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Introduction to fuel planning for dispatcher by SoftAir SCRL - 18 October 2005 1

By Capt. (Rt) Jean De Rycker

Introduction to

FUEL PLANNING

for Dispatcher

download from www.softair.be/Download/IntroDis atchers. df


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Rules and Regulations.

2 International systems, slightly different (Pax weight and Route Reserve):

JAR = Joint Aviation Rules (Europe)

FAR = Federal Aviation Regulations (USA)

Minimum Required Fuel Regulations:

JAR (All) Fuel Required = (Trip Fuel + 5%) + [Alternate + Holding (30/1500 Ft)] Fuel

FAR (Intl) Fuel Required = Trip Fuel + 10%FtTime + [(Alternate + Holding (30/1500 Ft)] Fuel

FAR (Dom) Fuel Required = Trip Fuel + 45 (in Cruise) + Alternate Fuel


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B) DefinitionsDOW

Dry Operating Weight: Weight of the empty aircraft, without payload and fuel but in flying conditions(with oil, water and crew), Fixed for a given configuration but can vary depending on the length ofthe flight and the destination (Cabin Crew, Catering). It is also called OEW, Operating Empty Weight.

ZFWZero Fuel Weight: Weight of an aircraft with a payload (otherwise it is the DOW!) but still without Fuel.It varies only with the payload.

LDWLanding Weight: Weight of an aircraft at landing. Varies with the ZFW (and thus its payload) and thefuel reserve (on board for landing at destination).

TOWTake-Off Weight: Weight of an aircraft at take-off. It varies with the payload and the total fuel onboard.

In summary: DOW = Fixed by the aircraft configuration

ZFW = DOW + TRAFFIC LOAD

LDW = ZFW + RESERVE FUEL (*)

TOW = LDW + TRIP FUELOr,

TOW = {[(DOW + TRAFFIC LOAD) + RESERVE FUEL] + TRIP FUEL}ZFW .................................................

LDW................................................TOW

Except for the DOW, all have maximums. An M will then precede the abbreviation.

MZFW: Structural limitation. Can never be exceeded.

Maximum Traffic load = MZFW - DOW, except if belly limited [Bly] (**)

MLDW: Structural limitation, or due to landing Performances. (Mainly for High airport elevation)

MTOW: Structural limitation, or due to take-off Performances (Airport elevation, Runway length,OATC and Wind component).

(*) RESERVE FUEL: Minimum fuel to fly from Destination to Alternate plus a quantity to Hold 30 at1.500 Ft AGL + Route Reserve (Contingency) of 5 % of Trip Fuel if JAR, or10 % of Trip flightTime ifFAR-International, or a total of45 and no holding ifFAR-Domestic.

(**) [Bly] = Max. belly capacityOn some old passenger planes (B-707, DC8) we can be limited by the maximum Belly Capacity:

Maximum Load = (Seating Capacity x Pax Weight) + Belly capacity

This one can be inferior to (MZFW DOW).

Ex: B707-300 Pax: DOW = 68.0 To ; MZFW = 104.3 To ; Max Load = MZFW DOW = 36.3 To190 Seats (x 90 Kgs = 17.1 To) + Max Belly (12.0 To) = 29.1 To < 36.3 To


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C) Aircraft Loading and Fueling

While its fuel tanks are empty an aircraft can accept a maximum load limited structurally by itsauthorized weight without fuel (its Maximum Zero Fuel Weight). If you fill up the fuel tanks gradually,you will be able to fly over an increasing distance, until you reach the maximum weight for take-off.This maximum Load /Fuel combination corresponds to a maximum distance.

These flights have been Zero Fuel Weight lim ited.

Beyond this distance, the maximum load will have to decrease for 2 successive reasons:

1. The first one is that passed this distance, to fly further away, you would need to take more fuel.But as the aircraft's weight at take-off is at its maximum, you are obliged to decrease thepayload to take fuel instead. In fact, one gets heavier in fuel to the detriment of the payload, tokeep the same Take-off weight.These flights are TOW limited.

2. The second one is that if you still wish to fly further away, at a given moment, the fuel tankswill be full and the only way to fly farther will be to continue to decrease the payload toconsume less! Indeed, the less heavy you are the less you consume!

These flights are now Fuel Capacity lim ited.

Consequently, the maximum distance to cross - Maximum Range, will be empty (Ferry), which seems

to be logic. See, here below, the simplified graph.

Traffic Load (Ton) = Fct [Distance (AirNm)]

The distances we are referring to, are Air Distances to which corresponds a flight time that in thecase of the Maximum Range will be the Maximum Endurance. For each Air Distance, correspond aGround distance and a Wind Component (W/C) expressed in Kts.


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Sample for the A310-300

And/or to compare different planes


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D) Detailed Fuel Planning

A flight is determined by what one calls a Leg that includes the phases of:

Taxi. (To which APU must be included) Take-off

Climb Cruise Descent Approach and landing maneuvers

Moreover at landing at Destination, the aircraft must always dispose of a fuel reserve that will allowher to reach the Alternate airport and to hold over there 30' at 1500 Ft above ground level (page 3).

Then, as seen (pages 2 & 3) we have the Route Reserve, also called Cont ingency, who is in fact thefuel quantity that the company/government requires on top of the Trip Fuel necessary for the flight.

The JAR use 5% of the Trip Fuel but is variable, with a minimum of 3% under special conditions.The FAR (Intl) foresees a minimum of10% of the (Tr ip) Fl igh t T ime(at Long Range Cruise), but canbe increased by the company.The FAR (Domestic) required only 45 in cruise.

There are three types of transport:

Pax: carrying exclusively passengers Cargo: carrying exclusively freight Combi: a combination of the above two (No longer allowed in certain countries, but still in

use by some Air Forces and few airlines.)

The Pax Weight: For the passengers aircrafts, each passenger (with its luggage) will generally

weight between 85 and 100 kg. following the JAR/FAR orCompany rules.The European norms (JAR) and the US norms (FAR) are a bit different. (It used to be 90 kgs perpassenger following IATAs norms)

JAR

[Kg] Scheduled Charter

Domestic Route 95 87

Continental Route 97 89

Intercontinental Route 100 92

FAR (From Lbs)

[Kg] Summer Winter

Domestic Route 92.9 95.2International Route 95.2 97.5


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To calculate a flight we need several elements:

The Aircraft parameters and limits as: the DOW, MZFW, MLDW and the MTOW. (Page 3)(The difference between the MZFW and the DOW gives the maximum allowed Traffic Load.)

The Reserve Fuelrequired. (Page 2, 3 & 6)

And additionally:

The Maximum Fuel Capaci ty:the capacity of the tanks.

The Taxi/APU fuel(At departure) and the Holdin g Fuel(30/1500 Ft) can often be consideredto be constants following the company policy.

The Departure Airport - with the MTOW - Performances, as required,

We have a data linking at the same time the aircraft and the take-off airport: the Limit TOW.Lets remind us that an aircraft is mainly structural lylimited at take-off. However, for a givenRunway and for no wind (Normally, the Wind component on takeoff is a head wind and then, it can

only help), it is a possibility to be more limited by the performanceson Take Off if:

1. - High Airport Elevation and/orHigh OATC

2. - Short Runway Length.

You will have to use the Weight Book of the Plane.For a given Plane, and for a given Airpor t s Runway, we have a list ofPerfo TOWin function ofthe wind component W/C and the temperature OATC. Select the corresponding one.

The Destination Airport. Here, we have to check that we are not above the MLDW.(It is rarely the case in normal conditions).

The Alternate Airport, for the selection of an Alternate airport, a distance < 100 Nm betweenDestination and Alternate is judged marginal.

We can also notice that in specific cases, the Alternate Fuel can be replaced by a Two hours flyingin cruise. This is the case of the so-called "Isolated" airports, when no Alternate Airport is available.

We also need:

The En Route Wind Component W/C Kts

If we consider the "Ground Distance between the two airports we will add a wind component W/C toobtain the corresponding "Air Distance" and Times:

1. - The Flight Time in Hours and Minutes.

2. - The Block Time which is the Flight Time plus the taxi.

The Taxi is usually estimated to be 20 minutes.The Block Time is then equal to [Flight Time + 20] rounded to the 5 minutes.


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Fuel policies

Most of the time, a flight is made in the Normal Minimum Fuel consumption configuration.Still, there are 3 other ways for calculating the Fuel requested:

1) Maximum Economic Fuel.

On top of the normal Traffic Load, we will load the plane with the maximum fuel possible. In the caseof the fuel price at destination is too expensive, we then will be limited mainly in LDW, sometimes inTOW or in fuel capacity F/C.

Remarksa) Fuel Transpo rtat ionOne has to take into account that to transport additional Fuel, the Extra Fuel at destination is not thesame as the Extra Fuel added at the departure. We can say that part of this fuel is use for its owntransport!NB: In a very conservative manner, let us keep in mind: 50 Kgs/Tons/Hrfor all big jets.

b) Cost of transportCarrying Fuel can be interesting when there is sufficient difference in price between the 2 airports.However, as the Extra Fuel increases the consumption, the break-even has to be carefullydetermined. IfK is the Transport Coefficient, we have:

The difference of 1 Tons at LDW means a difference of (K x 1) Tons at TOW.Example: With K = 1.3, if an additional 1 Ton is desired at arrival, 1.3 Ton has to be added atdeparture. It costs 300 kgs of extra fuel to carry 1 additional Ton.

Costs

Extra Cost at departure XF Dep x Pd (Pd = Price at Departure)Economies at Arrival XF Arr x Pa (Pa = Price at Arrival)

Then, if the flight time is the same, it is interesting to take Extra Fuel if:

(XF Arr x Pa) (XF Dep x Pd) >= 0

And as XF Arr = XF Dep / K

We have: Pa / Pd >= K

Or also if:

c) Cost Index

Ci Min: ifsmall Time Cost and large Fuel Cost, then go forMinimum Fuel - Max Range (MRC)

Ci Max: iflarge Time Cost and small Fuel Cost, then go forMinimum Time - Max Speed (MMO)

Basically, if the chosen Mach number is close to LRC (So, a small Ci), it will give the operator the bestpossibility to bring the greatest load on the longest distance, regardless of the cost. Obviously, the lessyou burn the more loads you can take or, the more far you can go...

In practice, it is sometimes more economical to fly faster. (Refer to your Company policy)


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2) Required Landing Fuel. (Additional fuel needed))In this case, we impose a mandatory fuel quantity at landing by giving priority to the fuel, that is to saythat if the flight is limited (in Landing or in Take-off, but of course not in Fuel Capacity), we will have todecrease the Payload to satisfy the Required Landing Fuel, following the tanks capacity.

The additional fuel can then be considered as Traffic Load.This mode of computation can be interesting in the case there is no fuel available at destination and

that we know the required fuel quantity to make a flight to an airport where refueling is possible.

3) Round Trip fuel.This mode of calculation (the last one) allows you to calculate a Round Trip flight without taking anyfuel at Destination. This can be the case for instance if we send an aircraft to a place where it cannotrefuel. It is of course cheaper to fly back without a Fuel StopIn this case, the return load will have the priority.To use this mode of Fuel Policy, we first solve the return flight in Norma l m in imum Fue lmode andwith its requested Payload. By this way we know the corresponding fuel quantity required to do thisleg. We then create the outbound flight for which the policy becomes the requ i red land ing Fuelwith aquantity of fuel corresponding to the consumption of the return flight. The wind should be reversed.

Fuel Stop

Sometime it is necessary to make a Fuel Stop. The difficulty is to find an acceptable airport for thisFuel Stop. Indeed this one has to be on the initial flight route or at least with the minimum deviation.The Fuel Stop is calculated as being an additional Legin the flight and generally will be found bymaking the research in the neighborhood of 50% of the trip.

It can be summarized in searching in the red zone, here in the below earth scheme in which the FuelStop airport C should be.

A

B

C


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In Flight Reclearance/Redispatch

This procedure permits aircraft to carry less Route Reserve (contingency) fuel and is interesting incase of fuel capacity or takeoff limitation. Then, if the Traffic Load is limited in T/O or in F/C and if noExtra Fuel is embarked, it is possible to increase the first one by a value inferior or equal to the RouteReserve (that will be reduced by the same quantity). To do so, we need to have an en-route airport to

land if the fuel on board at a predetermined Decision Po int (DP)/Point o f Redisp atch (POR)islower than the minimum fuel required t o con ti nueto the final Destination airport:

JAR Fuel required to cont inue= (Trip fuel to go + 5%) + (Alt. + Hold.) Fuel

FAR (Intl) Fuel required to cont inue= (Trip fuel to go + 10% FT) + (Alt. + Hold.) Fuel[Not applicable to FAR (Dom), because the contingency fuel (45) does not depend of the flight time.]

The payload is increased while the Ramp fuel is diminished by the same value and the consumptionstays identical, as the total weights have not changed. This of course is only valid for small payloadads, less or equal (* Rmk) than the Route Reserve.Normally, a Reclearance/Redispatch is suitable to increase the traffic load, not to decrease therequired fuel; however such a decision is left to the crew, the dispatchers and the company.

* Rmk: The maximum Fuel reduction is 5% of the trip fuel (JAR) or 10% of the trip time (FAR) from

the Departure Airport to the DP/POR. The Route Reserve to go should be embarked in place ofthe initial route reserve, from the departure airportHowever, the main thing is the Fuel on board at the DP/POR


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E) Some samples (3)

1. - Simple Fuel Planning Sample: md-11/JAR at M .84

md-11 at Mach .84: DOW = 132.5 tons.

Traffic Load = 37.5 tonsFlight 4.500 Nm, W/C -25, Alternate distance 160 Nm, W/C = 0

The Fuel Planning problem is solved in reverse order, starting with a landing at the Alternate andending with a takeoff at Departure.

Aircraft LDW at Alternate in normal condition is equal to the ZFW.Rmk: We consider no additional fuel such as, company special reserve or extra fuelIf some additional fuel exists, it should be considered as Traffic Load.

DOW (or OEW) + Traffic Load = Alternate LDW = ZFW (Should be


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Sequence

(End) 5 4 3 2 1 (Start)

RW TOW LDW ZFW


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2. - Graphical way of calculating the Trip Fuel


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3. - Another personal - graphical way of calculating the Trip Fuel: A300-B4

a) First, we calculate the Destination LDW:. - From the Pax number we go to the 90 Kgs (Pax) line to find the Pax weight (222 x 90 = 20.0 tons)

. - Then we go to the Extra fuel if applicable (+ 5 Tons)

This means that 20.0 + 5.0 = 25.0 is considered as total Traffic Load.

. - From there we go up to the DOW (91Tons) line,

. - We follow the oblique line (Alternate LDW = 116 Tons) until the intersection with the reserve fuelor [6.5 tons (Alt at 400 Nm in 70 or 01H10) + 2.5 tons Holding] line, witch give:

Dest inat ion LDW= 116.0 + 9.0 = 125.0 Tons

b) Then, we check the W/C (-40 kts) on the Ground Distance (1.280 Nm), witch gives the Air Distanceand the Fl ight Time(03H10). We then add the Route Reserve (Contingency) of 5% and goes up untilthe destination LDW (125.0).

c) At once, we found:The Trip Fuel(20.5 Tons) and the TOW (145.0). Not very precise ( 0.5 To), but easyand fast.(We also found the Climb time to FL 330: 23)


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Introduction to fuel planning for dispatcher by SoftAir SCRL 18 October 2005 17

END

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