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30 April 2007

TO: All Navion owners

SUBJECT: Fuel System Inspection

EFFECTIVITY: All Navion aircraft, Serial numbers NAV-4-002 through NAV-4-2561

REASON FOR Fuel valves have not been maintained in an airworthy
PUBLICATION: condition nor replaced when worn, resulting in some cases of leakage, loss of detents, and/or air ingestion resulting in loss of engine power. Internal leakage of some valves has resulted in fuel transfer between tanks.



A. Not later than 100 hrs. time-in-service (TIS) or 12 months, whichever occurs first, and thereafter at each 100 hr. or annual inspection, whichever occurs first, accomplish an inspection of the entire fuel system from the carburetor or fuel injection distributor aft to the engine driven fuel pump, electric fuel boost pump, fuel strainer, fuel valve (or valves in the case of aircraft altered with fuel transfer systems), all plumbing to original and auxiliary fuel tanks, and all installed fuel tanks.

B. Inspection will require opening cowling doors, removal of inspection plates under lower cowling, removal of left and right gill covers (aft of firewall), both front seats, left and right forward interior sidewall panels, left and right top access covers on wings just outboard of fuselage, and rock guard cover at aft end of nose wheel well.

C. Inspect all Aeroquip type hoses for age and condition. Inspect all rubber hoses between main tanks and fuel accumulator tank, and hose from accumulator tank to fuel selector valve for brittleness, cracking, or leaking. Inspect all rubber hoses in vent system under instrument panel, in both sidewalls of fuselage, and in top of wings for brittleness, cracking or leaking. Pay particular attention to the ¼" hose at right sidewall between firewall and vent system as on many aircraft return fuel passes through this line to the vent lines for return to the right main fuel tank. Replace any hoses that do not pass inspection.

D. Inspect all aluminum fuel lines for corrosion or abrasion damage. Replace as necessary.

E. Inspect for any fuel leaks and stains indicating seepage. On aircraft with tip tanks many of the lines are not visible so pay particular attention for fuel staining underneath the wings.

F. Initially no later than 100 hrs. TIS or 12 months, whichever occurs first, and thereafter at intervals of 300 hrs. TIS or 3 years, whichever occurs first, accomplish the following tests. Following the initial test the inspection interval may be increased to 500 hrs. TIS or 5 years, whichever occurs first if the fuel valve is replaced with a valve specifically listed in para. H, or the aircraft has received approval for a later style valve than the original equipment. Consult the ANS, Ltd. concerning specific valves.

      1. Accomplish one of the following, using extreme precautionary measures regarding handling of fuel.
                a. Disconnect negative battery terminal. Park aircraft on other than concrete surface and ground airframe to a suitable ground. Drain all fuel into fuel-approved containers. OR:
                b. Disconnect negative battery terminal. Ascertain that aircraft has used enough fuel from main tanks that the level is below one half so main inlet line may be disconnected without spilling fuel. Carefully cap lines to all auxiliary fuel tanks to prevent drainage.

     2. Inspect valve for ease of turning selector handle, positive detents, and any obvious fuel stains or seepage.

     3. Remove AN fitting from one port of the valve and measure orifice through valve with a ball gauge and micrometer. Minimum diameter allowed is .280" which is ID of AN-6 (3/8") fittings. Exception is allowed for Whittaker valves 6235-1/4D, and W7000-2D in use with E-185-3 or -9 engines (205 hp) as they were originally certified with these valves. The Whittaker valves must be replaced in aircraft with engines exceeding 205 hp as the orifices are undersize and are conductive to air intrusion at greater fuel flows.

     4. Reinstall AN fitting and cap all inlet lines to the valve. Perform vacuum test of fuel system from fuel selector to engine driven fuel pump.

               a. Disconnect outlet fuel line at fuel strainer (gascolator) and outlet line at fuel selector valve. Blow fuel from line with very gentle compressed air. Reconnect fuel line at selector valve.
               b. Connect hand-operated vacuum pump to line at gascolator outlet and apply 8.0" of vacuum. Note bleed down and verify that it does not exceed 1" over one minute. Repeat with fuel selector in all positions. If bleed down exceeds these limits, isolate the gascolator and fuel valve and test separately to determine where leak is occurring.
               c. For fuel valves serving more than one tank and to detect internal leakage, remove the cap from one valve inlet port and perform above vacuum test at outlet valve port for all positions of the valve except for the open line. Cap the open port, uncap another port and repeat test. Repeat for third port if present.
               d. With all inlet ports to valve capped, connect standard manometer to outlet of gascolator. Apply air pressure of 1.5 psi (equal to 3.06" of mercury or 41.6" of water) to the manometer and pinch off with a clamp. Should a drop in the manometer be noticed, check all connections and components with soapsuds to detect leak. Repeat for all positions of valve.
               e. For each fuel tank in aircraft, connect standard manometer to vent outlet of that tank leaving fuel lines capped at the selector valve. Be certain tank filler cap is sealing properly. Apply air pressure of 1.5 psi and pinch off with a clamp. Should a drop in the manometer be noticed, check all connections for leaks. If leak is isolated to a tank the tank must be repaired. See A. and B. below under REFERENCES section.

G. Reinstall items removed in PROCEDURE B.

H. If the valve fails any of the above tests it must be replaced with a new appropriate valve for the particular fuel configuration as specified in Reference C. or D. below, or in cases of approved modified fuel systems with a new valve of that type, or from the following list.

     1. ON-OFF valve for aircraft with baggage tank, no auxiliary fuel, or aircraft modified with fuel transfer systems.
               a. Navion part no. 145-48000-ANS1 (FAA-PMA pending) OR,
               b. Navion part no. 147-30013-201 (FAA-PMA pending) only approved with following modifications: Install with AN or NPT fittings in lieu of the banjo fittings which restrict fuel flow. Valve handle must be recessed in the middle cabin tunnel or protected by a shield to prevent damage from passenger's feet entering and exiting the cabin.

     2. MAIN-AUX-OFF valve for aircraft with underseat tank.
a. Navion part no. 145-48000-ANS2 (FAA-PMA pending) OR
Navion part no. 147-30013-202 (FAA-PMA pending) only approved with modifications listed in H., 1., b., above.

     3. LEFT-MAIN-RIGHT-OFF valve for all aircraft with 20 gallon tip tanks.
               a. Osborne Tank Co. part no. 4090 OR
               b. Navion part no. 145-48000-ANS3 (FAA-PMA pending) OR
               c. Navion part no. 147-30013-203 (FAA-PMA pending) only approved with modifications listed in H., 1., b., above.

. LEFT-MAIN-RIGHT-OFF valve for all aircraft with 34 gallon tip tanks.
               a. Navion part no. 145-48000-ANS3 (FAA-PMA pending) OR
               b. Navion part no. 147-30013-203 (FAA-PMA pending) only approved with modifications listed in H., 1., b., above.

I. Record in aircraft logbook that inspection required in PROCEDURES sections A, B, C, D, and E was accomplished with listing of any repairs required. Record in aircraft logbook results of PROCEDURES section F with dimensions obtained in F, 3, vacuum leakage noted in F, 3, c., and pressure leakage noted in F, 3, d, & e. If any valve is replaced in accordance with PROCEDURES section H, make an aircraft logbook entry listing part number of valve.


A. Navion Service Manual, First Edition A model Navion as revised January 1951, pages 77-79, and Figure 47.

B. Rangemaster Service Manual, Navion Aircraft Co., Harlingen, TX, pages 117-119, and Figure 53.

C. Navion Parts Catalog, Fourth Ryan Edition, September 1, 1952, pages 38-41C, 98-100, and 102-104.

D. Rangemaster Parts Catalog, Pages 56-70, and Figures 26, 27, 28, 29, 30, 31, and 32.

E. Navion Service Letter #87, dated February 20, 1965.


A. ANS, Ltd. Office: 360-833-9921

B. ANS, Ltd. Parts Department: 970-835-5096


May you always have tailwinds and deal with worthy people





Copyright © 2001 American Navion Society