How do pilots navigate through clouds and at night ?
How do we find our destination without using Google maps to lead us the way?
When in flight school we learn to fly, we start with VFR, Visual Flight Rules. We navigate visually from town to town, using lakes, rivers and roads as reference.
In a later stage, we learn to navigate using Instrumental Flight Rules (IFR). This is based on radio beacons, waypoints and airways, as you can see on the chart. Most often, we use the following radio aids:
- VOR – VHF Omnidirectional Range
A VOR is transmitting signals in a circle around itself. It gives the pilots information where they are in relation to the station. In the animation you can see that the airplane is on radial (bearing) 118, but if it moves further north, it will pass various radials and end up at radial 057.
On a RMI (Radio Magnetic Indicator) the indication is very straight forward as the arrow will indicate the direction of the station. On other indicators such as an HSI (Horizontal Situation Indicator) or CDI (Course Deviation Indicator), you can select a certain radial (course) that you want to fly and it will indicate your deviation from the desired radial.
- DME – Distance Measuring Equipment
Usually combined with a VOR. In this way, we receive not only the direction to the beacon, but also the distance towards it. The distance is calculated from the time difference between the interrogation signal (from the aircraft) to the reply signal from the ground station. (Picture of chart with VOR DME navigation)
- ILS – The Instrument Landing System
The Instrument Landing System consists of a Glide Slope and a Localizer. It is a very accurate landing assistance as it gives us an immediate indication of the desired flight path until the landing, both vertical and horizontal.
If we are too low on the glide slope, the indication on our cockpit instruments will show us we need to fly more up, and if we are too much to the left of the localizer, we will read that we need to fly more to the right.
- GNSS – Global Navigation Satellite System
Modern jet aircraft also use GNSS for area navigation. GPS is a type of GNSS, but also Glonass, Beidou and Galileo. Satellite navigation is also very accurate and as it is satellite based, it does not require any of the ground-based radio beacons. Most commonly, our flight plan route is given in waypoints: GPS locations with 5-letter names and are in the airplane’s database. Because of the use of these waypoints, we don’t need to actively navigate with radials and distances from VORs when we are in cruise.
Using all these different radio aids, pilots can navigate in the clouds or at night without the need to see the ground until the landing.
But up to what moment can we fly without seeing the ground?
The last part of the flight, before the landing, is called the approach. Besides visual approaches, we make ILS approaches and VOR approaches. When we know which approach and which runway is in use, we take the appropriate chart, where all information is given with regards to directions and headings, altitudes and our Minimums.
Minimums, the minimum decent altitude or decision height, is where we need to see the runway (or the runway lights) in order to continue our approach, otherwise we have to make a go around and start the missed approach procedure!
However, using the most advanced ILS system, we may be allowed to make an automatic landing. Which means that the minimums are practically zero, or 50 feet above the ground and we can let the airplane fly all the way up to and including the landing.