Plan a VFR flight around sunrise and sunset

Updated

Daylight is the one limit of a VFR flight that moves every day. A route that is easy in June can end in the dark in November, and a flight that takes off in light can land after sunset because the leg took longer than you thought. The check takes two minutes at the planning table and it saves a lot of trouble. This guide shows what to look at and how to work back from the light you have.

Sunrise, sunset and twilight

The sun is up between sunrise and sunset. Sunrise is when the upper edge of the sun appears above the horizon, and sunset is when it disappears.

After sunset it does not become dark at once. Civil twilight is the period between sunset and the moment the centre of the sun is 6° below the horizon. There is still light to see the ground and the horizon, and it ends quickly. The same period happens before sunrise, as civil dawn. Night is the rest: the time between the end of evening civil twilight and the start of morning civil twilight.

What a VFR pilot may do in twilight and at night depends on the licence, the ratings and the aircraft, and it differs between countries. AirPlotter does not decide that for you. It tells you which light applies at take-off and at landing, and it is on the careful side: it warns when take-off or landing falls outside the time between sunrise and sunset, which is stricter than the definition of night. Check the rules that apply to you.

Check both ends of the flight

The place where you take off and the place where you land do not have the same sunset. The sun sets earlier in the east than in the west, so a flight to the east lands where the light ends sooner than where you left. Look at the sunset of your destination, at the time you land there, and not at the one of your departure.

The nav log in the planner has a daylight card for this. It lists civil dawn, sunrise, sunset and civil dusk for the departure and for the destination, in UTC and in local time, and it adds a line for the take-off and a line for the landing. Each line says whether it is daylight, and shows a warning when it is not. The local time is the Spanish mainland or the Canary Islands, according to where the place is.

Work back from the sunset

Start from the time you want to land, and not from the time you want to leave.

  1. Find the sunset at the destination. Read it in the daylight card, in local time.
  2. Choose a margin. Land with some time before the sunset, so that a late departure, a delay on the way or a slow approach does not put you in twilight. Choose a margin you are comfortable with, such as 30 minutes; the right one depends on the flight.
  3. Subtract the flight time. The time en route is in the nav log. Take the landing time you chose and subtract it, and you have the latest take-off time. Subtract the time for the start-up, taxi and the departure checks to know when you need to be at the aircraft.
  4. Set that time as the take-off time in the plan. You can set it in Zulu or local time. The nav log recalculates the winds, the times over each point and the daylight lines for it.

For example, if the sunset at your destination is at 18:40 local time, you want to land by 18:10 and the flight takes 1 hour and 10 minutes, the latest take-off time is 17:00. If the plan gives a landing at 18:25, the daylight card shows it, and you know that you have to take off earlier or change something.

If the landing falls too late

When the card warns about the landing, the options are the same ones you would think of in the air, and it is better to choose them on the ground:

  • Take off earlier. It is the cheapest change, and the nav log shows the new times at once.
  • Shorten the flight. A more direct route, a closer destination or a different altitude with less headwind saves minutes. Look at the ground speed of each leg before you change the route.
  • Change the destination to a closer aerodrome, or to one you may use after sunset.
  • Split the flight over two days, or add a stop.

If you plan to land in twilight or at night and your rules allow it, plan the fuel for it. The planner recommends a final reserve of 45 minutes when the landing is at night, against 30 by day, and it shows the advice under the field.

Check it again on the day

Sunset moves by up to a couple of minutes each day, and the flight time moves with the wind. When the flight is near the limit, open the plan on the day, with the real departure time and the winds of that time, and read the daylight card again before you leave.

For the whole process in order, read the guide to planning a VFR flight in Spain. The guide to VFR fuel planning explains the reserve.