What is an STC?

What does the term “supplemental type certificate” or “STC” mean and why is it important?

When an aircraft is certified by a regulator such as the FAA or EASA in Europe, the manufacturer is issued a “type certificate” for the aircraft, by the regulator. Engines also get a separate type certificate because they require stringent testing before being approved.

Essentially, once a type certificate is approved, everything that is part of the aircraft is also approved, though there are always exceptions such as some products requiring special testing such as avionics/electronics.

Let’s say an aircraft manufacturer delivers a new long-range jet. And then later decides to modify it by adding a satellite communications system. The manufacturer can do so by simply putting it on the aircraft and making the connectivity system part of the type certificate for that aircraft, and then it can install those systems in all the new jets and the ones it previously delivered.

However, suppose that same manufacturer wants help doing all those installations, and wants to have that communications system available for other models, and also available for other service centers to install?

Here is where the STC comes in. It’s a “supplemental type certificate,” which means an addition or modification of the original type certificate. The regulator allows this so that aftermarket companies or even OEMs (original equipment manufacturers) can make a change to the original aircraft design without having to redo the type certificate. That’s what “supplemental” means.

In fact, the original manufacturers don’t have any say in whether a company can develop an STC for the OEM’s aircraft.

That’s a great feature of the aviation regulatory landscape, allowing for innovation to come from a variety of non-OEM sources.