About Our Aviation Engineering Services
Our aviation engineering services hold a Part 21 Subpart J DOA enabling it to certify UKCAA approved STCs and Major Repairs. Additionally, where a design change or repair is classified as minor, STC Twenty One Limited is authorised to approve them under the DOA using approval reference UK.21J.0198 through CAA.
Company History
STC Twenty One Limited was founded by John Dent and Peter Gaughan in the roles of Technical Director and Managing Director respectively.
The foundations of STC Twenty One Limited begin with Aero Engineering Design Limited (AED). CAA Approval Number AD/1769/89
AED was founded in 1988 by John Dent and was a UK CAA Approved Design Organisation prior to the inception of EASA.
STC Twenty One Limited continues to support the wide and varied customer base cultivated by AED since 1988 and is responsible for continued airworthiness support for all approved modifications issued prior to September 2003.

Core Values
- Safety is our top priority.
- Communication – Communication – Communication.
- Flexibility but with due diligence.
- Professionalism, integrity and honesty.
- Equal opportunities for ALL staff members.
- Customer satisfaction for ALL our customers.
- That hard work and customer satisfaction yields a healthy business.
- Work together to recover from set backs.
- To embrace change and move with the times.

Aviation Engineering Services Team
STC Twenty One employs a highly experienced and respected team of professionals comprising of the core team members below. In addition we have access to a wider network of professionals including aerodynamicists, flight test/performance engineers and flight test pilots experienced in both fixed and rotary wing aircraft types.
Commercial Team
Quality Team
Mechanical & Structures Team
Avionics Team
Technical Publications Team
Aviation Engineering Services Support Team
UK CAA Approved Design Organisation
STC Twenty One
All aircraft modifications and aircraft repairs are managed by our UK CAA approved Design Office represented by STC Twenty One (UK.21J.0198).
What We Offer
Aviation Engineering Services
STC Twenty One Limited holds a Part 21 Subpart J DOA enabling it to certify UK CAA approved STCs and Major Repairs. Additionally, where a design change or repair is classified as minor, STC Twenty One Limited is authorised to approve them under the DOA using approval reference UK.21J.0198 through CAA.
Our employees are spread across our Avionics, Mechanical, Quality and Commercial Teams with a high level of experience and certification enabling the company to perform specialised services on engines and aircraft. Read more about our Services.