In the early days of aviation, pilots navigated the skies by looking out the window and locating visual landmarks, or by celestial navigation which consisted of finding one’s way by observing the sun, moon, and stars. For example, in the 1920s, US airmail carriers used strategically placed bonfires as their aids, and during the day, they would use oversized concrete arrows that were placed on the ground for guidance.
The former navigational method is called pilotage and serves as one of the first navigation techniques taught to aspiring pilots because it was both easy to grasp and foolproof. As previously mentioned, it required that pilots look out the window to spot landmarks like cities, towers, rivers, lakes, mountains, and more. At night, pilotage is achieved by locating city lights, highways, and airports. However, pilotage is limited to VFR weather conditions when the pilot has the ground in sight.
Alongside pilotage, dead reckoning was also used and consisted of calculating distance and time based on the ground speed of the aircraft. For instance, pilots must calculate the time it should take between checkpoints on the ground if they fly at a specific airspeed. Additionally, there are non-directional beacons which are radio beacons that, when coupled with automatic direction finder (ADF) equipment in aircraft, interpret an NDB signal to provide an indication of where the pilot is in relation to an NDB station.
As GPS navigation has become more commonplace, the aforementioned methods are falling in popularity. Luckily, technology today has made navigating a plane a lot easier, and with so many flight instruments at a pilot’s fingertips, traversing the air is simpler. Aircraft instruments encompass various displays and dials in the cockpit that pilots can use to help them understand where the plane is and what it is doing. This is especially helpful when flying thousands of feet in the air and visibility is not optimal.
Even if pilots could see, the ground is so far away that it is often very difficult to tell how their altitude is changing. This is where aircraft instruments are helpful. Describing one’s position requires that you know exactly where you are within the atmosphere relative to earth’s features. While you may be able to identify more obvious points of interest like the Eiffel Tower in Paris, France, most of the landscape elsewhere is pretty nondescript and hard to make out.
An altimeter is a flight instrument that describes an aircraft’s altitude above sea level (ASL) by measuring the vehicle’s surrounding atmospheric pressure. Meanwhile, an altitude indicator (AI) is a display that shows an artificial image of a horizon and miniature aircraft, intended to resemble the plane being flown positioned relative to the horizon. Essentially, it tells pilots whether the wings are level or tilted to one side which is the “roll” or “bank” of the plane. More than that, it tells pilots whether the nose of the aircraft is pointing above or below the horizon which is the “pitch” of the plane.
In general, pilots must know how to fly a plane without an AI, but it does help during low visibility conditions. Next, an airspeed indicator (ASI) shows the aircraft’s speed relative to the surrounding air, and it functions by measuring the ram-air pressure in the aircraft’s pitot tube relative to the ambient static pressure. Furthermore, a heading indicator, also called a directional gyro or DG, displays the aircraft’s heading in relation to magnetic north when set with a compass. In more advanced aircraft, this instrument is replaced by a horizontal situation indicator (HSI).
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