STC Tips by Mike Keirnan, Mgr Installations & Certification Before you install, or even quote, an S-TEC system in an aircraft, there are some points to consider that might affect the cost, installation time, available options, and even the validity of the STC for that aircraft. Modifications to the airframe (STC's), that affect aircraft structure, aerodynamics, performance, or CG range, can invalidate the approval for an autopilot. Certain factory options on aircraft may dictate that additional parts from the manufacturer be installed to complete an installation, or may preclude the installation of certain S-TEC options. An aircraft that has had a significant repair in the areas where autopilot components will be installed, may require modifications to installation components, and subsequent DER approval of those modifications. This could impact the cost and downtime for the installation. By studying the notes in the STC Directory of the S-TEC Sales Manual for the aircraft and system under consideration, the impact of these considerations can be better understood. Modifications that need to be considered relative to STC impact include: STOL kits Floats, skis, and tailwheel conversions Wing tip reconfigurations Strakes, turbulators, gap seals, and root fairings Engine modifications (additional HP or turbo-charging) Extended range fuel tanks - both internal and external Cabin modifications (seating changes, door installations, etc.) Also, be sure that any combination of modifications is considered, either as addressed in the S-TEC STC or by consulting S-TEC Flight Engineering. In some cases airframe options may impact the installation of an S-TEC system. Additional brackets, cables, or control hardware could be required from the aircraft manufacturer to complete the installation. For example, some Beechcraft and Cessna twins equipped with factory manual electric trim will require the installation of additional cables. Another example is the alternate trim servo installations for some Cessnas with air conditioning. You should always consider the following factory options as suspect for STC impact: Air Conditioning Club seating Manual electric trim Extended range fuel tanks Autopilots Yaw dampers Damage history is not uncommon when you consider the average age of the general aviation fleet. Review the logs and inspect the airframe for damage repairs in the area where the autopilot components will be installed. Doublers, additional stiffeners, or fasteners installed in a previous repair, may interfere with the autopilot installation. Any modifications required for the installation are mods to the STC and must be documented, tested, and approved. Encountering some of the things discussed here, doesn't mean that an installation can't be made. However, understanding what is required before you begin will enable you to be accurate in your quotation to your customer. Please feel free to request help from Flight Engineering before quoting a price and schedule. Call us anytime you have any doubt about an aircraft or modification - we can help.

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