gilesdavies
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Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 10, 2013 9:45 pm

I was reading about an easyJet flight operating from Gatwick to Bari, that was delayed after the airline had to ask four passengers to leave the flight, due to the aircraft exceeding the Maximum Take Off Weight (MTOW)...
http://www.dailymail.co.uk/news/arti...-journey-hotel-stay-400-Euros.html

I am trying not to dwell on the detail of this story too much, as it is written in newspaper which I cannot stand for their views and editorial inaccuracies. (Just my opinion...) But they do however quote, that an easyJet spokesperson confirmed the flight did exceed the aircrafts MTOW.

This just got me thinking how this was possible and likely causes?

I would suspect the flight was operated by one of easyJet's A319's, while the airline can squeeze 156 passengers on this aircraft, it is only about a 1100 mile flight, so the aircraft would barely be carrying maximum fuel and I highly doubt the weight of cargo would be an issue as a good percentage of easyJet's passengers do not take hold luggage due to them charging extra for this, and this is the only hold cargo they would usually be carrying.

External factors should also not an issue as Gatwick has a 10,000ft runway and the weather in the UK has barely been hot to impede take-off performance.

easyJet operates their aircraft on far longer sectors, which are also fully booked and not heard of this issue before. For example I flew with them Luton to Sharm El Sheikh earlier this year, and the flight was fully booked, and this is a flight twice the distance as LGW-BRI, with a flight time of around 6 hours and Luton's has a far shorter runway of only about 7000ft.

I have not really heard of this issue before, as thought airlines operated their aircraft well within their operational limits, but be interesting to know if this is a common occurrence with other airlines too?

[Edited 2013-09-10 15:10:16]
 
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seabosdca
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RE: Flights Exceeding MTOW. Offloading Is This Common?

Tue Sep 10, 2013 10:09 pm

Three possibilities:

1) Is it actually MLW that's at risk of being exceeded?
2) Are they tankering fuel?
3) Are they carrying more cargo than you think?
 
YYZatcboy
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 10, 2013 11:59 pm

Also is there an MEL limitation? What if one AC pack is inop and they have to fly at 250 the whole way there. That could add up in terms of fuel.
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Starlionblue
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Wed Sep 11, 2013 12:41 am

Quoting gilesdavies (Thread starter):
the aircraft would barely be carrying maximum fuel

Most airliners cannot carry max fuel and max payload at the same time. That would way exceed MTOW.

Quoting gilesdavies (Thread starter):
thought airlines operated their aircraft well within their operational limits

Airliners, especially long-haul ones, often work right at the edge of the envelope for Mass & Balance and Performance. You don't want to waste capacity/performance (and thus money) if you can load some more cargo or take on a bit less fuel. Airlines do keep track of which Captains always take on extra fuel for example.

Note that this is the regulated envelope, so there's quite a bit of safety factor built-in. So you could indeed say that they are well within the actual limits. For example a jet is required to use a runway at least 1.67 times the calculated necessary length for landing (1.92 times if the runway is wet).

Quoting seabosdca (Reply 1):
1) Is it actually MLW that's at risk of being exceeded?

From a Mass and Balance point of view, there are four masses.
- Max Takeoff Mass.
- Max Ramp Mass.
- Max Landing Mass.
- Max Zero Fuel Mass.

From a Performance point of view, there are four limits.
- Field Length Limit.
- Climb Limit.
- Take-off Tyre Speed Limit.
- Take-off Brake Energy Limit.

It gets complicated. 

[Edited 2013-09-10 17:47:48]

[Edited 2013-09-10 17:50:50]
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rfields5421
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Wed Sep 11, 2013 12:48 am

Probably six or seven times between 1999 and 2010, I've 'accepted' an offer to not fly on an aircraft due to weight issues. Most often AA or DL or CO regional jets.

One case at SDF - the AA ERJ135 was weight restricted due to unexpected high temps. Other cases were similar - full aircraft - range - temps, etc.

I always got a nice reward for volunteering. It doesn't happen as much for larger aircraft, but it does upon occasion.
 
FlyHossD
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Wed Sep 11, 2013 3:36 am

Before off loading any passengers, it's alway prudent to count children (a.k.a. "half weights") to be sure that they haven't been counted as adults.

For example, if there were 10 children on board, they weigh approximately the weight of 5 adults.

My former carrier issued memos from time to time reminding crews to take this step - count the children - first.
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MSJYOP28Apilot
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Wed Sep 11, 2013 4:57 am

The A319 isnt exactly the most weight critical aircraft out there. It can be MTOW limited by landing weight but you would need to be tankering a bunch of fuel and have a high bag and cargo count with a full flight. This could easily be rectified by flying lower to burn off the extra fuel.

Knowing EasyJet, I doubt they were carrying tons of extra fuel beyond the minimum required especially if the payload was expected to be high. But if the airline needed to limit how much fuel they uploaded in Bari for whatever reason be it cost or a fuel farm issue in Bari, they may have decided to sacrifice some payload for the extra tanker fuel.

One issue could be a need for a distant alternate if closer selections were not legal to use.

Another could be a NOTAM issued at LGW. If there was a NOTAM for a temporary runway shortening this could degrade the performance numbers and cause a weight issue. If there was a temporary obstacle on takeoff such as a crane this could reduce MTOW based on climb limitation.

There are numerous MELs that restrict performance. EasyJet packs in people on their flights and with a high baggage count being forced to fly a 1100 nm segment at a lower altitude could easily cause MTOW issues.

Bari doesnt have a short runway and isnt at high altitude so I doubt landing distance or landing climb limited weights were an issue.
 
Woodreau
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Wed Sep 11, 2013 9:12 pm

A lot of factors affect MTOW - it's not always structural MTOW.

But airlines usually know in advance what specific flight's MTOW will be and weight restrict the flight prior to boarding so as to avoid offloading cargo or the unpleasant task of offloading people who are already onboard to get an aircraft under MTOW.

Despite knowing the MTOW in advance, sometimes you still go over MTOW even though the plate was weight restricted in advance, and offloading has to be done.

The most common cause I've seen (just in my limited experience) is that the flight isn't long enough distance-wise to burn enough fuel, so the MTOW is limited to the MLW plus the fuel to be burned enroute.

Or the aircraft doesn't have enough performance to takeoff, due to high, hot, or heavy or a combination of the three.

Or the landing surface isn't long enough to dispatch for landing, like at ASE or EYW. It's fine when the runway is dry. But as soon as it "rains" or the runway gets wet, the landing weight is severely curtailed, which will limit max takeoff weight.
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Fabo
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Thu Sep 12, 2013 9:31 pm

Quoting woodreau (Reply 7):
The most common cause I've seen (just in my limited experience) is that the flight isn't long enough distance-wise to burn enough fuel, so the MTOW is limited to the MLW plus the fuel to be burned enroute.

I am not sure what you are getting at. I think I might have a handle on it, but I don't think that particular situation has a lot to do with flight length.

And that is - basically, you have MLW. And then you have MZFW, which is, how much can there be if fuel is not counted. Ideally you want the remaining fuel at destination to be something a bit less then the difference. (it works both ways, when designing an aircraft, you would want the difference to be just a bit more then typical fuel-when-landing, if possible).

It might happen though that you need more fuel at arrival then the difference is (if, for example, you have an alternate that is far away). Apparently you cannot go over MLW when you arrive (lest you want to burn fuel, time and thus money, before actually landing), so if you need extra fuel, you must take from the other side - the payload.
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citationjet
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Fri Sep 13, 2013 2:59 pm

I had a flight delay recently because the plane had to be defueled at the gate. The plane came directly from the hanger with too much fuel on board for the intended flight because of a full passenger load.
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exFWAOONW
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Sun Sep 15, 2013 7:15 pm

One possibility that I haven't seen mentioned (I apologize if I missed it) is they may have had to change to an alternate further away due to poor weather weather closer and had to load more fuel.

Either way, it sounds like defueling is very expensive at that location.
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B777LRF
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 17, 2013 1:17 pm

Quoting MSJYOP28Apilot (Reply 6):
It can be MTOW limited by landing weight

No, it most certainly cannot. See below.

Quoting woodreau (Reply 7):
A lot of factors affect MTOW - it's not always structural MTOW.

Incorrect. MTOW is always a structural limit, and the main deciding factor is engine power (e.g. a 737 with 27K engines will have a higher MTOW than one with 25K ditto, every thing else being equal).



It looks to me like there is some confusion as to the correct terms, so allow me please to clarify:

MTOW - Structural limit, never changes, governed by engine power
MLAW - Structural limit, never changes, governed by landing gear
MZFW - Structural limit, never changes, governed by maximum wing bending

For every single flight a dispatcher or flight crew member will be comparing those three numbers, and by adding various amounts of fuel, will eventually arrive at a MALTOW - Maximum Allowed Take-off Weight. MALTOW may be limited by either MTOW, MLAW or MZFW. Let me provide you with a quick example of how it works.

Say we have a B757, MTOW 100.0 tons and MLAW 90.0 tons. We're taking the bird on a 1 hour flight, trip fuel for which has been calculated at 5.0 tons. Let's say we were to take off at 100.0, burn 5.0, that would see us landing at 95.0, or 5.0 tons over the MLAW. But if we limited the TOW to 95.0, then we won't be too heavy for landing. The 95.0 is called a MALTOW, not a MTOW. This example was just comparing TO and LDG weights, in the real world you also have to compare against the max. zero fuel weight.

But before getting that far a RTOW (Regulated Take-off Weight) will be calculated, which is the weight that takes into account performance objects such as weather, pressure, wind, runway, climb gradient, obstacles etc. If RTOW is lower than MTOW, the RTOW figure will replace the MTOW figure when doing the MTOW/MLAZ/MZFW comparison. The same will happen for MLAW, resulting in a RLAW if applicable. Again, the RLAW will replace the MLAW in the comparison calculation.


As for the case in point, a fair guess is that Ezy had some sort of a performance issue which resulted in a reduction of either MTOW or MLAW, ending in a MALTOW that did not allow carriage of all booked passengers. Nothing unusual about that at all, happens every day several times a day somewhere in the world.
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Goldenshield
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 17, 2013 2:40 pm

Quoting B777LRF (Reply 11):
Incorrect. MTOW is always a structural limit,

Easy, Trigger. He's using MTOW as a generic, all-encompassing acronym for the maximum takeoff weight of the flight, because he's not talking to a pilot; he's talking to someone that has basic idea of how these things work. I understood what he was saying perfectly well.
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Fabo
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 17, 2013 3:23 pm

Quoting B777LRF (Reply 11):

Semantics. FWIW I have often seen using MTOW acronym as your MALTOW, if it was limited by (your) MTOW, the limitation would be marked "structural".

Also I don't think I have seem MLAW, always just MLW (or MLM). Same difference.
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PGNCS
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 17, 2013 3:30 pm

Quoting Fabo (Reply 13):
Quoting B777LRF (Reply 11):
Semantics. FWIW I have often seen using MTOW acronym as your MALTOW, if it was limited by (your) MTOW, the limitation would be marked "structural".

Yeah, exactly Fabo. I have seen numerous performance calculation systems, and there are numerous semantic variables between them. As long as everyone on that certificate (or in a given regulatory scheme) is using their terms correctly what you call anything doesn't matter. I have taught performance and have never once needed the acronym MALTOW.
 
B777LRF
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 17, 2013 5:52 pm

Sorry, I was under the impression this was the technically minded corner of a.net and that usage of the correct terms might be of benefit, particularly to those with little knowledge of the subject.
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Goldenshield
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RE: Flights Exceeding MTOW-Offloading Is This Common?

Tue Sep 17, 2013 6:10 pm

Quoting B777LRF (Reply 15):
Sorry, I was under the impression this was the technically minded corner of a.net and that usage of the correct terms might be of benefit, particularly to those with little knowledge of the subject.

Using correct terms in an appropriate context and then using correct terms because this is how we do it are two different things. Assessing a situation by using the acronyms that you use is fine, but that does not, and should not mean that Woodreau was in any way wrong in what he said because he happened to boil down the situation in way that is both corrolatable to those in the know, and understandable without breaking down all of the nitty-gritty for those who would have to chew on it a while before they understand it.

Think of it this way: When you want insurance, do you call an agent to give you an overview of your situation, or do you call an actuary to break down your risk assessment?

[Edited 2013-09-17 11:15:46]
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