What Happens if an Airplane has No Fuel Pressure?

You are cruising at 6000 feet and check the gauges and see the fuel pressure is low. What happens if an airplane has no fuel pressure?

No fuel pressure means no fuel is being fed into the engine. If the issue is resolvable, such as a faulty pump, the pilot will use the auxiliaries to maintain flight. If the plane goes into fuel starvation, it could result in an engine failure, forced landing, or even a stall and crash.

Fuel systems on modern planes are very complex and often come with backups. If one component fails, there are usually substitutes that can be used to maintain flight and land safely.

According to webruss.net, a low fuel pressure indication can be quite stressful. It is important to pay attention to the other components of the plane and especially the engine.  If the engine is running fine, the chances are that the low fuel pressure is due to something not very serious. However, it is best to get it checked out by an aircraft mechanic straight away.

‍A Brief Look at Fuel Systems

Fuel systems differ greatly from plane to plane. Many high-winged aircraft rely solely on gravity for the fuel to reach the engine. But most modern planes house two fuel tanks with independent fuel pumps. These pumps are responsible for transferring the fuel from the tanks to the engine through complex plumbing, some more pumps, and a fuel control unit.

The pumps maintain constant pressure in the fuel lines to ensure that the engine gets the right amount of fuel depending on the rpm and the pilot's mixture settings.

Single Engine Aircraft

Smaller planes are usually powered by a piston engine and have a single fuel tank. But on modern planes, two tanks, one in each wing, are becoming increasingly common. A double tank system requires more components to control the amount of fuel reaching the single-engine.

The fuel is pumped from the fuel tank to a fuel selector valve. This control valve can allow fuel from only left, only right, or both fuel tanks depending on the settings made by the pilot. This little gadget allows the pilot to maintain a balance between both fuel tanks.

Small Twin Engine Aircraft

With the addition of an engine, the fuel system becomes increasingly complex. Features like in-tank pumps, a more complex indicator system, and cross-feed systems are found on multi-engine aircraft.

A cross-feed system allows fuel from one fuel tank to flow into the engine on the opposite side of the plane. Sometimes, the fuel goes directly to the engine, and in other planes, the fuel is fed into the opposite wing, making its way to the engine.

Turbo Props and Jet Engines

With the increase in the size of the aircraft, the complexity of the fuel system also increases. Larger aircraft often have multiple fuel tanks, automated fuel distribution systems, and a reliable indication and warning system.

Some of the prominent features on larger airliners include:

• Single Point Refueling – All tanks can be filled from a single filling point, usually located under the wing
• Multiple fuel pumps are installed to ensure proper fuel management even in the event of a pump failure
• The sophisticated warning and indication systems can give the pilot insight on the amount of fuel in each tank, total fuel remaining, amount of fuel used during flight, and fuel temperature.

The warning system can alert the pilot if anything is about to go wrong, like a drop in fuel pressure, low fuel, or fuel pump failure.

Reason for No Fuel Pressure

During a flight, there can be several reasons why a fuel system might lose pressure. Let us look at some of them

Fuel Leak

A fuel leak can occur anywhere along with the system. This means that a plane could be leaking fuel due to a ruptured tank, a broken fuel line, or even inside the engine. A leak will usually cause the pressure in the fuel lines to drop.

Fuel Imbalance

It is important to maintain similar levels of fuel in both tanks of the aircraft. If one of the tanks becomes considerably low compared to the other, it can lead to a fuel imbalance.  Improper refueling, engine failures, and poor fuel management can lead to an imbalance.

If one of the tanks becomes very low, the pilot will see a drop in the fuel pressure.

Mechanical Failure

If any of the pumps in the entire fuel management system fails, there will be less fuel flowing through the lines, and thus a drop in fuel pressure will be evident.

Frozen Fuel

Fuel temperature can be very critical for aircraft that fly at high altitudes for longer periods. As the plane is exposed to extreme temperatures, fuel can freeze in the lines.

The freezing point of every fuel depends on its specifications. However, for piston-powered and carburetor-equipped airplanes, icing can occur in the lines or even inside the carburetor.

Effects of No Fuel Pressure

If the fuel pressure is dropped due to a fuel leak, the pilot will have to identify the leak's location. A leak from one engine will force the pilot to shut the fuel supply to that engine in a multi-engine aircraft.

If the leak is in one of the tanks, the pilot will move the fuel to the other tank. Moving a lot of fuel into one tank and having the other tank empty can lead to difficulties controlling the aircraft. Landing becomes difficult as the plane will pull or sway to one side.

Fuel Starvation

Fuel starvation occurs when a plane has sufficient fuel onboard but cannot use it due to a fault in the fuel delivery system. Fuel starvation can occur because of all the reasons listed above. The consequences of starvation can be the following:

• Engine Failure: With no fuel reaching the engine, the engine will stop running, and with no power, the plane can turn into a glider
• Forced Landing: A faulty plane is much safer on the ground than thousands of feet above it. If the pilot detects the fuel system starting to fail, they will try to make a landing as soon as possible
• Controlled Flight into Terrain: If there are no landing sites nearby, the pilot will be forced to attempt a landing in a body of water or onto the terrain. In such an unfortunate scenario, the plane might come in contact with obstacles resulting in hull loss.