Definition
TSO-C145 is an FAA Technical Standard Order that sets the minimum performance requirements for a GPS navigation sensor that is augmented by a Satellite Based Augmentation System (SBAS), such as WAAS in the United States. A TSO-C145 unit is a sensor only — it provides position data to a separate flight management or navigation computer, rather than being a complete standalone navigator. Equipment approved under TSO-C145 may be used to fly GPS and RNAV (GPS) approaches, including LPV and LNAV/VNAV approaches, when installed and approved for that purpose.
Plain English
It is the FAA standard that a piece of GPS equipment has to meet to be trusted for IFR navigation when it works together with WAAS. Equipment built to this standard is a position sensor that feeds another box, not an all-in-one navigator.
Context Anchor
Seen in instrument flight rules alternate planning and equipment discussions, especially when deciding whether an installed satellite navigation system may be used for approach or alternate requirements.
Derivation
TSO stands for Technical Standard Order — an FAA document setting minimum performance standards for a specific piece of equipment. The 'C145' is just the catalog number identifying this particular standard. Knowing 'TSO' means 'minimum approved spec' is what makes the term useful in practice.
Why Pilots Care
Only equipment meeting this standard can be used for certain GPS-based IFR procedures and alternate requirements without additional restrictions.
Intuition Check
Do not read TSO-C145 as the name of an approach, route, or GPS brand. It is an FAA equipment standard, and the aircraft records or approved flight manual tell you whether your installed equipment meets it.
Example Sentence 1
Because the aircraft is equipped with a TSO-C145 GPS sensor feeding the flight management system, the crew can file an LPV approach as the primary destination procedure.
Example Sentence 2
Equipment certified to TSO-C145 supports LPV approaches with vertical guidance.