From the AIM1-1-18 c1) C145 - "Airborne Navigation Sensors Using the GPS Augmented by the Wide Area Augmentation System" C146 - "Stand-Alone Airborne Navigation Equipment Using the Global Positioning System Augmented by the Wide Area Augmentation System"

It appears like C145 refers to only a sensor and C146 refers to a stand alone system. What does this actually mean? How are they different in the airplane? The two different titles seem like they are saying the same thing in a different way.


2 Answers 2


Let's start by clarifying terms. GPS is a positioning system. It provides position, velocity, and time (PVT) data. Navigation involves getting from point A to point B along a defined path. PVT is just one part of that process.

Most large Aircraft have an FMS, which is comprised of many components. Most support multiple PVT sensor inputs; GPS, IRS, radio-navigation (DME/DME, VOR/DME, VOR/VOR). For example, Collins Aerospace produces a Multi-Mode Receiver (MMR), essentially an ILS receiver and a GPS sensor in one box. It also has a precision approach navigator (PAN) function that provide a GPS/LAAS (ILS Look-alike) capability. The GPS sensor is a stand-alone sensor that complies with TSO-C145. It provides PVT data to the FMS and to the ADS-B systems.

General aviation aircraft typically have a stand-alone navigator or integrated flight deck. The latter just packages most of the avionics behind a single user interface in one or more displays. The key difference here is that the navigation functions (the nav database, path definition, path steering, and controls) are all packaged as a bundle. These are then certificated as a GPS Navigator under TSO-146. A common example would be the Garmin GTN series.


I believe that the difference , for aircraft position determination, is that TSO-C145 applies to a GPS/WAAS unit that is a component integrated into a multi-sensor navigation system. For example, an FMS (Flight Management System) that provides navigation using DME/DME/IRU [inertial reference unit]/VOR/DME and a GPS/WAAS. The system selects the navigation sensor(s) providing the most accurate position at any given point based on pre-defined system criteria. (refer to the Aircraft Flight Manual- AFM).

Here is a link to TSO-C145e. Also, below is paragraph 3.d. Functionality from TSO-C145e:

This TSO’s standards apply to equipment intended to provide position, velocity, time information for a navigation management unit application that outputs deviation commands keyed to a desired flight path, or a non-navigation application such as automatic dependent surveillance-broadcast (ADS-B) or terrain awareness and warning system (TAWS). In navigation applications, pilots or autopilots will use the deviations output by the navigation management unit to guide the aircraft. In non-navigation applications, the position, velocity, time outputs will provide the necessary input for the end-use equipment. These TSO standards do not address integration issues with other avionics.

(emphasis is mine)

Then, TSO-C146e applies to a "stand-alone" navigation system using only GPS/WAAS (not part of a multi-sensor navigation system).

Here is a link to TSO-C146e. Also, below is paragraph 3.d. Functionality from TSO-C146e:

This TSO’s standards apply to equipment intended to accept a desired flight path and provide deviation commands keyed to that path. Pilots and autopilots will use these deviations to guide the aircraft. Except for automatic dependent surveillance with Class Gamma, these TSO standards do not address integration issues with other avionics.


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