Sights and Sightlines in the Sky

There’s always that friend who claims that they have an expert sense of direction. Luckily, not all pilots need to have an intuitive sense of north and south, to fly an aircraft to its destination. There are a series of protocols and navigational instruments that help the pilot pinpoint the aircraft’s exact destination, and their progress along the flight path.

There are two main visual techniques that pilots are trained on before flying an aircraft. Pilotage is the sole use of visual ground references to navigate the plane. For example, if a pilot was flying over London, they will probably use the O2, tower bridge, the Gherkin, and Buckingham Palace as visual references. Dead reckoning is similar to pilotage; however, the pilot calculates the distance between each visual reference. So, the pilot would use distance, airspeed, and wind calculations to determine how long it takes to fly over the 02 and then Buckingham  Palace. Additionally, flight computers help the pilot with the math and typically the pilot keeps track of the calculations during flight.

While these two techniques are all good and well in prime flying conditions, they are not suitable for days when adverse weather conditions, which can leave the pilot with little to no visibility. Most technically advanced aircraft are fitted with radio navigation aids (NAVAIDS) that help aircraft navigation. The basic concept of NAVAIDS is this: the pilot steers the aircraft more or less in a straight line to a designated point on the ground, an airport for example. From there, they can align with their next point and so on.

VHF Omnidirectional Range (VOR) is the second most commonly used NAVAID system on an aircraft. Again, the pilot uses stationary bases on the ground to help pinpoint the aircraft’s position. Aircraft instruments measure the time between each signal, and the reading is displayed on the horizontal situation indicator inside the cockpit. The reading is usually referenced in terms of the radial position. With the radial reading of the aircraft, the pilot can determine whether they are flying to or away from the stationary base.

As you may have guessed, Global Positioning System (GPS) is the most popular NAVAID used within an aircraft. Instead of using fixed points on the ground, GPS uses the opposite - fixed points in space. 24 U.S Department of Defense satellites are used to triangulate the aircraft’s exact position over Earth. To be accurate, the aircraft must gather data from at least three satellites for 2-D positioning, and 4 satellites for 3-D positioning. The advantage of GPS over VOR or any other NAVAID is that there is little, or no electrical interference and it works pretty much anywhere in the world.

A pilot has various options for how they feel would be best to navigate the aircraft. In some cases, they may not get a choice - during a meteorological event for instance, the radio frequencies are disturbed, therefore the only way to navigate is by pilotage. The growing trend for technically advanced aircraft, however, is GPS or VOR. Pilots must therefore learn to use interpret various cockpit instruments to successfully navigate an aircraft. The FAA states that to be employed as a commercial pilot, a person must be able to use aeronautical charts and a magnetic compass for pilotage and dead reckoning, however as of yet, additional training in GPS systems is optional.


January 18, 2021

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