of reasons go into the decision to de-fuel instead of burn off gas another way.

Normally, this is a decision between the captain and dispatcher. It depends on downline flights, crew duty limitations, and judgment calls between the captain and dispatcher.

For de-fueling, it technically isnt something the captain and dispatcher need to agree on but if the captain on his own decides to de-fuel and it takes a long delay, he can easily get tagged for the delay.

From what Ive seen and have heard about the B757, 9,000 lbs doesnt seem like a ton of fuel for that type. I wonder why flying lower wouldnt have been easier than waiting for de-fueling. Looking at Flightaware, the B757 flying UAL294 on 05/17 was filed at FL350. For 9,000 lbs of gas, flying in the FL200-FL300 range should have taken care of a 9,000 lbs difference on a B757 I would think and save more time as well.

I'd be surprised if any airline would not require an inspection on any overweight landing. The max is the max, and if we land heavier than the max landing weight, at least at L-UAL, it's required. That's obviously not to say that you cannot land heavy, just that an inspection is required if you do. Some airplanes have fuel dump capability, others don't. The 757-200s don't, same with 737 and A-320/319. 767s can dump fuel. There are others, but I'm staying with the planes I've flown only here.

9,000 lb of fuel is a little over an hour of cruise flight time, so it would be close to impossible to overburn that much on a two hour flight, even at very low altitude. The right altitude is a big deal in the overall fuel efficiency, but not that much. The flight in question may not have had to off load or burn the whole 9,000 though. If I needed to get rid of only 2,000 to be legal but we were overfueled by 9,000, I'd have had them take all 9,000 off since its not much more time once the defueling process is underway.

FAB

if I may, I will put some $ perspective in this conversation... typical fuel density is between 6.68 & 6.8 depending on weather and if it's in the fuel farms or in the tanker for a long time.. jet fuel is roughly same amount at the typical gas pump or higher, dependent on hedging contracts and price per a barrel... let's take for instance my home city CLE... gas at the pump is averaging 3.85 at the moment, and let's say UAL contracted for a significant fuel hedge contract to reduce the price per a barrel of refined jet-a to a "mere" 3.45 a gallon and the daily fuel density was 6.7... 9000 lbs of fuel would be roughly 1340 gallons... multiply by price per a gallon and it comes close to $4500... (again speculation and hypothetical but a useful example) now it's up to dispatch and captain to figure out which is more cost effective... but I do think without a doubt if mother company head honchos don't want to burn $4500 everytime things like this happen when it would cost less to reroute and accomodate misconnect passengers if such the situation arrived every time... figure average hotel and meal per a passenger needing it off such a delayed flight was $145 max (ish) and not every passenger off an average 737-800 (that's 154 max... which seems to be average flight load fleet wide from the 319 to the 747)... if maybe half the passengers need the hotel/meal combo, we're looking at 77 passengers at $145, it's only coming out to roughly $1400 compared to the $4500 of wasted fuel... for the business folks out there, losing the $1400 is the better cost effective option for a delayed flight than the $4500 of just unnecessarily wated resources... but those are my $.02...
-Cle-

Max Takeoff Weight
 

Early 1990's we were flying home LAS-YYZ on an Air Canada B727. That July day the temperature was over 105F and the flight was very full. Just before the door was closed, five late arriving passengers boarded and shortly afterwards the captain announced that because of the late arrivals, they had to recalculate the weight for takeoff and we needed to remove some fuel before starting. About 45 minutes later, after we had been defueled at the gate, we taxied out and did a "standing start" (remember them, pilot stands on the brakes while the engines are spooled up quickly before the brakes are released) and we started rolling along a 12,000+ foot runway. Looking out, I remember seeing the 10,000 foot marker pass, then the 11,000 foot marker, and as we approched the 12,000 foot marker the aircraft shuddered as it lifted off slowly. We then made a right turn and circled inside the bowl of hills that surrounds LV for three complete circuits before we were high enough to clear them and continue northeast toward Toronto. I don't think we'd have made that takeoff safely if the flightdeck hadn't recalculated to remove some fuel because of the late arrivng pax and their luggage.

bj-21.

CleUnited, 77 @ $145 is $11,000, not $1400.. If your passenger estimate is accurate, the defueling is much cheaper.

w yeah you're right... couldn't do math last night... long day dealing with a gate return CLE ORD double gate return yesterday... of course usually, it's not $145 and the passenger estimate is really not correct... just assuming... but I was saying just to put some money I dea out there... typically it's just 35 ish rooms closer to $60 per room plus meal vouchers which is usually $20... but I was aiming at high estimates... thanks for the double check on my math...

-Cle-

Btw- new numbers assuming same 77 passengers need rooms but we only delve out 35 rooms plus meals for everyone... comes to $3640

Reminds me of a flight I did on a C-172 with two other pax and luggage out of VGT (North Las Vegas) in 1999, at @ 110 degrees F. Though you forgot the wind shear. :p

Or the captain uses his emergency authority to land over max landing weight. Takes a while to burn off a lot of excess fuel, even configured.

AD

Regardless of type, 9,000 lbs sounds like 4.5 tons. ;)

Last December, we were heading for Berlin, via Newark and then London. We had about 95 minutes in London, which wasn't a lot considering Newark flights go into terminal 5 and LH goes out of terminal 1. We boarded, and were ready to go, with a planned arrival of 55 minutes early. Pilot announces the plane was originally going to go to Asia, so they had to offload fuel. I think it took almost 45 minutes for the truck to even show up.

We left about an hour late, and I think we had about 1 hour to make the flight. Then, just before we landed in London, my husband looked at his paperwork, and realized that he didn't have a boarding pass for LH, just a departure management card. (I checked in at the airport and did, he'd checked in earlier at home).

Ran to the bus, ran through the terminals, waited for security, cut into the LH line and got to the gate about 14 minutes before takeoff. They hadn't even opened the gate area, so we made it. (Hubby never did get a boarding pass, they just boarded him when he asked for it at the gate). Pilot tells us that in 16 years of flying that route, he's left on time once. Sigh.