How do airlines plan their payload for multiple flights in a day?

Question

Of course, this isn't specific to a single airline or airplane. As a base rule, it is needless to say that airlines want to profit as much as they can and the payload is a strong factor to influence the profits.

That said, let's take an example of a B737 of ABC Airlines that will be making stops to 3 different destinations before reaching its final destination.

Assuming 2 of the 4 legs have sold all seats, while the other 2 have sold only half:

1. How will the fuel on-board be planned? Will it benefit to carry enough for 2 legs so that they spend the least amount of time at the stop-over?
2. Will it benefit to only have the required fuel for one leg (including the reserves and alternate), and thence allow more luggage from passengers which would otherwise be declined?
3. Are these decisions made by dispatchers, pilots or a different department? Are they made right before each flight or pre-planned well in advanced?

I'm asking these because I want to understand how airlines plan their flights as to, you guessed it, maximize profits while still maintain inflation schedules and passenger satisfaction.

Answer 1

The only real answer we can give to this is it depends

It depends on the airline, the nature of the legs (long/short), the specific airports/countries involved (re-fuelling costs can vary significantly) and route profiles used.

If the aircraft is doing 4 very short legs, the cost of carrying the fuel may be less than the cost of refuelling three times. Equally it's certainly faster to fill the plane once, rather than 1/4 fill it 4 times, because so much time is spent in setting up etc, and you can't usually re-fuel with passengers on board.

On the other hand, if legs 1 and 3 are nearly at the endurance of the aircraft, you physically can't carry fuel for legs 2 and 4: your fuel tanks aren't big enough. Equally on longer routes, the cost of carrying extra fuel increases dramatically.

Flip that around and say that legs 1 and 3 are short, but legs 2 and 4 are long (without being at the aircraft's endurance) and you have a problem that during legs 1 and 3 you're carrying a lot of un-neccessary fuel.

All airlines will have different policies and procedures, and those policies will vary wildly depending on the fuel costs at different airports. But I'll try to summarise at least some of the options here

• For lots of short routes, fuelling once for multiple legs can be viable, but may not be the best option depending on fuel costs at each location. You wouldn't necessarily do a full day on one re-fuelling instance, but you may fuel twice for 4 legs, for example
• For a short leg followed by a long one, it's rarer but the above will still reply
• For a long leg followed by a short one, it's unlikely to be cost effective, although in certain situations your second leg's fuel load could be close to the reserve needed for the first leg: as long as you don't have to eat into your reserve on the first leg, you don't necessarily need to refuel.
• For multiple long legs, you almost certainly don't have the fuel capacity, and carrying so much extra fuel for so long makes little sense: that's expensive.

In short, you usually want to fly with as little fuel as possible - a light aircraft is cheaper to run, can hold more cargo/luggage etc.

In a few situations, the cost of refuelling can make it worthwhile to fuel up in one location, where the cost of fuelling there makes up for the cost of carrying that extra fuel around. That's a niche scenario though, and wouldn't be the "usual" mode of operation for most airlines

Answer 2

Question number 3 is the only one that can be answered without involving too many unknown variables.

The final responsibility lies with the crew and particularly the commander or captain on a particular flight. The crew's job is to make sure that a) regulatory requirements are met and b) that commercial interests are considered, in that order. A third component is common sense, airmanship or whatever you want to call it, which aims to make sure that the mission is accomplished with a reasonable margin to minimum requirements.

The answer to question 1 and 2 depends on a range of factors:

• Fuel price at the various ports of call (is fuel even available everywhere?).
• Other fuel related restrictions at various airports. In some places passenger boarding is not allowed during fuelling, which slows down the whole process.
• Weather conditions at each stop.
• Landing and take off weight restrictions depending on runway conditions and performance requirements due to runway length or terrain around the airport.
• The cost of time vs fuel burn. How expensive is additional fuel burn in comparison with aircraft leasing costs, engine maintenance and crew salary? There might be cases where a set of flights can't even be legally assigned to the same crew unless they are completed within a certain time frame due to duty time restrictions.

All of these factors lie mainly within the responsibilities of management and long term planning staff.

In practice this all works out so that a crew checks in for a duty and receives a plan for the flights of the day, including a suggested fuel figures and fuel strategy. The crew then accepts the plan as it is or makes required adjustments to it. Again, this procedure varies from airline to airline. In some airline the preparation work is done by designated staff, while other airlines might rely more on computer generated plans, which of course leaves a larger share of the responsibility with the crew.