Garmin GTX 335 w GPS Installation Guidance page 57

Modification of Avionics Stack Mounting Rails
Existing mounting rails can contain holes from previously installed equipment. If existing rail holes do not
match holes in the GTX 335 mounting rack, it is permitted to modify the rails through the addition of
fastener holes to accept installation of the mounting rack. If more fastener holes are required, the following
conditions should be adhered to:
Maintain a distance at least 2 X D from the edge of the rail for the other fastener holes.
Maintain at least 3 X D distance between holes when adding holes among the existing holes.
If existing brackets or mounting rails are found to be incorrect for installation of the GTX 335, new parts
need to be fabricated. In some cases, there can be too many holes from previous avionics mounting tray
installations. If new parts are to be fabricated, adhere to the following conditions:
Remove existing mounting rails or brackets from instrument panel. Avoid enlargement of existing
rivet holes.
Fabricate new parts as close to the original design as possible (extrusion or sheet metal). Use the
same material thickness and type with only the holes necessary for the planned avionics stack.
If material type of the original rails or brackets is unknown, replace with 2024-T3 (bare or Clad)
aluminum of the same thickness as the original part. Use sheet metal techniques (bend radius,
fillets, etc.) applicable to material type and thickness.
Make sure fabricated parts are protected from corrosion. Apply epoxy primer that meets MIL-P-
23377 Class N, or other corrosion protection methods listed in the aircraft's maintenance manual.
Area around the fastener holes on the side of the fabricated rail that attaches to the GTX mounting
rack must be cleaned and prepared for electrical bond per section 3.15.1.
Install fabricated mounting rails to instrument panel. Use the same number and size of rivets as
original rivets removed.
190-00734-17
Rev. 1
GTX 335 w/GPS Installation Guidance
Page 4-5