Now, I know perfectly well that the literal and unhelpful answer to the question is long enough to burn sufficient fuel that it is no longer overweight for landing. What I'd like to understand is whether it is possible or not to give an answer about what's typical.

I am surprised that after flying all the way from Moscow to Ireland this aircraft had enough fuel on board to be still overweight (even given that it still had to go all the way to the Dominican Republic):

An Azur Air Boeing 767-300, registration VP-BUX performing flight ZF-973 from Moscow Vnukovo (Russia) to La Romana (Dominican Republic), was enroute at FL320 about 90nm south of Shannon (Ireland) when the crew decided to divert to Shannon reporting all their lavatories were blocked. The aircraft dumped fuel and landed safely on Shannon's runway 24 about 90 minutes later.

Typically, how much of an airliner's flight will be in an overweight-for-landing condition?

Does it vary so much between aircraft types, distances, passenger/cargo weights and other conditions that it's not simply possible to say what is typical, or is it possible to say that the case above is (for example) unusual?

  • $\begingroup$ It depends on many factor, including if the aircraft is doing tankering (i.e. flying with enough fuel to not needing refueling between legs) $\endgroup$ – Manu H Jan 13 '19 at 14:31
  • $\begingroup$ This question is too broad. For example, the 757's MLW and MTOW are closer than on most other aircraft, meaning that it can land much sooner after take-off even with full payload and full fuel. $\endgroup$ – DeepSpace Jan 13 '19 at 14:35
  • $\begingroup$ @DeepSpace That would be part of an answer - I allow in the question that it might not be fully answerable. $\endgroup$ – Daniele Procida Jan 13 '19 at 17:04
  • $\begingroup$ As asked, this question is only answerable with a huge "it depends". With a light passenger load & a short flight, it's perfectly common to take off well below the max landing weight. With a full load & lots of fuel, it may be close to the destination before you're down to max landing weight. With enough tailwinds & shortcuts, you may arrive at the destination a few hundred pounds above max landing weight (which is generally solved with burning, rather than dumping, the fuel). But "how long" will it take? It just depends. $\endgroup$ – Ralph J Jan 13 '19 at 19:45

Unless you're asking for a very specific aircraft in a well defined situation, the answer has to be some distance, as there is a multitude of factors involved.

This list is more of a rough collection than anywhere near complete.

  • First off, if it started with a load already below Maximum Landing Weight (MLW), then no dump is needed. This isn't that unusual, as not every flight is fully loaded - even with tanks full.

  • Next, MLW is not an absolute value in real life situations, it's a requirement for flight planing

  • Pilots can decide to land, within reason, with a weight past MLW

  • The ability to land on a certain Airport depends on the runway length available.

  • Weight is a combination of fuel tanked and passenger/cargo load, so

    • With low load, tanks can be full a safe landing can be done without dumping

    • Similar, with a loaded plane and a partial filled tank (like on short hops)

    • Or a combination of both, like a series of short hops without taking fuel.

  • The difference between Maximum Take Off Weight (MTOW) and MLW differs drastic between planes for some it's even the same

  • There are different fueling strategies depending on airline and destinations. For a large airliner diference in fuel price can easy accumulate to 30 grand or more.

    • On international flights fuel price at the destination may be so high compared to the origin that it saves money to fly in with tanks filled up to minimize the amount of fuel to be taken at destination for the flight back. Thus even for a shot distance flight tanks may be all filled up (or at least as much that the planned landing will still work out)

    • If fuel at destination is comparable (or cheaper), the flight may be done with the minimum fuel necessary.

    • Same if fuel at the destination is quite cheap, the captain will be ordered to tank as much as possible to return safe.

    • A plane doing many short hops over a day may load (at some point(s)) as much as possible to reduce time needed for refuelling and increase time flying

  • Pilots will always try to avoid dumping, as it's literally throwing money out the drain.

... And so on. As said before, there is an almost unlimited number of factors that define the amount of fuel on a plane, its relation to cargo and if a landing with the resulting weight is safe or not. Only if all of these factors add up to the not possible side a dump is to be done.

Angela Merkels failed flight to Argentina in November 2018 makes an interesting example for an extrem combination. The Bundeswehr long haul A340-300E was fully tanked for a ~7,000 nm flight, but still way below MTOW due the light cargo. When the radio failure was detected an hour after start (from Berlin), it returned to Cologne. EDDK got a well sized, almost 4 km long runway, leaving ample space for an overweight landing.


Does it vary so much between aircraft types, distances, passenger/cargo weights and other conditions that it's not simply possible to say what is typical

This is pretty much the case. For example in a lot of smaller trainer aircraft you are more or less always in the CG range to make a successful landing. On the contrary in larger aircraft fuel burn schedules are extremely important to simply keeping the aircraft airborne.

Dumping fuel is generally not idea from a strictly business standpoint you are basically throwing money out of the aircraft which no airline wants to do on purpose.

What varies heavily between all flights is that at some point its up to humans, and humans make mistakes. Fuel loads may be calculated automatically but some guy still needs to usually shut the pump off at the right time, the pilots need to fly the plane as prescribed and the conditions need to be as expected. Any variable in this could create an issue for you.

For example lets say you take off and get an unexpected tail wind of 100 Kts for the whole ride. Lets also say that you loaded up as much fuel as you could on account of you were flying to a smaller airfield and you were unsure they had enough fuel on hand to get you home. You knew you could bring enough to get there and back but you would be right at the limit of the load config. That 100Kt tail wind is going to save you a fair bit of fuel you intended on burning and due to unforeseen things you may now be over weight.

Now lets say you are flying short haul in a 737, you are doing a 30 min hop and its the end of the day. You have the the required fuel plus reserves so you are flying pretty light. A light passenger load and not much cargo to haul, you may be in range for the whole flight.

Those are just two of a very long list of examples of different load configurations that can lead to always in range, or substantially out of range situations.


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