Fuel

A detailed fuel planning manual, which will contain much more pieces of information will be published soon. I just tried giving you a „starter-kit“ of significant calculations. This article is to be considered a bridgeover

Apparently, you have accomplished to build a flight plan you want to fly. That is a key-fact in planning your amount of fuel. According to our flight plan, we have to bridge 295 nautical miles from Vienna to Berlin.

The easiest way to figure out the total distance will be to add up all the numbers enroute your way, which are given in oblongs below the actual path. Especially SID- and STAR chart do not have distances. Thus, you have either to work with navigational instruments and nm-scales or make a good guess of 10-15 nm each.

Now, we figured out how far our planned route will be, but not how long it will take us.

ATTENTION: The amount of fuel we will need is in no way directly linked to the distance of our trip. For clarification: think on different types of weather! Thus, in order to go the easiest way to understand fuel planning we will exclude winds aloft.

First, you need to know four basic numbers:

  • KIAS → Knots Indicated Airspeed – this is the airspeed shown on the airspeed indicator. (A synonym of indication is foretelling another will be a hint!) To identify see Aircraft Manual (Operation Manual Bravo) for Speed at Cruising Altitude.
  • KTAS → Knots True Airspeed – we will move through air at this true speed.
  • Groundspeed → this is KTAS + Speed of Wind (may also be negative!)
  • „Fudge Factor“ → KIAS + x, considering a given height, will be KTAS. The easiest way without a flight calculator will be to multiply KIAS with 2%. (If fuel calculation time exceeds flight time, the hobby starts to get boring. Hence, we don't want to be more Catholic than the Pope.)

I assume an example might help most. We will fly our route (only today) with a Boeing 767-300ER. This Aircraft will fly most likely 290 KIAS at FL340 (westbound). I've chosen this aircraft to show some comparison when we deal with international flights.

Step 1 Step 2 Step 3 Result
290 KIAS times 2% equals 5.8 5.8 times (altitude-100=34) equals 197.2 Add this result (197.2) to the KIAS (290) to get KTAS 487.2 KTAS

Hence, we can calculate very easy how fast we will travel within one minute (KTAS / 60 minutes = 8.12 nm/min) and, furthermore, we can also calculate how long we will be in the air (trip/8.12= 36.34 minutes).

Apparently, ascent and descent will be flown with less speed. Thus, let us consider an extra amount of time of about 12 minutes. (Remark: We only stretch the time for ascent and descent and do not set 12 minutes total for both!)

The final trip time will be close to 48.34 minutes.

Nevertheless, what happened, when the designated airport is closed? We will need to divert to another airport. Let us take EDDP (Halle/Leipzig) as our first alternate.

The distance from Berlin Tegel to Halle/Leipzig will be 78.4 nautical miles. 78.4 nm / 8.12 nm/min = 9.66min. The time we will need to continue from Berlin to Leipzig will last 9.66 minutes.

The final trip time (including our alternate time) will be close to 60 minutes.

The typical fuel burn per hour of a Boeing767-300ER at cruising altitude will be around 6000 pounds per hour and engine. Let us take this number as another key-figure. The amount of fuel you will burn during ascent can be offset with the descent.

1 hour times (2x6000lbs) equals 12'000lbs/hour (B767 - twin engine jet!) including alternate fuel
  • Reserve fuel: I suggest 45 minutes for reserve. Thus we add 0.75 times (2x6000lbs) = 9000lbs.
  • Holding fuel: When Berlin Tegel is closed and Halle/Leipzig goes under heavy traffic, we might need to enter the holding pattern at Halle/Leipzig for a maximum of 30 minutes. Hence, we add another 0.5 times (2x6000lbs) = 6000 lbs
  • Ground operations (Taxi fuel): (30 minutes) will be added with half the pounds per hour we actually use during cruise flight. Thus 12'000/2/2 = 3000lbs.
We will need a fuel quantity of all added up figures and will conclude in about 30'000lbs of finest A1 jet fuel for performing a safe flight from Vienna to Berlin.

There are two points we did not mention in the above text. These will be called:

  • Unuseable Fuel,
  • Captains Discretion Fuel.

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