Flight management systems

A flight management system is the computer that holds the flight plan, computes the performance and generates the lateral and vertical guidance the autopilot then flies. That sentence is also the category boundary. The autopilot and flight control computers are a separate guide, the receivers that feed the FMS its position are under navigation, and the screens that show its pages are under cockpit displays. A buyer shortlisting FMS suppliers is buying a computer, an approval, an integration and a data subscription, and the four are priced separately by everyone in the market.

The two approvals nobody should conflate

A technical standard order is a minimum performance standard for a specified article, and a TSO authorisation is the FAA's design and production approval to a manufacturer that has shown the article meets it.¹ The FAA states the limit of that approval plainly: holding a TSO authorisation is not approval to install and use the article on an aircraft.² Installation is its own approval, and where the change to type design is major and the installer does not hold the type certificate, that means a supplemental type certificate.³ Ask which TSO the unit holds, then ask which aircraft the installation approval already covers, by make, model and series. Both claims are checkable in the FAA's published design approvals and their searches.⁴

What separates one system from another

Ask which navigation specifications the system is approved to support in your intended operation, and ask for the approval basis rather than a capability list. Ask what interfaces exist to the equipment you already have, item by item: air data, inertial, radio navigation, the autopilot, the displays, the datalink. Ask which functions run in software developed to which design assurance level, and ask for the environmental qualification of the hardware. Both are written against standards produced in RTCA's committees, and a supplier that has done the work answers with document numbers and levels rather than adjectives.⁵ Ask how the system is updated: whether a function change is a software load, a card swap or a new part number, and what each costs in downtime.

The database is the running cost

An FMS without a current navigation database is a paperweight. Ask who supplies the database, what a subscription costs per aircraft per year, what coverage areas are included, and what happens to the price when your fleet grows. Ask how a cycle is loaded, how long it takes per aircraft, and who is allowed to do it. Ask what happens when the supplier ends support for a hardware generation while the aircraft is still flying, because that date is the real end of the purchase.

Where the record can be checked

The FAA publishes its design approvals, so a claimed TSO authorisation, parts manufacturer approval or supplemental type certificate can be confirmed with its holder and coverage.⁴ The register proves the approval exists and what it applies to. It does not prove the unit works well with your autopilot, that the integration has been done before, or that the supplier will still support it in a decade.

Questions that sort suppliers

Ask for the TSO numbers and the STC numbers, then look both up. Ask which installations of this exact configuration are already flying, and on what. Ask for the database subscription price list, in writing. Ask what the last software release fixed and how operators found out.