# AD 56-21-02: Spar Deterioration - Type: Airworthiness directive - Status: Current - Products: Cessna T-50 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Small airplane - Registered aircraft: 37 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/2367A9DA5415AE1886256A340061EB72.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/56-21-02 ## The airworthiness directive 56-21-02 CESSNA: Applies to All Model T-50 (AT-17 Series and UC-78 Series) Aircraft. Compliance required on or before the next periodic inspection but not later than January 1, 1957, and at each periodic inspection thereafter. Receipt of reports of spar deterioration subsequent to the corrective measures of AD 49- 20-01 necessitates repetitive and detailed inspections. It is therefore requested that the rear spar just outboard of the fuselage fittings in the area of the inside corner of the fuel tank compartment be inspected annually for indications of wood deterioration of the spar. To accomplish the inspection, remove a section of plywood wing covering 6 inches x 4 inches adjacent to and outboard of the rear spar fuselage fittings and/or remove the fuel tank. If the inspection reveals any evidence of deterioration or separation of glue lines, removal of the lower cap strip between ribs in the affected area for detail inspection is required. To facilitate periodic inspection a permanent inspection opening may be incorporated provided it is reinforced to maintain strength equivalent to the original panel. If spar deterioration does not exceed 1 inch of spar depth the spar may be repaired by the following method: Remove the damaged wood of the spar and fit with a matched inlay by gluing to the spar with the ends of the inlay tapered in a ratio of no less than 15 to 1. A bottom reinforcing strip or plate of an approximate thickness of 0.4 of the depth of thickness of the inlay with a maximum of 0.4-inch thickness is to be matched and glued to the bottom surface of the spar. This bottom reinforcing strip should extend approximately 3 inches beyond the end of the glue line of the inlay strip. The installation of this reinforcement plate may require a rework of the spacer block at the attachment fitting and a rework of the fore and aft stringers where they attach to the bottom surface of the spar. The following contingencies apply in the repair of the spar: (1) In the "5,700 pound" wing spar, the material for the inlay lamination and bottom reinforcement strip or plate should be fabricated from birch, maple or its equivalent. (2) In the "5,100 pound" wing spar, the material for the inlay lamination and bottom reinforcement strip or plate may be fabricated from spruce. Workmanship, gluing process, quality of materials and other limitations and repair requirements of CAM 18 apply except where otherwise noted. After completion of the spar repair and repair or replacement of deteriorated gussets, stringers, etc., as necessary, drain holes should be incorporated in wings if not already installed. If the drain holes are installed it should be ascertained that they are open. The felt padding under fuel tanks should be inspected for evidence of absorption of moisture, and the padding replaced, if necessary, with neoprene coated felt or equivalent nonabsorbing material. This supersedes AD 49-20-01. ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS A-722](https://openairdocs.org/tcds/A-722): Cessna Aircraft Company; names 1 of 1 models: T-50 (Army AT-17 and UC-78 series; Navy JRC-1) ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 37 (37 by airframe model, 0 by engine model) - Makers: Cessna 37 Models with the most aircraft: - [Cessna T-50](https://openairdocs.org/model/cessna-t-50): 37 aircraft (airframe model) All 1 models: https://openairdocs.org/ad/56-21-02/models.md Every aircraft: https://openairdocs.org/ad/56-21-02/aircraft.md Its text cites no advisory circulars or STCs. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.