Supplemental Type Certificates
Twisted-Wrench LLC  Aircraft Maintenance Special Projects
A supplemental type certificate (STC) is a type certificate (TC)
issued when an applicant has received FAA approval to
modify an aircraft from its original design.  The STC, which
incorporates by reference the related TC, approves not only
the modification but also how that modification affects the
original design.
Where can I find information about STCs installed on my

If you need information about supplemental type certificates
that have been installed on your aircraft, you may:

  • Search the Supplemental Type Certificates database in
    the on-line Regulatory and Guidance Library, or

The maintenance provider will record the installation of a
STC by:
  • Adding an alteration entry in the aircraft records that
    complies with 43.9
  • Completing and distributing FAA Form 337 per 43
    Appendix B
  • Per 21.120 and 91.403(d) written permission from the STC
    holder is obtained and (opinion) filed with the 337
  • Updating the Equipment List as required
  • Updating the Weight and Balance as required
  • Adding the Flight Manual Supplement as required
  • Giving any Equipment Operating Manuals to the owner

The regulatory requirement for STC Permission was
added to the regulations in 2006.

Previously installed STCs were not exempted from this

Prior to this change, a copy or the cover sheet of the STC
should have been in the records with the FAA Form 337.