Fuel Policy and Fuel Monitoring — Page 32, Lesson 41

I want to walk you through the fuel policy and fuel monitoring section. We're going to look at two specific situations where additional fuel might be required, and then I'll explain how contingency fuel is calculated. First, let's talk about holding fuel. There are two cases where you need to plan for holding time. The first one is when you're operating a flight with a destination alternate aerodrome — that's a backup airport you can divert to if needed. In that case, you plan for holding for 30 minutes at 1500 feet above the destination aerodrome in ISA conditions. ISA stands for International Standard Atmosphere — it's the standard temperature and pressure reference model we use in aviation. The second case is when a flight is operated without a destination alternate aerodrome. In that situation, you plan for holding for 15 minutes at 1500 feet above the destination aerodrome, again in ISA conditions. On most flights, Additional Fuel is not required, but in either of these two cases, it may be necessary. Now let's move to the calculation of contingency fuel. The numerical calculation of taxi fuel, trip fuel, alternate fuel, and final reserve fuel is fairly straightforward. Taxi fuel is usually a standard allowance — a fixed amount you expect to burn moving on the ground. Trip fuel and alternate fuel are extracted from graphs or tables from the appropriate Operational Flight Manual — that's the manufacturer's approved document for that specific aircraft type. We'll practise that process in later chapters. Final reserve fuel is a simple calculation. For a jet or turboprop aircraft, it's based on 30 minutes of holding at endurance speed. For a piston-engine aircraft, it's 45 minutes of holding at endurance speed. Endurance speed is the speed that gives you the longest possible flight time for the fuel you have. However, contingency fuel can vary depending on the type of operation. Contingency Fuel is defined as the higher of two values, which I'll label A and B. Value A is as agreed with the appropriate national aviation authority. It is 5% of the planned trip fuel. If you do in-flight replanning — meaning you change your plan while airborne — then it's 5% of the trip fuel for the remainder of the flight. No en route alternative is needed in this case. Additionally, if the operator has a fuel monitoring programme and agrees a particular method of statistical analysis which includes standard deviations — the details of that statistical method are beyond what we need for the ATPL — this 5% figure can be reduced yet further by agreement with the authority. Value B is an amount to fly for 5 minutes at holding speed at 1500 feet — that's 450 metres — above the destination aerodrome in standard conditions. Contingency Fuel is the higher of A and B. For the most part, contingency fuel will be based on 5% of trip fuel — that's value A. But be aware of the alternative, value B, because exam questions do occur where holding for 5 minutes at 1500 feet will be a higher figure than 5% of trip fuel. So you always take whichever is greater.