S4A is an experienced aeronautical engineering company, granted as Part 21-J DOA by EASA. Established in 2007, we provide integral solutions to our customers. We work worldwide, based in Madrid (Spain). S4A is the first aeronautical engineering company in Spain to be granted with this certificate by EASA. Our services include minor and major modifications and repairs in cabin safety, structures, avionics, electrical systems and environmental control systems. We also get EASA certifications for STCs, and EASA / FAA validations. Additionally, we offer consulting and CVE services for aircraft modifications and upgrades, quality assurance system implementations and airworthiness management.