2.6 Type Certificate Data Sheets (TCDS), STCs, ACs & Maintenance Manuals

2.6 Type Certificate Data Sheets (TCDS), STCs, ACs & Maintenance Manuals

Every aircraft operating in civil aviation is built and maintained against a rigid hierarchy of technical publications. A practicing aviation mechanic must be skilled in navigating and interpreting Type Certificate Data Sheets (TCDS), Supplemental Type Certificates (STCs), Advisory Circulars (ACs), Manufacturer Maintenance Manuals, and the ATA 100 / iSpec 2200 numbering system.

1. Type Certificate Data Sheets (TCDS) and Aircraft Specifications

When a manufacturer designs a new aircraft, engine, or propeller, the FAA evaluates the design against airworthiness standards (e.g., 14 CFR Part 23, 25, 27, 33, or 35). Upon successful certification, the FAA issues a Type Certificate (TC) and publishes the Type Certificate Data Sheet (TCDS) under 14 CFR Part 21.

                        KEY CONTENTS OF A TCDS / AIRCRAFT SPEC
  ┌────────────────────────────────────────────────────────────────────────┐
  │ 1. MODEL DESIGNATIONS & CERTIFICATION BASIS (e.g., Part 23 / CAR 3)    │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 2. ENGINE & PROPELLER COMBINATIONS (Approved models, ratings, limits)  │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 3. AIRSPEED LIMITATIONS (Vne, Vno, Va, Vfe in KIAS/KCAS)               │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 4. CENTER OF GRAVITY (CG) RANGE & DATUM LOCATION                       │
  │    - Forward and aft CG limits, leveling means, empty weight CG limits │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 5. FUEL & OIL CAPACITIES                                               │
  │    - Total capacity, usable fuel, unusable fuel weight and arm         │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 6. CONTROL SURFACE DEFLECTIONS (Travel limits in degrees ± tolerance)  │
  ├────────────────────────────────────────────────────────────────────────┤
  │ 7. MANDATORY PLACARDS & MINIMUM CREW REQUIREMENTS                      │
  └────────────────────────────────────────────────────────────────────────┘

TCDS vs. Aircraft Specifications

• Aircraft Specifications: Documents issued prior to 1958 under the Civil Aeronautics Administration (CAA) for aircraft certificated under the Civil Air Regulations (CARs, such as CAR 3). Aircraft Specifications contain essentially the same technical data as modern TCDS.
• Type Certificate Data Sheets (TCDS): Documents issued by the modern FAA for aircraft certificated under Title 14 CFR.

Exam Fact: The TCDS is the ultimate authority for control surface travel limits, approved propeller diameter ranges, leveling means, and datum location. If there is a discrepancy between an aftermarket maintenance guide and the TCDS, the TCDS governs.

2. Supplemental Type Certificates (STCs)

Under 14 CFR Part 21 Subpart E, any person who alters a product by introducing a major change in type design that is not great enough to require a new application for a type certificate must apply for a Supplemental Type Certificate (STC).

• An STC represents FAA-approved data for that specific modification (e.g., installing a more powerful engine, adding winglets, converting to a glass cockpit avionics suite, or installing a cargo door).
• Permission to Use: Under 14 CFR § 21.120, an installer must have written permission from the STC holder to use the STC on a specific aircraft.
• Instructions for Continued Airworthiness (ICA): Under 14 CFR § 21.50(b), the holder of an STC must furnish at least one complete set of ICAs to the aircraft owner. These ICAs become part of the aircraft's permanent maintenance program.

3. FAA Advisory Circulars (ACs)

The FAA issues Advisory Circulars (ACs) under 14 CFR to provide guidance and acceptable methods in various aviation subjects. The numeric subject system corresponds to the FAR parts (e.g., AC 20 is General; AC 39 is Airworthiness Directives; AC 43 is Maintenance; AC 65 is Certification).

AC 43.13-1B and AC 43.13-2B

• AC 43.13-1B (Acceptable Methods, Techniques, and Practices — Aircraft Inspection and Repair): The "bible" of standard aviation maintenance practices. Contains acceptable methods for safety wiring, sheet metal riveting, electrical wiring, wood structures, fabric covering, and non-destructive testing (NDT).
• AC 43.13-2B (Acceptable Methods, Techniques, and Practices — Aircraft Alterations): Provides acceptable methods for structural alterations, radio installations, antenna mounting, and tow hitch installations.
• Legal Status: AC 43.13-1B/2B constitutes acceptable data, not approved data. It may be used as approved data for major repairs only when explicitly authorized by the FAA Administrator, an ASI Field Approval, or relevant FAA policy.

4. The ATA Spec 100 / iSpec 2200 Standardization System

The Air Transport Association of America (ATA) developed Specification 100 (now modernized as iSpec 2200) to standardize technical documentation across all manufacturers and aircraft types. Every maintenance manual, illustrated parts catalog, and wiring diagram follows this standardized chapter numbering format.

Comprehensive ATA Chapter Numbering Reference