STCs: The Key to a Successful Upgrade

Though complex to understand and highly technical in nature, it’s worth aircraft owners and operators taking the time to fully research Supplemental Type Certificates (STCs) to understand their implications for a planned upgrade.

STCs are issued by the US Federal Aviation Authority and come in all kinds of flavors – from those covering airframe modifications, to those allowing reconfiguration within the interior, to those allowing the aircraft to employ different performance limitations (such as an increase in gross operating weight). 

This can also allow a change of powerplant to achieve a longer Time Between Overhaul (TBO), better range or climb specifications, and/or reduced fuel consumption, etc — so there is a wide variety of STCs available.

Decoding the language used to promote the STC can be a challenge, since some of the terms are common to other types of work on the airplane, while others are exclusive to a particular STC.

Almost universally, however, aircraft STCs exist to correct a deficiency or improve an aspect of the aircraft’s performance and/or function, so it’s in the aircraft owner’s interest to learn their language.

Understanding an STC’s language is vital to identifying which one is best for achieving the desired goal, whether that’s improved performance, reduced fuel flow, longer TBO periods, or simply saving money when compared to undergoing an engine overhaul.

Currently, Blackhawk Aerospace is an industry leader in developing STC packages for Pratt & Whitney Canada’s PT6A-powered turboprop engines, while STCs also exist for Falcon jet engine upgrades, and Beechjet 400As. Such upgrades (and their related STCs) typically include more than a new engine, however, covering cowling, engine trend-monitoring, and new engine gauges.

And, at a time when passenger safety is at the forefront of everybody’s mind in relation to Covid- 19 transmission, Duncan Aviation, together with Dassault Aviation, recently developed STCs and installation packages for the Aviation Clean Air (ACA) ionization system for three pre-owned Dassault Falcon Jet models, including the Falcon 7X, Falcon 2000/2000EX, and Falcon 900/900EX aircraft (including all EASy variants).

While there is a multitude of STCs available for most aircraft make/models within Business Aviation, some of the terms accompanying STCs are not always clearly defined, and understanding them is key to making the most appropriate decision when shopping for the one that will provide the desired upgrade to your business airplane.

The Difference Between PMAs and STCs

On the one hand, Parts Manufacturer Approval (PMA) “is an approval granted by the FAA to a manufacturer of aircraft parts. The holders of a PMA are permitted to make replacement parts for aircraft, even though they may not have been the original manufacturer of the aircraft”.

The part produced under a PMA must comply with the quality-control and performance standards of the original part.

Conversely, as explained by the FAA, an STC is a Type Certificate (TC) issued when an applicant has received FAA approval to modify an aeronautical product from its original design and original type certificate. The STC, which incorporates by reference the related TC, approves not only the modification, but also how that modification affects the original design.

The benefits of the avenues provided by PMAs and STCs means aircraft can be upgraded and improved without the involvement of the original manufacturer, perhaps offering a path to alternatives that may cost less.

Before the FAA issues an STC allowing some kind of change to an aircraft, however, the applicant must produce documentation showing the effect of the installed STC on an aircraft. The STC applicant has the option (in most cases) of justifying their design by an engineering analysis, or by testing. 

If engineering analysis is chosen, a factor of 1.3 must be used as a safety buffer. Put another way, if the aircraft requires 9G forward-loading conditions for seats, then the engineering analysis must prove the design to be 1.3 times 9G, or 11.7G.

The design is frozen once it has cleared all obstacles and passed the engineering or testing requirements. Once the decision is made to proceed, the design is executed, and a prototype built (sometimes followed by several more iterations).

Selected Additional Terms Relating to STCs

Approved Model List (AML): AMLs are part of some aircraft STCs showing the different aircraft into which the STC can be installed. AMLs are typically developed and added to the STC after the initial approval by the FAA. The FAA reviews, and approves or rejects additions to the original STC.

Designated Airworthiness Representative (DAR): The FAA uses DAR as inspectors in lieu of sending FAA employees to inspect individual projects. 

A Designated Airworthiness Representative is an individual appointed in accordance with 14 CFR § 183.33 who may perform examination, inspection, and testing services necessary to the issuance of certificates. There are two types of DARs, including manufacturing (DAR-F) and maintenance (DAR-T).

Designated Engineering Representative (DER): A DER is an individual, appointed in accordance with 14 CFR § 183.29, who holds an engineering degree or equivalent; possesses technical knowledge and experience; and meets the qualification requirements of Order 8100.8.

DARs and DERs are often part of a company team developing STCs, PMAs, and new type certificates for their products.

Onus Remains with the Owner/Pilot

A Supplemental Type Certificate doesn't relieve a pilot or operator of their responsibility to operate the aircraft as approved by the FAA in the original Type Certificate, unless otherwise specified by the STC.

For example, if an aircraft is certified to a service ceiling of Flight Level 410, an engine STC giving that aircraft the capability to exceed that altitude doesn’t automatically allow it to use the higher altitude unless the STC specifically says so (that’s an issue involving the airframe and pressurization system).

The key to what the STC allows is in the documentation, which should be incorporated into the aircraft and engine logs.

We hope, from the preceding paragraphs, that the message rings clear. It’s important to both research and understand the STCs available for your aircraft, and also the terminology contained within. This will be the key to a trouble-free upgrade that delivers the capability and permissions you need.