In Wing Fuel Tank Kit Advisory - Mar 20, 2004

Applicability: Users of Chinook Plus 2 aircraft with optional in-wing tanks

Effective: immediately

Purpose: This memo is designed to advise users of Chinook Plus 2 supplementary in-wing tanks on updated operational limitations.

Background: The in-wing fuel tank option is popular with Chinook owners for extending the endurance of their aircraft, more than doubling total fuel capacity versus strut tanks alone.

The in-wing tanks are mounted above the wing drag/anti-drag braces and below the wing ribs with the root ends visible inside the cabin. Fuel leaves the tanks via two points on the root end of the in-wing tank, one located at the front and one at the rear of the tank.

The in-wing tanks have always been marketed as supplemental to the strut-mounted tanks. As of this writing, there has been only a single Chinook Plus 2 sold without the standard strut-mounted fuel tanks. The original builder of this aircraft elected to substitute the in-wing tank kit for the strut tanks for aesthetic reasons. During the course of his flying, no adverse effects of using these tanks were experienced.

Source of the Advisory

The aircraft was subsequently sold to a flight training unit to be subjected regularly to stalls, steep turns, extended climbs and descents and side-slips.

Prior to use in the training environment, it was determined in certain flight attitudes the fuel pickup points of the in-wing tanks could be exposed to air, allowing air to be drawn in to the fuel lines.

This occurred with less than full tanks; the exact amount of remaining fuel was unknown. The condition was noted as bubbles appeared to travel from the in-wing tanks along the fuel lines. This could eventually have led to the float bowls emptying sufficiently to starve the engine of fuel. Returning the aircraft to a straight and level attitude while the engine was running would allow fuel to cover the pickup points and re-fill fuel lines.

Procedure Change

Chinook owners are advised to use in-wing tanks for level cruise flight only. During take-off or landing or any flight attitude where fuel could be drawn by gravity away from the front or rear root end fuel pick-ups, the in-wing tanks should not be used as a fuel source. Instead, the standard strut-mounted tanks with integrated flop tubes should be used.

Conclusion

By following this procedure, the in-wing tanks may continue to be used as they were intended: as supplemental tanks for extending the Chinooks endurance.