Separate vent lines are provided for each tank and are sized to accommodate the maximum airflow rates during flight or when refueling. Fuel entering the vent system during transient maneuvers is caught by the surge tank and drawn back into the fuel tanks when stable flight is resumed. A pipe extending from the outboard end of each tank to the surge tank in the opposite wing provides the venting during refueling, level flight and descent when the airspace is located at the outboard end of the tank. The vent lines terminate in surge tanks formed between ribs 17 and 18 in each wing. The vent lines connecting each tank to the NACA air scoop/inlets intake tank are open, and oriented upwards, without intervening valves or other potential obstructions and are sized to accommodate the maximum airflow rates during flight or refueling without exceeding tank pressure limitations. The vent pipes that vent to the opposite tank have two outlets within each surge tank which are oriented downward. They also are at different distances from the wing skin, in order to minimize the risk of blockage.

At the wing root in each tank, a float-operated vent valve is 'teed' into the vent line to provide venting during noseup conditions or if refueling with the aircraft standing across sloping ground when the airspace could be located at the inboard end of the wing. Vent holes through the top of the ribs provide a clear vent path from the outer end of the tank to the inner end in order to accommodate the rapid transfer of air that takes place during takeoff and initial climb. The float valve closes when fuel in the main tank lifts the float. This prevents the entry of fuel into the vent lines. When there is no fuel to lift the float (during climb), the float valve opens. This ensures that the vent float valves at the root open quickly to allow fuel to drain into the wing tank thereby minimizing the amount of fuel entering the surge tank.

The surge tank check valve provides a secondary vent path into each fuel tank if the main vent line is obstructed/blocked. A spring-loaded check valve is located at the outboard end of each fuel tank at rib 17 to give a direct path from the surge tank into the adjacent fuel tank. The surge-tank check valve is a flapper-type valve. It has a body with attachment flange and a spring-loaded flap. The check valve is only required to operate if the main vent line is obstructed/blocked. This vent arrangement ensures that no single blockage can prevent a tank from being vented to atmosphere.

A rubber non-return drain valve (bladder vent valve) is installed at the low points of each main vent line (2 each). This drain valve allows any fuel or water which collects in the vent lines to drain back into the main fuel tank. When the fuel tank level is above these vent bladder valves, the bladder will collapse thus restricting the fuel to flow in the reverse direction and into the vent system.

Two NACA scoop/inlets are installed on the lower surface of each wing. The vents in the NACA scoop/inlets supply ram-air to the vent system when the aircraft is in flight and air flow to the fuel tanks when the aircraft is on the ground.

The vent system arrangement ensures that no single blockage can prevent a tank from being vented. The ends of the vent lines are turned down so that fuel in the surge tanks is drawn back into the wing tanks by the vacuum caused by fuel consumption.

A line extending from the outboard end of each wing tank to the surge tank in the opposite wing lets the air flow freely during refueling, level flight and descent. The vent float valves in the wing root of each tank let fuel go from the vent lines back into the wing tank. The vent float valves also supply airflow during noseup conditions or when refueling with the aircraft positioned across a slope, where the airspace in the wing tanks could be at the inboard end of the wing.

Vent holes through the top of the ribs in each wing tank give a vent path from the outer end of the wing tank to the inner end. This lets air move from wingtip to root during takeoff and initial climb. The vent holes ensure that the vent float valves at the root open quickly and any fuel spilled into the surge tank is minimized.

When fuel spills into the vent system during transient maneuvers, it is caught by the surge tank and drawn back into the fuel tanks when stable flight is resumed. The surge tank check valves give a secondary vent path into the related wing tank.

The bladder valves prevent fuel leakage through the NACA scoop/inlet when the aircraft is parked on a slope with more than 1 degree of roll. The bladder valves drain the fuel in the main vent lines to the related wing tank.

The vent system supplies ram air through the NACA scoop/inlets installed on the lower surface of each wing. When the aircraft is in flight the fuel tanks have a small positive pressure on the NACA scoop/inlets. When the aircraft is on the ground the vent system lets air pressure to release out of the fuel tanks during refueling operations and lets the thermal expansion of the fuel stored in the fuel tanks thorough the NACA scoop/inlets.