How many calculations of W&B and fuel burn?

[AnthonyGA]

I know that the FMS aboard large transport aircraft calculates fuel burn and some limited weight and balance figures, but does anyone else duplicate them?

In other words, do pilots routinely calculate fuel burn and W&B manually, in addition to the FMS? What about dispatchers? Are there computers back at the airline's headquarters that duplicate the calculations for back-up?

On the one hand, it seems prudent to calculate these things more than once in different ways to make sure they are right. But on the other hand, a manual calculation by a human being is actually more likely to be in error than a computer calculation (once the computer's software is fully debugged), so it would seem to be a waste of time.

So what calculations, if any, do the pilots, dispatchers, or other parties still do prior to a flight?

[polarbearjim]

The dispatcher would use a computerised system, sometimes the same system used for check in, to create a computerised loadsheet. The weights and c.g. positions for the empty aircraft are stored in this system and the effects of passengers, cargo and fuel are calculated to find the new weights and c.g. positions for the zero fuel, take off and landing cases. The weights used are normally standard weights which would have come from a statistical survey of passengers.

The fuel figures inputed into the loadsheet would include the fuel the aircraft is loaded with on stand, the fuel burnt during taxi and the fuel burnt during the flight. This information would usually come from a flight plan created by the airlines operations department. They would most likely use a computer system to calculate this but it can be done manually with performance tables for the aircraft and the pilots could of course create their own but having others do it saves time and makes the pilots lifes easier. The flight plan data would have been calculated using expected weights which might change so the pilots might change the fuel figures from that calculated by the flight planners. This might also be done for other reasons for example weather.

Once the crew have a loadsheet they will take data from it and input that into their flight management system. This allows performance data to be calculated, for example the takeoff speeds and optimum cruise altitutes. Some aircraft for example the A310 can pump fuel into trim tanks to bring their c.g. position to the optimum so having an accurate loadsheet is very important if this capabiltity is to be used.

A loadsheet can also be completed manually by the dispatcher or the pilots if there is no computer system avalibable. It is usually checked by the dispatcher, possibly their supervisor and again by the crew for errors. It is usually part of the dispatchers job to make sure the aircraft is loaded the way the loadsheet says it is.

The crew will have a fuel monitoring procedure to make sure the flight is progressing according to plan. Included in the ramp fuel would be the fuel calculated for the trip, an extra ammount of fuel called contingency for any unexpected deviations from the planned course of events, fuel to get to a diversion and fuel to hold for a while. Some flight planning for example that for an ETOPS flight would call for a more stingent fuel planning taking into account cabin decompressions, engine failures etc whilst a fair distance from a sutible airfield.

There will probably be better answers but I hope this helps a bit.

[windypops]

"I know that the FMS aboard large transport aircraft calculates fuel burn "

It's not just large transport aircraft that have FMS, our King Airs do too :ok:

As with all computers it's a case of "garbage in = garbage out" so there is still the human element as it's us who input the figures.

We do manual load sheets to ensure we are not "outside the envelope dude", and will plot Take Off, Landing and Zero Fuel Mass on these.

We will then fire up the FMS and input the data and then using the weights it has calculated we refer to our tables to get V1, Vr, V2. We also get a landing Vref at this point in case we have to come straight back at that mass. Technically of course we wouldn't come back at THAT exact mass as we would have burnt a few pounds during take off and the subsequent few minutes to get back onto final, but you get the point of the exercise.

Prior to landing we use the FMS to get our expected landing weight to again get our Vref speeds. If we subsequently get a delay obviously we revisit those figures.

[SNS3Guppy]

We don't do a weight and balance calculation during flight. That's part of preflight planning. We calculate the takeoff center of gravity, and ensure that the center of gravity remains within limits throughout the flight, taking into account fuel burn.

We have computers on board and use a computerized weight and balance program. Our operation carries loadmastes on board who do this, but all pilots are required to know and demonstrate the system, as well as use the program to perform the calculations and print the results, in the field and during training.

The complete weight and balance is necessary for us to do our takeoff performance calculation.

During flight, we keep track of fuel burn closely. We monitor it from each tank and engine, as well as overall fuel burn and balance. We keep a clipboard with the flight plan, and check off our time over each waypoint, comparing it to the forecast time, as well as forecast fuel burn and fuel remaining. This enables a continuous, accurate ongoing calculation of fuel burn and remaining. This enables us to know how we're doing at any given point on the flight plan, compared to how the fuel and time was originally calculated, and to adjust or divert, accordingly.

In our case, the gross weight goes in the FMS before departure, to use in the Performance Management System, but we still perform our own calculations at each point in the flight; regularly during cruise, any time an altitude change is made, with weight changes during fuel burn, and of course, takeoff and landing. We do these calculations not from the information the FMS provides, but from our own ongoing calculations.

A record of the entire process, including our calculations, is kept by the company for a set interval, after the flight.

[AnthonyGA]

Thanks for all the answers. It makes me think of something else: Do the computers/people who assign seats for passengers take weight and balance into account? Logically you'd load passengers seat by seat and row by row, but this obviously wouldn't be optimal for weight and balance, so is there is a system that makes sure that passengers are evenly distributed around the aircraft? What about divisions between areas for different classes (economy, business, first, etc.)? If first class is all up front and nobody is riding in first class, is that a problem, and if it's a problem, how is it handled?

[Out Of Trim]

Do the computers/people who assign seats for passengers take weight and balance into account? Logically you'd load passengers seat by seat and row by row, but this obviously wouldn't be optimal for weight and balance, so is there is a system that makes sure that passengers are evenly distributed around the aircraft? What about divisions between areas for different classes (economy, business, first, etc.)?


Usually, a Load Controller has looked at a certain flights expected passenger booked load and an expected cargo load before the passengers are checked-in. Most departure control systems can be set to offer the check-in staff seating prompts to keep the aircraft evenly balanced or certain seat rows may be blocked in the system to enforce this.

During this process then baggage and cargo can be placed in the most appropriate hold positions to get as close as possible to the "optimum trim" for departure. The loading of bags can often be finely adjusted during the last 30 - 40 mins to departure after check-in desks are closed to achieve this.