Navy Landing Gear Perspective Tribaloy-Treated F/A-18C/D Main Gear Shock Absorber By Salvatore Piu August 2001 HCAT mtg

F/A-18A-D Main Landing Gear Tribaloy T-400 - Treated Shock Absorber Issue Proposed modifications Tests and flight evaluation Status

Issue Severe wear/scoring found on cylinder and piston at overhauls: Currently replace 100% Piston Rings (P/N 74A410855-2001/-7001) and Snubber Rings (P/N 74A410611-2001/-7001 Currently replace @ 90 % Piston Heads (P/N 74A410853-2003/-7001)

Shock Absorber Configuration P/N 74A410850-1009 Two stages Low pressure chamber, 150 psig, 8.87 inch stroke (shown in blue) High pressure chamber, 1265 psig, 4.25 inch stroke (shown in green) Total Stroke: 13.12 inches F/A-18C/D- shock absorber is not chrome-finished: Electrolysis-Nickel plating is used in stead of chrome.

Proposed Modifications Purpose: Reduce wear and internal damage of parts that typically get scrapped when worn -> increase time between overhauls Changes: Piston ring & snubber ring material change: from hard anodized aluminum to beryllium copper Piston head treated with Tribaloy SWA UHP-180 T-400 HVOF-deposited coating Tribaloy 400 Treated Area: Not the main piston area typically treated with Hard Chrome On an area where no previous coating applied

Piston head Piston Head Material: PH-13Mo Triballoy surface rides on bare 300M material (piston head is constantly in an “oil bath”)

Potential Benefits Increased MTBF Improved fleet readiness Longer component life Reduced overhaul costs Increased safety

Tests and Fight Evaluation Two shocks modified, S/N EMC 0632 & EMC 0635 Lab Tests Shock absorber ATP (service pressure) Load-stroke tests (verify consistency of static, load-stroke performance)

Tests and Flight Evaluation Flights Both shocks installed on product support plane (at Boeing, St. Louis, October, 1997): 23 flights (31 touchdowns) Performed post-flight load/stroke test (replaced leaking schroeder valve) Both shocks installed on one in-service aircraft (May 5, 1998) Request @ 30 CV arrested landings to provide meaningful data Flight clearance limited to 40 CV arrested landings Extended flight clearance to avoid interfering with fleet operations Right main landing gear experienced planing mechanism failure with EMC 0635 ( 60 field landings, 13 FCLP, & 80 CV arrested landings Removed both shocks immediately after planing mechanism failure

Tests and Flight Evaluation F/A-18A-D Planing Mechanism Function: plane the main wheel axle and compress the gear (shock absorber) to fit in the wheel well System has historical failures 8 primary components in system Improperly functioning shock is a suspect contributor to failures 8 Primary Components of F/A-18A-D Planing Mechanism are: Planing Link Knee Joint Bell Crank Assembly Connecting Link Shrink Link Upper Lock Link Lower Lock Link Crank (to axle) Over-Center Spring (to lock links)

Tests and Flight Evaluation Teardown inspection: shocks in excellent condition Goal reset by Navy: 200 CV landings Inspected, serviced, and placed shocks back on a fleet aircraft Shocks on various aircraft from May 99 to June 00 Modified shocks both participated in planing mechanism failures For each planing mechanism occurrence, shock removed from the failed gear, inspected, re-serviced, and placed on a fleet aircraft 5 on MLG’s with EMC 0635 (3 different MLG’s) 1 on a MLG with EMC 0632 (one of the MLG’s previously failed with EMC 0635)

Status Flight Evaluation Achieved 200 CV arrestments with one shock Personnel associate modified shocks with planing mechanism failures due to repeated participation In-service fleet evaluation halted by US Navy Teardown inspection: Wear observed was considerably less than would be expected (based on usage & compare to previous overhauled shocks)

Participated Planing System Failure Status Shock S/N Normal Field Landing Touch & Goes FCLP CV Bolter Field Arrestment Participated Planing System Failure EMC 0635 133 8 13 146 1 5 *1, *2 EMC 0632 137 12 54 200 *2, *3 Notes: EMC 0635 participated in 2 planing system failures, not included in qty (5), prior to Triballoy-associated modifications. Aircraft with modified shocks squawked for a pause in the stroking of the landing gear during landing (EMC 0635 lab tested for cause: nothing found) EMC 0632 exhibited slow to extend characteristics prior to modifications

S/N EMD 0635: Piston Head & Ring

S/N EMD 0635: Cylinder

Current Plan One Additional Flight Evaluation One aircraft with one new shock and and new-modified shock 200+ CV & FCLP landing Tear-down and compare both shocks If no issues found, implement change to spares and normal overhaul of existing shocks