STCs, MRAs & TSOs: What Jet Owners Should Know

Do you understand the intricacies of Supplemental Type Certificates? There are some basics that an aircraft owner needs to know before electing to upgrade their business aircraft, as outlined here…

Some owners of business aircraft whose careers aren’t closely tied to the aviation industry use aircraft management companies to handle the complexities of operating and maintaining their aircraft, ensuring the aircraft is available to fly immediately when required.

Others choose either to set up their own Flight Departments to handle the vital administrative activities necessary to keep their aircraft in airworthy condition and operationally ready at very short notice – or have the pilots they employ to fly their aircraft perform those admin activities or arrange for the activities to be handled by third parties.

Basically, non-aviation business aircraft owners don’t need to know much about the activities needed to keep their aircraft airworthy for flight at any time, say Tracy Bohaboj and Kelly Sepe, highly experienced aircraft and airworthiness certification engineers who work for Duncan Aviation and Flying Colours, respectively.

As a result, many owners know little to nothing about the important technical concepts and terms underpinning the airworthiness and operational regulatory basis governing their aircraft. All they are usually concerned about are the costs involved in owning and operating their aircraft, and the costs and time required when their aircraft and engines require maintenance or undergo modification or upgrade work.

But even if ownership, operating and modification/upgrade cost, and operational downtime are all an owner cares about regarding his or her aircraft, Bohaboj and Sepe reckon it’s advisable for the owner to know a few basics about the regulatory basis governing the aircraft – particularly regulations covering modifications and upgrades.

Only by doing so can the owner comprehend fully the implications in cost and downtime of having an MRO facility perform the documentary and parts research and the work needed to modify or upgrade the aircraft – and ensure that after the work is completed the aircraft is officially in fully airworthy condition, meeting all regulatory requirements.

Knowing in advance the basic regulatory governance and the common terms and abbreviations for important regulatory concepts required when modifying or upgrading an aircraft will help an owner ask their chosen MRO facility the right questions – and obtain fully informed, clear answers – when planning to have mods or an upgrade performed.

STCs: Why They Are Important

The most important thing of which an owner should be aware before authorizing work to begin on modifying or upgrading their Business Aircraft is if the work will need to be covered by one or more Supplemental Type Certificates (known as an STCs) in order to be performed.

If it does, and the owner decides for reasons of cost and aircraft downtime not to agree to have the STC(s) developed and certified but authorizes the modification or upgrade to be performed anyway, then the owner will not be able to operate his or her aircraft until the relevant STC(s) are developed for the specific installation(s) in that aircraft type.

Reputable MRO facilities wouldn’t allow the customer to make that decision and would not proceed with the work, citing the aircraft’s subsequent indefinite grounding as the reason why.

An STC is additional to the basic airworthiness Type Certificate covering an aircraft. For regulatory purposes it confirms that any new equipment added to an aircraft, or replacing equipment which was originally installed, meets the regulating authority’s airworthiness criteria for that aircraft type, as specified in the aircraft’s Type Certificate Data Sheet (TCDS).

The relevant authority’s formal certification approval of any STC involved in modifying or upgrading an aircraft is required for the STC to be granted.

According to Sepe and Bohaboj, an STC is typically needed when addition or replacement of equipment could modify or affect an aircraft’s flight characteristics; the pilots’ ability to control the aircraft; the ability of the aircraft’s flight deck to receive and transmit communications; and the operation of (and interaction between) the aircraft’s systems.

Adding a new cabin and/or flight deck satcoms communications system is a prime example of a modification that requires an STC to be approved by the airworthiness regulating authority, for instance.

Usually, every different aircraft type requires a type-specific STC to be generated for any such equipment change or replacement, according to Bohaboj. Even if the equipment involved is completely or nearly identical in installations in different aircraft types, differences may exist in the interfaces between the newly added equipment and different aircraft types’ power, control and cabin environmental systems, she says.

A typical example would be adding a cabin air-ionization filtering system, Sepe says. Small differences in installation requirements are involved in different aircraft types – and aircraft types with larger cabins (and thus greater cabin air volume) need more units for the equipment to work effectively than aircraft with smaller cabins. So the air-ionization installations in larger-cabin aircraft draw more power than in smaller aircraft.

To continue reading this article in the AvBuyer August 2023 digital edition, including the two different types of STC, click the button below…