AD 49-15-03

49-15-03 BEECH: Applies to All Models C18S and AT-11 Aircraft Equipped With: (1) Nose Fuel Tank or (2) Wing Fuel Tank Vents Which Discharge Below the Wings.

Compliance required not later than next annual inspection.

As a result of fuel or vapors discharged from fuel tank vents entering the tail wheel well, fuel fumes in hazardous concentrations may collect in the airplane's cockpit and cabin. To preclude this condition, the following must be accomplished:

(1) If the airplane is equipped with a nose fuel tank, install adjacent to the fuel tank selector valve a suitable placard which reads "Use Nose Tank for Warm Up -Take-Off on Main Tanks -At Safe Altitude Use Nose Tank."

(2) On airplanes with wing tank vents extending below the wing, accomplish either 2(a) or 2(b) or 2(c).

(a) Using an adequate tube splice, extend the rear fuel tank vents to a distance of 7 inches below the wing skin. The ends of these vents are to be scarfed at 45 degrees with the scarfed surface facing aft.

(b) Relocate the outlet end of each rear tank vent to a point approximately 27 inches outboard of its present position.

(c) Install a suitably designed fabric or equivalent fumeproof panel over the opening of fuselage bulkhead No. 12 to act as a draft barrier.

(3) If the wing fuel tanks are equipped with two vent systems (one system having the vent outlet below the wing and the other, above) the system with the vent outlet below the wing should be removed from the rear tanks unless item 2 is complied with.

(Beech Service Bulletin No. C18-10 dated January 31, 1949 covers this same subject.)