Mercedes Mullins
Fuel weight is a critical factor in aviation safety, and the amount of fuel drained from an airplane depends on various factors, including the aircraft's weight and balance criteria. If an aircraft exceeds the maximum allowable weight, it may suffer structural damage or even break apart upon landing. Therefore, it is crucial to ensure that the aircraft's weight, including fuel weight, adheres to the specified limits. Fuel can be drained from the sumps located beneath the wings or siphoned directly from the tanks using a hose or aquarium tubing. However, caution must be exercised due to the safety risks involved in fuel handling. In some cases, burning off excess fuel by taking a short flight before the planned trip or circling near the departure airport can be an alternative solution to draining.
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What You'll Learn
Draining fuel from sumps beneath the wings
Draining fuel from an aircraft is a crucial maintenance task that helps ensure the longevity and efficiency of the aircraft. Over time, dirt, debris, and moisture can accumulate in the fuel tank, leading to contaminated fuel. This contamination can cause clogged fuel filters, reduced engine performance, and even long-term damage to the engine.
To drain fuel from the sumps located beneath the wings, you will need a tool with a rod to open the valve on the sump. Place a container beneath the sump to collect the drained fuel. A tube with a funnel attached can be used to direct the fuel into the container. It is important to note that you should not use the cockpit fuel gauges in a light GA aircraft to determine the amount of fuel in the tanks, as these are only required to be accurate when reading as empty. Instead, refer to the pre-marked indicators inside the tanks or use manufacturer-approved gauges to determine the fuel quantity.
Before draining, it is essential to draw a sample of fuel from each sump and screen drain it into a transparent container. Check for any signs of contamination, such as water, dirt, rust, or other impurities. If the fuel is contaminated, do not pour it back into the tank. Dispose of it according to EPA regulations and airport procedures. Many airports provide fuel disposal containers or sump barrels for this purpose. If no other option is available, avoid dumping the fuel on the ground. Spread it over a large area to allow for quicker evaporation.
If the fuel is uncontaminated, it can be filtered and returned to the tank for reuse. However, ensure that you have the proper equipment, such as a fuel tester or a GATS jar with a built-in filter, to safely transfer the fuel back into the tank.
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Siphoning fuel out of tanks
The amount of fuel that needs to be drained from an airplane depends on the weight and balance criteria of the aircraft. Before draining any fuel, it is important to verify that removing the fuel will keep the aircraft within weight and balance limits and that there is still enough fuel to safely complete the flight.
There are several ways to remove fuel from an aircraft, including siphoning it out of the tanks. To siphon fuel out of an aircraft's tanks, one can use the fuel sumps located beneath the wings of many piston aircraft, or use a siphon hose or clear aquarium tubing through the gravity filler ports on the top of the wings. The filler ports are often on the highest part of the tanks and may require a long hose to siphon the gas. A siphon pump can also be used, but not all FBOs have this capability.
It is important to note that there is no quick and efficient way to safely unload fuel from an aircraft. In some cases, it may be faster to burn off the excess fuel by taking off and flying around the airport for a few hours.
Additionally, it is crucial to accurately gauge the amount of fuel in the tanks before beginning the process of removing fuel. Some tanks have pre-marked indicators inside the tanks where the fuel level corresponds to certain markings or metal tabs. There are also gauges available for purchase to determine the quantity of fuel in the tanks, but it is important to use one that is approved by the manufacturer for the specific make and model of the airplane.
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Burning off excess fuel
Determining Excess Fuel
Before initiating any fuel-burning procedures, it is crucial to accurately gauge the amount of fuel in the aircraft's tanks. Some aircraft have pre-marked indicators inside the tanks, while others use measuring sticks or gauges specifically approved by the manufacturer. It is important to note that cockpit fuel gauges in light aircraft are typically unreliable and should not be solely relied upon.
Burning Fuel During Flight
One method to burn off excess fuel is to perform a flight prior to the arrival of passengers or cargo. By utilising takeoff, climb, cruise, and power settings charts from the Pilot's Operating Handbook, pilots can estimate the time and power settings required to consume the desired amount of fuel. This method ensures that the aircraft starts its primary flight with the optimal fuel load, improving overall efficiency and performance.
Burning Fuel in the Pattern
Another way to burn off excess fuel is by performing laps or practice landings at the airport before departing on the main flight. This method is particularly useful for burning off smaller amounts of excess fuel and can help pilots familiarise themselves with the airport and improve their landing skills.
Fuel Dumping
Fuel dumping is a technique used by some larger aircraft to release excess fuel, usually at high altitudes, to reduce weight during non-routine flights. This procedure is often coordinated with air traffic control to ensure the safety of other aircraft in the vicinity. In some cases, the dumped fuel is intentionally ignited using the aircraft's afterburner, creating a spectacular display of flames known as a "dump-and-burn." However, fuel dumping is generally not necessary for small GA planes, as they typically do not carry enough fuel to require this procedure.
Considerations
When dealing with excess fuel, it is important to consider the trade-off between fuel efficiency and having sufficient fuel reserves. Every pound of extra fuel impacts the aircraft's performance, including climb capabilities. Additionally, burning off fuel can incur costs, and pilots must ensure that they have enough fuel to safely complete their intended flight, including any reserves required by regulations.
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Fuel dumping in emergencies
Fuel dumping is an emergency procedure where an aircraft reduces its weight by releasing fuel before landing. It is a relatively uncommon practice that is generally used when a plane needs to land before burning enough fuel to do so safely. This may be necessary to prevent structural damage during landing, as planes are constructed to land at a certain weight.
During the early era of jet aircraft in the US in the 1950s and 1960s, the Federal Aviation Administration (FAA) mandated that aircraft with a ratio between maximum structural takeoff weight and maximum structural landing weight of greater than 1.05 must have a fuel-dump system installed. This rule was later changed, and Federal Aviation Regulations 25.1001 was enacted, stating that a jettison system was unnecessary if the climb requirements of FAR 25.119 (Landing Climb) and FAR 25.121 (Approach Climb) could be met, assuming a 15-minute flight.
Fuel dumping is typically performed at higher altitudes to allow the fuel to evaporate before reaching the ground. Pilots aim for an altitude of over 5,000 feet and dump fuel over remote areas to minimise the impact on people and infrastructure. However, in some emergency situations, aircraft may need to dump fuel over populated areas, which can cause health issues for those on the ground, such as skin and eye irritation, nausea, and breathing problems.
Not all aircraft are equipped with fuel dump systems. In such cases, pilots of smaller twin-jet aircraft have two options: burning off the excess fuel or performing an overweight landing. Burning off fuel can be achieved by making a flight prior to the arrival of passengers or utilising the different power settings during the flight as outlined in the Pilot's Operating Handbook.
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Weight and balance calculations
Calculating weight and balance is essential for flight safety. Different points on the plane hold various items, such as baggage, fuel, passengers, etc. If the weight is not equally distributed, it could result in compromised safety.
To calculate the weight and balance of an aircraft, you need to know the weight of each item on board and its position. The weight of the aircraft is calculated by adding up the weights of all the items on board. The balance is calculated by considering the moment, which is the force that an item places on the airplane. The moment is calculated by multiplying the weight of an item by the distance from a reference point, known as the "datum". The center of gravity (CG) is the position at which the airplane would balance if it were possible to suspend it at that point.
The weight and balance calculations can be done using graphs or tables provided in the Pilot’s Operating Handbook (POH) or Aircraft Flight Manual (AFM). The graphs or tables will show the moments produced by each item at different stations (e.g. front seats, rear seats, fuel tanks, baggage area, etc.) and the acceptable CG limits. The total weight and total moment can be calculated by adding up the moments and weights of all the items on board.
To calculate the weight of fuel, you need to know the number of gallons and multiply it by the weight of the fuel per gallon. The weight of avgas is 6 pounds per gallon, while Jet-A fuel weighs a little over 7 pounds per gallon. The weight of oil can be calculated in a similar way, with a quart of oil weighing around two pounds.
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Frequently asked questions
The tanks are generally placarded with their usable capacities, or this will be listed in the Pilot's Operating Handbook for the aircraft in question.
You can drain the fuel from the sumps, generally located under the wings. A tool with a rod would be required to open the valve on the sumps, and you could use a tube with a funnel on it to collect the fuel into a container.
If the plane is within gross weight but outside of CG, you can move some payload to another fuselage station to move the CG within limits. Then, do another weight and balance calculation.
There are safety risks associated with draining fuel. You must be very careful about the static that will build up from the falling fuel. There have been incidents of total losses due to defueling incidents.
You could siphon the fuel out of the tanks with a hose or aquarium tubing. Another option is to burn off the excess fuel by taking a flight prior to the arrival of passengers.
