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777
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Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 1:37 pm

Hi folks,

no later than a 10 days ago I was onboard a DL 767 scheduled on the FCO-ATL route.
The flight had a good LF (>90% IMO) and also on the cargo side I saw a lot of pallets loaded into the belly cargo.

When we started the taxi to the 16R runway the captain told us that we were going to stay on a taxiway for 7-8 minutes and with the engines running quite fast because we were exceeding the MTOW and we should burn rapidly some fuel in order to re-enter in the weight allowance.

So we spent some minutes inside the aircraft (that was shaking due to the power applied to the engines versus the action of the brakes) and then we took off, using the entire lenght of the runway.

After >250 flights I made in my life, this was the first time I have experienced something like that.

Is that a common procedure? How can you get the flight plan released if your weight is higher than the MTOW?
Thanks in advance for any clarification!
 
lowrider
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 1:57 pm

Not common, as you are rarely that close to your Max Ramp weight, but not a big deal either. Most aircraft have a Max Ramp Weight above the Max Takeoff Weight. The Max Ramp Weight is usually MTOW + Standard Taxi Fuel Allowance. This allows you to have a little extra payload. If your taxi time is less than the Standard Taxi Fuel plans for, you will have to burn a little extra off before rolling out onto the runway. I think it has happened to me 5 or 6 times. It can be inconvienient if there is a long line up but that is about the worst of it.
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777
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 2:24 pm

Quoting lowrider (Reply 1):
Not common, as you are rarely that close to your Max Ramp weight, but not a big deal either. Most aircraft have a Max Ramp Weight above the Max Takeoff Weight. The Max Ramp Weight is usually MTOW + Standard Taxi Fuel Allowance. This allows you to have a little extra payload. If your taxi time is less than the Standard Taxi Fuel plans for, you will have to burn a little extra off before rolling out onto the runway. I think it has happened to me 5 or 6 times. It can be inconvienient if there is a long line up but that is about the worst of it.

Thanks for the explaination, I didn't know that there is also a Max Ramp weight!

At FCO if you take off after the early morning rush hour, the taxi time may be actually short and this may explain why an extra time on the ground was needed.
 
26point2
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 3:09 pm

Max ramp weight is a fixed limitation and max takeoff weight varies and can be limited my many factors.

You are talking about only one takeoff weight limit, max structural takeoff weight. There are weight limits to meet max tire speed, required climb and runway length requirements that are considered before every takeoff too.
 
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Starlionblue
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 3:23 pm

Quoting 26point2 (Reply 3):
Max ramp weight is a fixed limitation and max takeoff weight varies and can be limited my many factors.

Could it be, then, that instead of an unexpectedly short taxi there was an unexpected rise in temperature, leading to a decrease in MTOW on that runway length?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Okie
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 3:43 pm

Quoting 777 (Thread starter):
, using the entire lenght of the runway


That would be a No

Mtow is calculated with room to stop from V1.

Okie
 
777
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 4:25 pm

Quoting Starlionblue (Reply 4):
Could it be, then, that instead of an unexpectedly short taxi there was an unexpected rise in temperature, leading to a decrease in MTOW on that runway length?

The temperature was stable as well as the weather conditions, so this should not have been the case
 
Mir
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 4:38 pm

Quoting 777 (Reply 6):
The temperature was stable as well as the weather conditions, so this should not have been the case

While I'm not saying this is what happened, even a rise of two degrees can be enough to push you over the limit for the runway. Not very far, but far enough. Of course, today's jet engines are designed to burn as little fuel as possible, so the (very small) downside to that is that it can take several minutes to burn off enough to overcome even a small overweight situation.

The short taxi time is a more likely scenario. It's a tough thing for the airlines to get right when traffic is busy - you need to have enough fuel to carry out your flight when you take off (obviously), and if that's pushing up against your maximum allowable fuel (in this case limited by MTOW rather than how much you can physically fit in the tanks), you don't have a whole lot of leeway for taxi delays. So putting more on in anticipation of a taxi delay is a good strategic move - you might have to sit and burn some off on the taxiway, but that's better than having to come back to the gate because you're not legal to take off anymore. The infrequence of this sort of thing is testament to how well the airlines are able to do that sort of planning.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
Maverick623
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 6:35 pm

Quoting okie (Reply 5):


That would be a No

Mtow is calculated with room to stop from V1.

Okie

And as you should well know, V1 can often be well separated from Vr in both speed and runway remaining. I routinely see airplanes (usually MD-80s) using up 9000+ feet of a 10500ft runway.
"PHX is Phoenix, PDX is the other city" -777Way
 
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kanban
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 10:16 pm

seems to me this was a thread topic in December...
 
goboeing
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 03, 2011 11:53 pm

Quoting okie (Reply 5):
That would be a No

Mtow is calculated with room to stop from V1.

We weren't there though, so we just don't know.

Last year I had a flight where I just had to start rotating because we were running out of runway fast. My radar altimeter showed 20 feet as we passed over the departure end over the grass.

Point is, there are instances where you really wonder if the thing could even come close to stopping from a couple knots below V1 without going off the end of the runway.

I wish the people who do the engineering behind the takeoff data could be in the jumpseat on the rare occasion where it happens.
 
tdscanuck
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 04, 2011 3:51 am

Quoting GoBoeing (Reply 10):
I wish the people who do the engineering behind the takeoff data could be in the jumpseat on the rare occasion where it happens.

They are. All the takeoff data comes from flight testing.

Tom.
 
goboeing
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 04, 2011 5:39 am

Quoting tdscanuck (Reply 11):
They are. All the takeoff data comes from flight testing.

Let me re-phrase it. There are times when it is apparent that the takeoff data for the conditions and runway is not at all yielding a good result, and passing over the departure end of the runway at 20 feet with both engines running is an example of that. There is absolutely no way we could have done a V1 cut and made it without going into the grass; I refuse to depart that runway under most circumstances after seeing this issue there numerous times.
 
tdscanuck
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 04, 2011 7:30 am

Quoting GoBoeing (Reply 12):
There are times when it is apparent that the takeoff data for the conditions and runway is not at all yielding a good result, and passing over the departure end of the runway at 20 feet with both engines running is an example of that. There is absolutely no way we could have done a V1 cut and made it without going into the grass;

What was the V1-Vr difference in that situation? If they were really close together, the difference in distance to liftoff with or without an engine failure is pretty close.

Tom.
 
goboeing
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 04, 2011 4:24 pm

Quoting tdscanuck (Reply 13):
What was the V1-Vr difference in that situation? If they were really close together, the difference in distance to liftoff with or without an engine failure is pretty close.

I don't remember but since it was a dry runway it would have been the normal spread, which for us is about 5 knots most of the time.

It was not the difference between V1 and Vr that was the problem, it was the fact that we weren't even reaching V1 until 1500' feet of runway remaining.

Now I know 'pedals to the floor' really gets a jet stopped quickly but there is no way we could have gone from 140kts to zero in 1000 feet of pavement. An abort at V1-5 would have been an overrun.

So now it's "unable" and we taxi a bit further to the longer runway, because our takeoff data for this one is clearly bogus.
 
cylw
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 04, 2011 7:43 pm

Could have been that the aircraft was overfuelled and it was quicker to burn off the excess fuel rather than de-fuelling.
 
lowrider
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 04, 2011 7:50 pm

Quoting 26point2 (Reply 3):
You are talking about only one takeoff weight limit, max structural takeoff weight.

In the winter, from FCO, for a 76, that is probably the applicable limit, particularly on a 10 to 11 hour flight.

Quoting GoBoeing (Reply 10):
Last year I had a flight where I just had to start rotating because we were running out of runway fast. My radar altimeter showed 20 feet as we passed over the departure end over the grass.

I see this happen on a pretty routine basis. That is why I think it is foolish to build a runway without overrun areas. Still, I am impressed just how effective max braking can be. I think RTO autobrakes should be standard in all aircraft engaged in 121 pax service. They yield much more consistent accelerate stop numbers.
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golfradio
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Mon Feb 07, 2011 8:47 pm

Off topic, but in the procedure described by the OP, wouldn't the crew have to deal with hot brakes?
CSeries forever. Bring back the old site.
 
lowrider
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Mon Feb 07, 2011 9:03 pm

Quoting golfradio (Reply 17):
wouldn't the crew have to deal with hot brakes

Not unless the brakes were already hot from a long heavy taxi. Modern brakes shouldn't heat that much during a normal taxi.
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planewasted
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Tue Feb 08, 2011 12:04 am

Quoting golfradio (Reply 17):
Off topic, but in the procedure described by the OP, wouldn't the crew have to deal with hot brakes?

Brakes don't get hot when they are locked.
 
747luvr
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 10, 2011 12:25 am

I sat on an old NW a320 back in 2003, capain said the same thing, 'too heavy'. It was only from DTW-FLL, around midnight, 1am before we finally left, and the capt did the same thing, revved them turbines up, you could feel her want to take off, but the brakes held steady...but only time I've ever encountered it.
 
pilotaydin
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 10, 2011 2:20 am

In real world operations, we have two phases of flight...the initial phase we may receive a flight plan and preliminary loadsheet with expected load for the flight, we will enter this stuff in and get an expected takeoff weight. However, we may request extra fuel because of critical weather where we get to and ontop of that, when the final loadsheet comes in, sometimes there are added pax, added loads etc and this may cause us to have a higher than normal weight... MTOW is a number that changes for the actual conditions of the day and airport, Design MTOW is a fixed number. Put these together with a shorter than normal taxi time and there you have it...
I've had to do the same thing with my crew in Hong Kong, we burned off 400 kgs on our A340 to get into takeoff range.
The only time there is too much fuel onboard, is when you're on fire!
 
777
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 10, 2011 10:11 am

Quoting pilotaydin (Reply 21):
In real world operations, we have two phases of flight...the initial phase we may receive a flight plan and preliminary loadsheet with expected load for the flight, we will enter this stuff in and get an expected takeoff weight. However, we may request extra fuel because of critical weather where we get to and ontop of that, when the final loadsheet comes in, sometimes there are added pax, added loads etc and this may cause us to have a higher than normal weight... MTOW is a number that changes for the actual conditions of the day and airport, Design MTOW is a fixed number. Put these together with a shorter than normal taxi time and there you have it...
I've had to do the same thing with my crew in Hong Kong, we burned off 400 kgs on our A340 to get into takeoff range.

Thanks for your contribution, appreciated (as usual)!
 
pilotaydin
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 10, 2011 1:12 pm

Quoting 777 (Reply 22):

very much my pleasure!
The only time there is too much fuel onboard, is when you're on fire!
 
wilco737
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Thu Feb 10, 2011 1:16 pm

When we expect to get around MTOW we don't take the standard taxi fuel (1000 kgs for the 744 for us). We think how close we are to the take off runway and if some delay is expected. Then we decide on the taxi fuel to avoid to burn it away to be in the MTOW range. And if there is some minuntes delay, you are allowed to use the contingency fuel on ground already. Not its original purpose, but allowed.

wilco737
  
 
411A
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 11, 2011 12:59 pm

Quoting Maverick623 (Reply 8):
And as you should well know, V1 can often be well separated from Vr in both speed and runway remaining.

Indeed so.
Recently at JNB, I used nearly all 14,000 feet to get airborne, at max weight.
Happens all the time, worldwide.
 
alwaysontherun
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Sat Feb 12, 2011 12:46 am

Quoting wilco737 (Reply 24):
And if there is some minuntes delay, you are allowed to use the contingency fuel on ground already.

So, in case of a serious delay while waiting for your slot…………you may burn way too much!
Turning around to take fuel will not be appreciated by your company I guess………

Is it common to shut down when it´s obvious that the delay will be severe--> due to whatever reason?
Is it allowed to shut down on the taxiway……..APU only?


###"I´m always on the Run"###
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wilco737
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Sat Feb 12, 2011 9:28 am

Quoting alwaysontherun (Reply 26):
So, in case of a serious delay while waiting for your slot…………you may burn way too much!
Turning around to take fuel will not be appreciated by your company I guess………

If you are at MTOW you cannot really return to the gate and get fuel again. Max is max. We are talking about contingency fuel which is around 3 tons... That is around 15 minutes flight time in a 744. So not too much anyway.
My company says: If you need to return to get the fuel you need, then do it! No complains or nothing! It is OUR decision.

Quoting alwaysontherun (Reply 26):
Is it common to shut down when it´s obvious that the delay will be severe--> due to whatever reason?
Is it allowed to shut down on the taxiway……..APU only?

I had it once at JFK where aircrafts were parked on the runway and shut down its engines and waited until they finally got the release.

wilco737
  
 
474218
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Tue Feb 15, 2011 12:49 am

Quoting 777 (Thread starter):
How can you get the flight plan released if your weight is higher than the MTOW?
Thanks in advance for any clarification!


All aircraft have a Maximum Taxi Weight (MTW). For a large commercial airliner it is normally around 2000 pound over the MTOW.
 
Okie
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Tue Feb 15, 2011 1:30 am

Nothing like running sorties day after day and being so tired and hung over that you do not know if it is Tuesday or Thailand. You inadvertently overlook being 2,000lbs over MTOW with hundred of gallons of high octane and thousands of pounds of incendiaries or that the carb heat is on lumbering down the runway when you get presented with one of those mysteries in life. Will the co-pilot "come to" before the end of the runway and lower the flaps.

Not sure where I read that but it has always stuck in my mind.

Okie

[Edited 2011-02-14 17:31:19]
 
474218
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RE: Burning Fuel During Taxi Due To Exceeded Mtow

Fri Feb 18, 2011 12:41 am

Quoting 777 (Thread starter):
How can you get the flight plan released if your weight is higher than the MTOW?


I ran across this while looking for something else: If you open the "Offical Verdict Investagation Report" and go to page 17 (paragraph 1.6 of the report) you will see that taxing at greater than the MTOW is standard procedure depending of the route and payload.

http://aviation-safety.net/database/record.php?id=19920730-0

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