Each year a number of aircraft accidents are related to fuel starvation, exhaustion or contamination. There were numerous reasons for these avoidable accidents: ranging from inadequate fuel systems knowledge by the crew, preflight planning issues, takeoff and landing checks and failing to monitor fuel consumption during flight. Or even failing to refuel the correct quantity before the flight.

As preflight of an aircraft is important, preflighting the fuel system is equally so. Determining fuel available, usable quantities and the use of a fuel management log will be the subject here.

Preflight Fuel Management

Before starting any flight you will need to determine the amount of fuel currently in the tanks. Assuming you have calculated the amount required it is just a matter of refueling with the amount required and you're good to go. Almost. It would be wise to check the available fuel by at least two methods: in an empty tank a known quantity can be refueled or you will need to use a calibrated dipstick for this type of aircraft.

Fuel Tank Construction
Due to the construction of a fuel tank and the location where the fuel inlet port and drain port are located, a certain amount of the fuel is unusable and some part of that is even undrainable. Unusable fuel (which includes undrainable fuel) is the amount of fuel that cannot be used in level flight. This amount can vary from model to model and in the aircraft flight manual you will find the specifics for your aircraft.
The experimental aircraft builder/owner must determine himself what the exact amount of unusable fuel is for each tank in his aircraft and make a note of that in the flight manual. Usable fuel is the only amount which can safely be used in a flight.

Great care must be taken when converting between liters, US and Imperial gallons. Some fuel stations refuel in liters whereas the aircraft fuel gauges show in US gallons and sometimes (to confuse matters even more) on the aircraft wing, near the fuel cap, the amount of that tank is shown in Imperial gallons.

Fuel Gauges
Fuel tank content is displayed on fuel gauges and these should be reasonable correct. Compare the indications of the gauges when dipping the tanks so accuracy can be checked. Remember that during some maneuvers, slipping skidding and in turbulence, fuel tank indications can and will vary accordingly. If the aircraft is equipped with a fuel flow indicator it's indications should be checked against the level of fuel in the tank after the flight and the expected calculated fuel consumption.

Fuel Tank Dipping
In some countries it is common to dip the tanks to verify the amount of fuel. It is the most accurate way. But as each aircraft (and tank in that aircraft) is somewhat different it is important to use the correct dipstick for your aircraft.

Each dipstick is calibrated to the fuel tanks of that aircraft. It should have the aircraft registration number marked on it too.

When dipping fuel tanks you will need to follow some simple guidelines:

• The aircraft should parked on level ground, make sure the tanks are not cross feeding. This will happen when the fuel selector is set to BOTH. Fuel will flow from the tank with the greatest amount to the other tank. This could be a problem if you need both tanks to be full. Just set the fuel selector to either RIGHT or LEFT.
• The dipstick must be held perpendicular to the wing unless stated otherwise in the aircraft manual. Usually wing construction, spar location is the culprit here.
• Always dip the tanks after refueling. Even when refueling with a known quantity.
• Do the refueling yourself. You are the pilot in command and you are responsible, do not rely on someone else.

If there is no dipstick for your aircraft, you can start the flight with full tanks and keep a good fuel log during the flight. But as dipsticks can be bought for a reasonable price, buy one and get it calibrated to your aircraft.

As you normally refuel the aircraft after the end of the day to keep the change of moisture as low as possible, it would be wise to dip and drain the tanks in the morning. Fuel theft has occurred in the past and if the aircraft was parked on a uneven surface fuel could flow from the higher tank to the lower tank and siphon out through the vents. Which would leave you with one tank empty.

Pre-takeoff checks

Having an engine failure just after takeoff could be the worst possible time. A number of these situations were related due to fuel problems and the majority was selecting an almost empty tank (or even switching fuel off due to incorrectly marked fuel selectors), and in aircraft with more than one fuel tank to select. Contaminated fuel has also caused problems in the past.

A lot of these situations can be avoided by using the correct preflight and pre-takeoff checks.

The list below is not complete but these checks are commonly done when verifying fuel supply and switching tanks.

• Select the least-full tank before engine start, this will make sure that this tank can feed the engine. Also listen for the fuel pump when switched on, with the engine is running you will not hear the fuel pump. Check for a rise in and a stable fuel pressure. With a gravity fed fuel system there will always be some low fuel pressure due to the design.
• Change to the fullest tank before run-up. This will stabilize fuel flow from this tank. Visually check when moving the fuel selector. Selection of the wrong tank (especially when flying different aircraft with similar fuel systems) can be deadly. If you notice, after takeoff, that the wrong tank was selected, wait till you are at a safe height, then switch the fuel pump on and switch tanks. When switching the fuel pump off, keep you hand near the switch. The engine pump could have failed.
• Keep monitoring the fuel quantity gauges, fuel pressures and fuel flow for normal indications. Scan the fuel pressure during takeoff roll and keep the fuel pump on until a safe height is reached and the aircraft is cleaned up.

It is important to be totally familiar with the fuel system of the aircraft you fly. Know the number of fuel tanks and quantities, normal fuel flow, number of fuel pumps (the Rotax 914 uses two electrical in series configured pumps) and check the emergency procedures for fuel related engines failures.