Add NVFR navaid alternate

docs/flight-planning/alternaterequirements.md

@@ -8,7 +8,7 @@
 An alternate aerodrome is an aerodrome nominated by the pilot at the flight planning stage which will be used as a divert point should the planned destination become unsuitable for any reason. In the real world, there are many reasons why an alternate may need to be carried. This page simplifies some of the real world rules and highlights the ones which are applicable for VATSIM operations.
 
 ## Alternate due Weather
-When planning a flight, make careful study of your destination's TAF and take note of the cloud, visibility, and wind during the period of 30 minutes either side of your ETA (60 minute window). Compare the forecast values with the alternate minima described below. If a TAF is not available for your arrival window, you must hold an alternate.
+When planning a flight, make careful study of your destination's TAF and take note of the cloud, visibility, and wind during the period of **30 minutes either side of your ETA** (60 minute window). Compare the forecast values with the alternate minima described below. If a TAF is not available for your arrival window, you must hold an alternate.
 
 You must plan an alternate (or carry sufficient holding fuel, see [Fuel Planning](fuelplanning.md)) if:
 
@@ -36,6 +36,9 @@ For helicopters operated under Day VFR to an uncontrolled (Class G) aerodrome, t
 | ----- | ---------- |
 | 1,000ft AGL | 3km |
 
+!!! note
+    An alternate is not required if you are flying under Day VFR and plan to remain within 50nm of the departure aerodrome.
+
 ### IFR Alternate Minima
 The IFR alternate minima is described on any approach chart for that aerodrome. The figures are formatted as cloud height above ground level and visibility in kilometres.
 
@@ -54,12 +57,15 @@ If your destination does not have an instrument approach, you must plan an alter
 
 ## Alterante due Navaids
 ### IFR
-An alternate must be held for IFR flights if due to the aircraft's equipment or the destination aerodrome's navigation aids, a single point of failure in the aircraft or on the ground would cause a loss of approach capability. In principle, this means that your destination has only a single approach type available or your aircraft has only a single piece of equipment which can receive that data, you must carry an alternate.
+An alternate must be held for IFR flights if due to the aircraft's equipment or the destination aerodrome's navigation aids, a single point of failure in the aircraft or on the ground would cause a loss of approach capability. In principle, this means that if your destination has only a single approach type available or your aircraft has only a single piece of equipment which can receive that data, you must carry an alternate.
 
 !!! example
     Flying a B737 (with multiple GPS, VHF NAV, and ADF equipment onboard) to Orange (YORG), which has published RNP approaches but no ground based aids, would require an alternate, as a loss of RAIM or GNSS integrity would result in the aircraft being unable to conduct an approach.  
 
     Flying a C172 (with a single GPS, VHF NAV, and no ADF) to Sydney (YSSY) would *not* require an alternate, as a failure of a single piece of equipment in the aircraft (e.g. the GPS) or on the ground (e.g. the ILS) would not prevent the aircraft from conducting an approach (they could still utilise the RNP or ILS approach, depending on the source of failure).
 
 ### Night VFR
-- GNSS/navaid or alternate within 1hr (double check)
+An alternate, within 1 hour flying time, is required for Night VFR flights unless:
+
+- The aircraft is equipped with GNSS, or
+- The destination is served by a ground-based navaid which the aircraft has equipment to receive