Mandatory Service Bulletin: B-25-001
Main Landing Gear Shock Strut Inspections
Release Date: December 21, 2011
To: All North American B-25 Owners and Operators:
Background: A B-25 aircraft has experienced failure of the Drag Arm, P/N 65081 (Item 6, Fig. 3), located at the top of the Bendix Pneudraulic Landing Gear Shock Strut, P/Ns 65929 (LH) or 65930 (RH). The Drag Arm is the attach point for the hydraulic retraction cylinder and the upper machined lug on the Drag Arm engages the downlock. The drag arm forging failed on landing, just below the retract cylinder attach point, resulting in a forward collapse of the main landing gear and significant damage to the aircraft. (See Figs. 1 and 2 for reference.)
Aircraft records did not indicate the last time any NDT inspections were performed on either main landing gear. As holder of the B-25 Limited Type Certificate AL-2, we are issuing this Mandatory Service Bulletin to detect any cracks at an early stage and prevent further Drag Arm failures.
Compliance Time: Within 90 days of issue date of this service bulletin and every 500 hours TIS thereafter.
Action: To prevent failure of the Landing Gear Shock Strut Drag Arm due to cracks, accomplish the following: All work to be accomplished in accordance with T.O 1B-25(J)-2.
1. Place the aircraft on jacks in accordance with T.O. 1B-25(J)-2.
2. Open the landing gear doors and gain access to the Drag Arm, P/N 65081 (Item 6, Fig. 3), at the upper portion of each Landing Gear Shock Strut.
3. Inspect for looseness of the Drag Arm in the Shock Strut by loading the main wheel fore and aft. The Drag Arm should be a tight fit in the top of the Shock Strut with no movement. Looseness in the strut is cause for replacement of the Drag Arm or the entire Strut. No repairs are allowed.
4. Disconnect the hydraulic retract cylinder shaft and secure out of the way. Clean and de-paint the area of the Drag Arm where the retract cylinder lug joins the Drag Arm and at the round retract cylinder attach eye. The part must be thoroughly cleaned as surface contaminates can prevent the penetrant from entering a defect. Clean part according to Dye penetrant kit instructions.
5. Using a red dye penetrant process that meets ASTM E1417, inspect each Drag Arm for cracks; pay particular attention to the upper and lower radius where the lug blends into the Shock Strut and where the round hydraulic cylinder attach eye blends into the lug. (See Fig. 4)
6. If cracks are found, replace the Drag Arm or the entire Shock Strut. No repairs are allowed.
7. Verify the spacer bushing is in place (P/N 4B14R10-28), reconnect the retract cylinder shaft and cotter pin the nut. Ensure the bolt head properly engages the anti-rotational notch on the side of the cylinder shaft. Apply grease at the Zerk fitting until the grease escapes the bushing.
8. Remove the battery access covers on the bottom forward area of each landing gear nacelle.
9. Retract the landing gear using the cockpit hydraulic hand pump or external hydraulic power.
10. Gain access to the machined downlock lug at the top of the Drag Arm through the battery door.
11. Clean and de-paint the machined area of the lug at the top of the Drag Arm. (See Fig. 4) The part must be thoroughly cleaned as surface contaminates can prevent the penetrant from entering a defect. Clean part according to Dye penetrant kit instructions.
12. Using a red dye penetrant process that meets ASTM E1417, inspect each lug for cracks; pay particular attention to the radius where the lug blends into the top of the Drag Arm.
13. If cracks are found, replace the Drag Arm or the entire Shock Strut. No repairs are allowed.
14. If no cracks are found, clean any NDT residue, prime and paint the Drag Arm to prevent corrosion.
15. Extend and lock the landing gear in the down position. Secure and safety the landing gear doors. Install the battery access covers.
16. Remove the aircraft from the jacks.
17. Record maintenance activity in airframe logbook and return aircraft to service.
Additional Inspections: Every 100 hours TIS or Annually, clean the above areas and, using a strong
light and a 10-power magnifying lens, inspect the above areas for cracks or corrosion pitting.
(See Fig. 4) Replace any unserviceable components.
Special Tools: Magnaflux® SK-3 or SK-416 NDT Dye Penetrant Kit or ASTM E1417 equivalent
Report results of initial inspection and discovery of any defective parts to:
S&R Aviation Services, Inc.
Attn: Tony Ritzman
c/o Aero Trader
7000 Merrill Ave #19
Chino, CA 91710
(909) 597-4020 V
(909) 393-0074 F
E-Mail to: Aerotrader@verizon.net
The Federal Aviation Administration requests the cooperation of all operators, mechanics and investigators in reporting a Malfunction Defect Report for all defects noted when accomplishing the above. Submit FAA Form 8010-4 (as revised) to your local FAA Flight Standards District Office (FSDO).
Replacement parts can be obtained from:
Attn: Carl Scholl
7000 Merrill Ave #19
Chino, CA 91710 USA
Phone: (909) 597-4020