AIM Text
Use reasonable restraint in exercising the prerogative of VFR flight, especially in terminal areas. The weather minimums and distances from clouds are minimums. Giving yourself a greater margin in specific instances is just good judgment.
- Approach Area. Conducting a VFR operation in a Class B, Class C, Class D, and Class E surface area when the official visibility is 3 or 4 miles is not prohibited, but good judgment would dictate that you keep out of the approach area.
- Reduced Visibility. It has always been recognized that precipitation reduces forward visibility. Consequently, although again it may be perfectly legal to cancel your IFR flight plan at any time you can proceed VFR, it is good practice, when precipitation is occurring, to continue IFR operation into a terminal area until you are reasonably close to your destination.
- Simulated Instrument Flights. In conducting simulated instrument flights, be sure that the weather is good enough to compensate for the restricted visibility of the safety pilot and your greater concentration on your flight instruments. Give yourself a little greater margin when your flight plan lies in or near a busy airway or close to an airport.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-3-16.
Research Notes
AIM 4-3-16 covers RNAV departure procedures — Area Navigation departure routes that use GPS-derived waypoints rather than ground-based navigation aids.
RNAV SID concept: A Standard Instrument Departure (SID) that's defined by waypoints rather than VOR radials. RNAV SIDs use latitude/longitude fixes that any RNAV-capable aircraft (GPS) can fly. They allow tighter departure paths than VOR-based SIDs.
RNAV requirements: The aircraft must have FAA-approved RNAV equipment (typically WAAS GPS for the most demanding RNAV procedures). The pilot must verify the FMS/GPS database is current (28-day or 56-day cycle).
Pilot procedures:
- Load the SID into the GPS/FMS before departure
- Verify each waypoint matches the chart
- Cross-check track and altitude during the departure
- Brief the SID before taxi: route, altitude, climb gradient, transition points
Common RNAV departure errors:
- Loading the wrong runway transition (multi-runway SIDs)
- Not verifying GPS database currency
- Missing climb gradient requirements
Reference: AC 90-100B (U.S. Terminal and En Route Area Navigation (RNAV) Operations); AIM 5-2-8 (Standard Instrument Departures); AIM 4-3-16.