Definition
An FAA Technical Standard Order that sets the minimum performance standards for stand-alone GPS/WAAS navigation equipment installed in civil aircraft. Equipment built to TSO-C146A is approved for use as a primary means of navigation in oceanic, domestic en route, terminal, and approach phases of flight, including LNAV, LNAV/VNAV, and LPV approaches.
Plain English
It is the FAA rulebook that says what a WAAS-capable GPS unit must be able to do before it can be installed in an aircraft and used on its own for navigation, including instrument approaches.
Context Anchor
Seen in discussions of WAAS-capable GPS equipment, avionics manuals, aircraft flight manual supplements, and instrument flying requirements for advanced navigation systems.
Derivation
TSO stands for Technical Standard Order, an FAA document that defines minimum performance for a specific piece of equipment. The 'C146A' is just the catalog number identifying this particular standard, with the 'A' indicating the first revision.
Why Pilots Care
Equipment meeting this standard provides the accuracy and integrity needed for safe GPS-based instrument approaches.
Intuition Check
Do not read TSO-C146A as a general promise that every GPS use is allowed. It is an equipment standard; the specific aircraft installation and operating approval still matter.
Example Sentence 1
Before filing for an LPV approach, the pilot confirmed the aircraft's GPS receiver was certified to TSO-C146A.
Example Sentence 2
Before flight the pilot confirmed the navigator met TSO-C146A requirements listed in the aircraft flight manual.