Title 14 of the Code of Federal Regulations (14 CFR) part 91, section 91.103 requires you to become familiar with all available information before beginning a flight. In addition to the required checks of weather, fuel, alternate airports, runway lengths, and aircraft performance, there are a number of requirements unique to the use of avionics equipment. Many of these considerations apply specifically to the use of FMS/RNAV under instrument flight rules (IFR). However, a check of these same requirements before operating under visual flight rules (VFR) enhances safety and enforces good habit patterns, which have been proven to greatly enhance aviation safety.
FMS/RNAV Approval for IFR Operations
Only some FMS/RNAV units are approved for IFR navigation, and it is important to make this determination before flying with any particular unit. Sometimes, this limitation is based on the installation (i.e., method of installation, qualifications of installer), aircraft approval, availability of approved maintenance, and geographic location. No hand-held GPS unit is approved for IFR navigation, and many panel-mounted units are restricted to VFR use only.
Even when an FMS is approved for IFR, the installation of the system in that specific aircraft must also be approved. Even if you have an IFR-approved FMS unit, you may not use it for IFR navigation unless the installation is approved as well. This approval process usually requires a test flight to ensure that there are no interfering inputs, signals or static emanating from the aircraft in flight. RNAV units that do not meet all of these requirements may still be used as situation enhancing navigation resources when operating under instrument flight rules.
The first place to check when determining IFR certification for an FMS is the Pilot’s Operating Handbook (POH) or Aircraft Flight Manual (AFM). For every aircraft with an IFR approved FMS/RNAV unit, the AFM explicitly states that the unit has been approved for IFR navigation and what IFR operations are specifically authorized for that installation.