21JDesign Organisation Approval [DOA] under EASA Part 21

Aircraft modifications require airworthiness compliance.

SII Netherlands over the years has aquired specialization in aircraft certification. With our engineering and certification office we are able to supply the full development range to the customer.
We are authorised to act in airworthiness issues on behalf of customers for aircraft modifications. These modifications range from minor and major structural modifications to acquiring the Supplemental Type Certificate (STC). Many aircraft equipment manufacturers, airlines and aircraft conversion projects have used this unique service.

Feel free to challenge our engineers, with your modification requests.

Our DOA team consists of certifed and qualifed people experienced in various technical disciplines ranging from:

  • Cabin interiors;
  • Equipment qualification & integration;
  • Cargo compartment modifications;
  • Fuselage structure;
  • Special mission aircraft


Download here our EASA Terms of Approval