The Earth
The Solar System & Time
Using Aeronautical Charts
Basics of Navigation
Distance, Speed & Time
Vertical Navigation
Fuel Planning
Practical Navigation Techniques
Radio Navigation
Practice Exam

Fuel Consumption

Fuel Units

In aviation, fuel quantity and fuel consumption can be expressed in:

Litres and litres per hour (L/hr)
US gallons and US gallons per hour (USG/hr)
Imperial gallons and imperial gallons per hour (Imp. Gal/hr or IG/hr)
Kilograms and kilograms per hour (kg/hr)
Pounds and pounds per hour (lb/hr)

Conversions between volume (litres, USG, or Imp. gallons) and weight (kg or lbs) is a necessary skill as you will find, for example, American aircraft flight manuals using US gallons but the European refuelling equipment using litres. This is covered in the next lesson.

Specific Gravity

Specific gravity is a term used to describe how much a certain liquid weighs. The standard aviation fuel for piston engines is known as AVGAS. The specific gravity of AVGAS changes slightly with temperature but we typically assume AVGAS has a specific gravity of 0.72.

This means that 1 litre of AVGAS weighs 0.72kg or 720 grams.

So to calculate the weight of your AVGAS, you can multiple the quantity in litres by 0.72. For example, if you have 75 litres of AVGAS on board, the weight is:

Fuel Requirements

Fuel requirements for PPL flying are found in the regulations under Part-NCO (non-commercial operations). Specifically, NCO.OP.125 says that for non-commercial operations we are required to carry sufficient fuel to fly to the aerodrome of intended landing plus fuel to fly at normal cruising altitude for an additional 30 minutes during the day or an additional 45 minutes at night.

Fuel to fly to the aerodrome of intended landing” includes all the fuel required for engine start, taxi, takeoff, climb, cruise, descent, approach, and landing.

However, the above is an absolute minimum requirement and many flight schools will follow the good practice of requiring:

Engine Start & Taxi Fuel
The fuel you expect to burn before take-off
Trip Fuel
The total fuel required from take-off at the departure airport to landing at the destination airport. This includes the cruise fuel and any additional fuel burnt during takeoff, climb, approach, and landing.
Contingency Fuel
This is 5% of the planned trip fuel which is added for any unforeseen increases in flight time
Alternate Fuel
Fuel required to fly from the destination airport to a suitable alternate airport
Final Reserve Fuel
Fuel to fly at normal cruising altitude for an additional 30 minutes during the day or an additional 45 minutes at night

Each flight school’s policy varies so make sure to check with your instructor!