Navigation and GPS receivers

This category covers the boxes that tell the aircraft where it is: satellite navigation receivers, inertial reference and navigation systems, and the ground-based radio receivers that still sit behind them. The computer that plans the route is under flight management systems, the antennas are their own guide, and the surveillance transponder that reports your position to somebody else is under transponders. The useful question here is not which constellations a receiver tracks. It is which operations the installed system is approved for.

Approval is the specification

A technical standard order sets the minimum performance standard for an article, and a TSO authorisation is the design and production approval issued to a manufacturer that meets it.¹ The authorisation covers the article, and the FAA is explicit that it is not an approval to install and use the article on an aircraft.² So a receiver that carries an impressive TSO is still an unapproved installation until somebody holds the installation approval for your make, model and series, which for a major change by anyone other than the type certificate holder is a supplemental type certificate.⁴ Ask for both, and ask which aircraft the installation approval already lists.

What the augmentation buys you

Satellite navigation in United States airspace is augmented. The FAA describes the Wide Area Augmentation System as a navigation system developed for civil aviation that provides service for all classes of aircraft in all phases of flight, including vertically guided landing approaches in instrument meteorological conditions at qualified locations.³ That is the practical difference between receivers: whether the installed system supports the approach types your operation needs at the airports you actually use. Ask the supplier to name the approach capability in the terms your operations specifications use, and ask what the flight manual supplement will say after installation, because that document is what your crews will fly to.

The integration is most of the invoice

A receiver rarely arrives alone. Ask what has to change around it: annunciators, switching, the autopilot interface, the display, the antenna and its cabling. Ask whether the existing antenna is suitable or whether the installation drives a structural change. Ask what the aircraft downtime is and what a comparable installation actually took, not what the estimate says. Ask who supplies the navigation database and what it costs per year, because a receiver's ongoing cost lives there.

Where the record can be checked

Ask for the TSO and STC numbers and confirm them in the FAA's published design approvals before the deposit.² The register proves the approval and its coverage. It does not prove that the shop quoting the work has done this installation on your model, and it does not tell you what the supplier's support looks like once the aircraft is back in service.

Questions that sort suppliers

Ask which approach capabilities the installed configuration supports on your aircraft. Ask for the flight manual supplement from a previous installation of the same configuration. Ask what the installation kit includes and what it deliberately does not. Ask what happens to the price if the aircraft needs an unplanned structural provision for the antenna.