Understandably a crucial element in flying jet aircraft, fuel calculations are carried out during three broad phases of flight; Immediately after fuelling, at top of climb (and every hour/major waypoint thereafter) and then after engine shutdown. The last of these is a simple addition of each fuel gauge, then used as a comparison to the flight plan to check for correct burn. A note of the remaining fuel is entered into the tech log for the next flight and use in the after fuelling calculations.
After Fuelling
After the fueller has loaded the amount of fuel requested for the flight, they will present the flight crew with a receipt showing amount of fuel pumped in litres.
The aircraft tech log requires the fuel loaded to be recorded and then cross-checked with the remaining fuel from the last flight (+/- 300kgs) to ensure the gauges are reading correctly.
Arrival fuel was 1000kg and 3200kg was requested by the flight crew for the next sector, as shown in the tech log below.
By adding the fuel in both gauges you can see the fueller has provided just over the required target amount, which is perfectly acceptable and probably considered a normal occurrence due to the way the fuel gauges operate. The JETA1 fuel receipt presented to the flight crew showed an uplift of 2855 litres. This information can now be entered in the tech log.
All the information required to complete the tech log is now present. Firstly, a conversion from litres to kgs is required to calculate the fuel uplift. As per your ATPL ground school exams, approximate specific gravity of JETA1 is 0.8.
2855 litres x 0.8 = 2284kgs
Now to find the calculated arrival:
3280 – 2284 = 996
and enter the last numbers into the tech log:
The calculated arrival fuel is well within the +/- 300kgs of arrival fuel, a tolerance dictated by the manufacturer showing the aircraft systems and fuel burn are correctly functioning.
Top Of Climb/Regular Fuel Check
This is a simple addition of all the fuel in the gauges. Subtracted from this value is the trip fuel required for the flight to the destination, not including any diversion or reserve fuel. The calculated value is then compared to diversion plus reserve fuel to see if the flight is running as per plan. Shortcuts, head/tailwinds, achieving the flight plan cruising level and aircraft payload are all factors affecting this figure.
Fuel Load With 30 Minutes To Landing:
Remaining Trip Fuel Required To Destination = 600kgs
Reserve Fuel = 1200kgs
Diversion Fuel = 1000kgs
Total Fuel = 3280kgs. 3280 – 600 (Fuel Required to Dest.) = 2680kgs
2680 kgs – 1200 (Resv. Fuel) – 1000 (Div. Fuel) = 480kgs.
This shows the flight is operating with +480kgs on flight plan fuel.
Airline Simulator Check Fuel Questions
Mathematical questions are included in a number of airline simulator checks. These are designed to test your mental agility under pressure and also your ability to prioritise and manage workload. Below is a generic example of the type of question you may face.
You are operating a four-engine aircraft with four fuel tanks. Each fuel tank has 20t of fuel. If each engine uses 4t of fuel per hour, how long can you remain airborne assuming no reserves or diversion fuel?
20t x 4 tanks = 80t , 4 engines x 4tph = 16tph , 80t ÷ 16tph = 5 hours
Continuing the question, if the aircraft has a ground speed of 550kts, how far can it fly with its fuel load?
550kts x 5 hours = 2750nm