How do dispatch calculate vital information about the flight?
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How do dispatch calculate vital information about the flight?
Hello all,
I'm not sure if it's dispatch or the crew who calculate this. I know it's all computerized but if you were to do it by hand, what are the formulas and calculations for:
I'm not sure if it's dispatch or the crew who calculate this. I know it's all computerized but if you were to do it by hand, what are the formulas and calculations for:
- Flight Time
- Fuel Required
- Optimum Cruise Level (if that's even possible)
- Takeoff Distance
- Landing Distance
- TOD
- Descent Rate
- Optimum TOD for straight in landing. (For Example: If you were at FL380, how would you know what time to start your descent at 1200fpm?)
Join Date: May 2000
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Go into the performance charts for the airplane. After going through about a dozen of them (and maybe a couple iterations of fuel load), you will eventually come up with the answers.
Join Date: Nov 2010
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Oliver,
Intruder's response is a bit harsh, but that's probably because he doesn't know that you're 13 years old and interested in learning about flying.
However what he says is basically what you need to do, after you understand a bit more.
You should make a trip to a local flight school and have a chat with an instructor about flying, and possibly pick up an introduction to flying book that he/she can suggest for you.
I'd suggest, based on this question, that you might start to study the PPL "ground school", but since you have lots of time, get one or some of the books for aviation theory and start there.
Now, the actual formulae?
Well you've asked a lot of questions here, actually.
So, in the next few years, in Maths and Physics, you'll learn that speed = distance / time, and distance = speed X time, and those two formulae will answer most of the questions you've posed, but you will have to use them more than once for some questions, and in conjunction with similar formulae for other questions.
It would be best for you to get an aviation theory book to start with.
Intruder's response is a bit harsh, but that's probably because he doesn't know that you're 13 years old and interested in learning about flying.
However what he says is basically what you need to do, after you understand a bit more.
You should make a trip to a local flight school and have a chat with an instructor about flying, and possibly pick up an introduction to flying book that he/she can suggest for you.
I'd suggest, based on this question, that you might start to study the PPL "ground school", but since you have lots of time, get one or some of the books for aviation theory and start there.
Now, the actual formulae?
Well you've asked a lot of questions here, actually.
So, in the next few years, in Maths and Physics, you'll learn that speed = distance / time, and distance = speed X time, and those two formulae will answer most of the questions you've posed, but you will have to use them more than once for some questions, and in conjunction with similar formulae for other questions.
It would be best for you to get an aviation theory book to start with.
Hi Oliver
Good questions - answering all of those in detail would take a long time, but here are some points you might find interesting. I'm sure others will come in with more (and correct me if I get anything wrong) :-)
Take-off weight
The total weight of the aircraft is, dry-weight(no fuel) + Pax + Baggage + fuel + other bits (e.g. food trolleys, etc). The more non-fuel weight, the more fuel you'll need - plus on long flights you have to factor in the weight "cost" of having more fuel i.e. if you want 1000kg of fuel in the tanks when you start your approach you need to factor in the extra fuel burnt to carry that 1000kg across the atlantic (whatever). The max take-off weight cannot be exceeded - in smaller aircraft/longer flights this can mean that you can't actually fill all the seats.
Centre of Gravity (CoG)
The total weight of the plane must fit within a CoG strict limit - basic physics here (levers/seasaws) - the further away a weight is from the CoG the more effect it will have. As a result fuel, bags and Pax (sometimes) have to be moved to make sure they fit within the CoG. If the plane goes out of CoG then it can become quickly uncontrolled and crash - witness the B747 Afghan take-off where the load moved on rotate and the plane crashed within seconds.
Calculation of both of these are flight critical and are normally performed by the flight crew. With both doing these independent of each other, ideally using different methods and both comparing the results to make sure they get it right.
Total fuel required
This is fuel to get to where you are going + fuel to divert to another airport if closed + loiter time at second airport + safety factor. Total fuel is always calculated by weight not volume - power available from fuel depends on the mass of fuel burnt, fuel density varies with temperature. So once you have the mass of fuel required you check the temp and then work out how many litres you need. Important that you do this in either KG or lbs and that you KNOW which one you are using - witness B757 years back where both crew went from a KG plane to lbs plane and BOTH calculated the right amount of fuel in KGs and then loaded that number in lbs - both engines flamed out in the cruise, pilot pulled off an amazing dead stick landing on a military field in the middle of Canada (IIRC).
Fuel required depends on flight plan - basically the higher you fly the better the fuel economy so complex set of equations based on flight time, altitude over time and starting weight of the aircraft, etc. Calculations also have to take account of possible engine failure, most planes cannot cruise as high with one engine out plus dead engine generates more drag so you have to work on that being the case - I think the rules for ETOPS cover diversion to alternate on engine failure as opposed to carrying fuel to make it all the way.
Flight time depends on wind at altitude - headwind = more time, tail wind = less time. Heathrow can get interesting in the morning if the jet stream was different from forecast i.e. lots of transatlantic flights arriving, all low on fuel due to increased headwinds and all wanting to land right away. Happens less as forecasting get better.
Hope these points help/are of interest.
Cheers
Mac
Take-off weight
The total weight of the aircraft is, dry-weight(no fuel) + Pax + Baggage + fuel + other bits (e.g. food trolleys, etc). The more non-fuel weight, the more fuel you'll need - plus on long flights you have to factor in the weight "cost" of having more fuel i.e. if you want 1000kg of fuel in the tanks when you start your approach you need to factor in the extra fuel burnt to carry that 1000kg across the atlantic (whatever). The max take-off weight cannot be exceeded - in smaller aircraft/longer flights this can mean that you can't actually fill all the seats.
Centre of Gravity (CoG)
The total weight of the plane must fit within a CoG strict limit - basic physics here (levers/seasaws) - the further away a weight is from the CoG the more effect it will have. As a result fuel, bags and Pax (sometimes) have to be moved to make sure they fit within the CoG. If the plane goes out of CoG then it can become quickly uncontrolled and crash - witness the B747 Afghan take-off where the load moved on rotate and the plane crashed within seconds.
Calculation of both of these are flight critical and are normally performed by the flight crew. With both doing these independent of each other, ideally using different methods and both comparing the results to make sure they get it right.
Total fuel required
This is fuel to get to where you are going + fuel to divert to another airport if closed + loiter time at second airport + safety factor. Total fuel is always calculated by weight not volume - power available from fuel depends on the mass of fuel burnt, fuel density varies with temperature. So once you have the mass of fuel required you check the temp and then work out how many litres you need. Important that you do this in either KG or lbs and that you KNOW which one you are using - witness B757 years back where both crew went from a KG plane to lbs plane and BOTH calculated the right amount of fuel in KGs and then loaded that number in lbs - both engines flamed out in the cruise, pilot pulled off an amazing dead stick landing on a military field in the middle of Canada (IIRC).
Fuel required depends on flight plan - basically the higher you fly the better the fuel economy so complex set of equations based on flight time, altitude over time and starting weight of the aircraft, etc. Calculations also have to take account of possible engine failure, most planes cannot cruise as high with one engine out plus dead engine generates more drag so you have to work on that being the case - I think the rules for ETOPS cover diversion to alternate on engine failure as opposed to carrying fuel to make it all the way.
Flight time depends on wind at altitude - headwind = more time, tail wind = less time. Heathrow can get interesting in the morning if the jet stream was different from forecast i.e. lots of transatlantic flights arriving, all low on fuel due to increased headwinds and all wanting to land right away. Happens less as forecasting get better.
Hope these points help/are of interest.
Cheers
Mac
