Field Approvals & Supplemental Type Certificates (STCs)

The following subjects are covered in this overview of the process to obtain an STC:

  • Regulatory Basis
  • Key Documents
  • STC Process
  • STC Variants
  • Coordinated Field Approvals

STC Regulations & Policies

Relevant Rules

The FAA's rule for classifying type design changes is Part 21.93 in Subpart D.

Subpart E also refers to Part 21.93 in establishing applicable regulations for an STC applicant. If the TC holder is making the change, data is a change to type design as identified in Part 21.97.

In the case of an STC, there is no reference to type design; instead, Part 21.115 calls for the substantiating data to show that the altered product meets applicable airworthiness requirements.

Regulatory Basis

  • Part 21 Subpart E - Supplemental Type Certificates
    • Part 21.113 permits major changes by persons other than the holder of the type certificate
  • Part 21 Subpart D - Changes to Type Certificates
  • Part 21 Subpart B - Type Certificates
    • type certification procedural requirements

Key Documents

Advisory Circular (AC) 21-40 provides a single national reference to show FAA's expectations for how a complicated STC project should be conducted. Also, the quality of the technical data and documentation package is highlighted in the AC.

  • AC 21-40, STC Application Guide
    • Provides detailed administrative, procedural, and technical guidance for conducting complex STC projects
    • Data — Provides guidelines and samples for quality of drawing package and other technical data documentation (Chapter 5)
  • Order 8110.4, Type Certification (PDF)
  • FAA Order 8110.4, STC Process -
    • Major Steps as required
      • Applicant Applies for STC
      • Familiarization and Preliminary TC Board Meetings
      • FAA Develops Certification Program Plan
      • FAA Establishes Certification Basis
      • Applicant Submits Data for Approval
      • FAA Design Evaluation
      • FAA and Applicant Hold Specialists and Interim TC Meetings As Required
      • FAA Performs Conformity Inspections
      • Engineering Compliance Determinations
      • Pre-Flight TCB Meeting
      • Applicant Performs Ground Inspections, Ground Tests, and Flight Tests
      • FAA Reviews Manufacturer's Flight Test Results and Issues TIA
      • FAA Performs Conformity Inspections, Witnesses Tests, Performs Official Certification Flight Tests and Flight Standards Evaluations
      • Functional and Reliability Testing
      • FAA Approves Flight Manual Supplement or Supplemental Flight Manual and Holds Final TCB Meeting
      • AEG Completes Continuing Airworthiness Determination
      • FAA Issues STC
  • An STC will not be issued to:
    • approve minor changes, or for approval of identical replacement parts (unless the installation of such parts constitutes a major change to the type design);
    • approve design changes to TSO approved articles unless the TSO is invalidated for the modified article. An STC which modifies a TSO article must provide for installation;
    • combine two or more STC's without additional showing of compliance; or
    • manufacturers or applicants outside of the U.S. (Except as provided for in a bilateral agreement).
  • Establishment of Certification Basis:
    • Same as for a change to type design.
    • 14 CFR 21.115(a) Applicable requirements
      • Each applicant for a supplemental type certificate must:
        • Show that the altered product meets applicable requirements specified in 14 CFR 21.101 and,
        • In the case of an acoustical change, show compliance with the applicable noise requirements of 14 CFR part 36 and,
        • In the case of an emissions change, show compliance with the applicable fuel venting and exhaust emissions requirements of 14 CFR part 34.
  • An STC will be issued only if:
    • the pertinent technical data have been examined and found satisfactory,
    • all necessary tests and compliance inspections have been completed, and
    • the alteration has been found to conform with the technical data.
  • STC Compatibility Examination - 1
    • A new design change should be compatible with related previous design changes. Reliance on any previously approved changes should be described in the approved data.
  • STC Compatibility Examination - 2
    • FAA approval of a new design change may require coordination with the accountable FAA Directorate office. For some elaborate changes, the FAA project office must coordinate with the FAA office responsible for the type certificate of the aircraft being changed.
  • Imported Product
    • Proposed STC's to import products may require consultation with the foreign CAA of the State of Design.
    • The Aircraft Certification Office (ACO) should determine if the complexity of the STC requires consultation with the Civil Aviation Authority (CAA) and should coordinate their involvement through the appropriate Certificate Management ACO - certificate management standards staff.
  • Additional responsibilities of STC Holder:
    • Report failures, malfunctions and defects (14 CFR § 21.3)
    • Make TC Available to FAA and National Transportation Safety Board (14 CFR § 21.49)
    • Make Instructions for Continued Airworthiness available to owner/operator (14 CFR § 21.50)
    • Make required design changes to address Airworthiness Directives and make them available (14 CFR § 21.99)
    • Make flight manuals supplements and supplemental flight manuals available with each alteration (14 CFR § 21.5 & § 23.1581)

STC Variants One-Only

  • An STC may be issued as a “one-only” for a particular aircraft by make, model, and serial number. A “one-only” STC cannot be amended and the holder is not eligible for issuance of any production approval. All subsequent approvals of the modification must be handled via a multiple STC.

STC Variants No-Hazard

  • A non-interference or no-hazard STC addresses a modification that provides a convenience function that is not required by the applicable airworthiness standards. The STC “Limitations and Conditions” section includes limitations of the extent of the FAA approval.



Forms used in the STC process

  • Reference Advisory Circular 21-40 (PDF), Application Guide for Obtaining a Supplemental Type Certificate, Appendix 7
  • Order 8110.48 (PDF), How to Establish the Certification Basis for Changed Aeronautical Products
  • Forms

Other Documents used in the STC process

  • Orders
  • Advisory Circulars
  • Policy
    • Memorandum
    • Notices
    • Letters
  • Type Certificate Data Sheets
  • Supplemental Type Certificates
  • FAA aircraft website

Coordinated Field Approval

  • Request from Flight Standards Inspector for the ACO to provide technical assistance for a field approval.
  • Usually based on complexity of the modification
  • Not an STC
  • Order 8900.1, Flight Standards Information Management System (FSIMS), formerly Order 8300.10, specifies those types of alterations that may be approved, under specific conditions, for field approval. This reference also lists those types of alterations that must either be evaluated by the FAA engineering department or the STC process.
  • Visit the Flight Standards Information Management System (FSIMS) for more information.
Last updated: Wednesday, June 29, 2022