Definition
An FAA Technical Standard Order that specifies the minimum performance standards for stand-alone GPS/WAAS navigation equipment installed in aircraft. Equipment certified under TSO-C146 uses GPS signals augmented by the Wide Area Augmentation System (WAAS) to provide more accurate, reliable position information than basic GPS alone, and supports approach operations down to LPV and LNAV/VNAV minima. For IFR alternate planning, an aircraft equipped with TSO-C146 navigation equipment may use that equipment to satisfy the alternate airport navigation requirement under specific conditions described in the AIM.
Plain English
A set of FAA rules that say what a piece of GPS equipment must be able to do before it can be installed in an aircraft. Equipment that meets TSO-C146 is the more capable kind of GPS — it uses extra signals that make it accurate enough to fly precision-style approaches.
Context Anchor
Seen in IFR equipment approval and alternate-airport planning discussions, especially when deciding what GPS-based procedures your aircraft may legally use.
Derivation
TSO stands for Technical Standard Order — an FAA document that sets the minimum standard a piece of equipment must meet. The 'C146' is just the catalog number identifying this particular standard. Knowing it's a standard, not a piece of hardware, helps: 'TSO-C146' describes what the equipment can do, not a specific brand or model.
Why Pilots Care
Confirms whether the aircraft GPS can be used to satisfy regulatory requirements for filing and flying to an alternate airport under IFR.
Intuition Check
Do not treat TSO-C146 as the name of an approach or as a blanket permission to do anything with GPS. It is an equipment approval standard; the installed unit, aircraft approval, database, and current rules still determine what you may use.
Example Sentence 1
Because the aircraft's GPS is certified to TSO-C146, the pilot was able to plan an IFR alternate using a GPS-based approach.
Example Sentence 2
Check the equipment list to verify TSO-C146 compliance before relying on GPS for alternate airport planning.