Navigation is a crucial element of flight operations, allowing pilots and operators to carry out a flight plan to reach an intended destination with ease. While most pilots now rely on highly advanced GPS technology and the Flight Management System (FMS), past operations were much more difficult. This was especially true in the polar regions where magnetic compasses are unreliable. In such instances, pilots would take advantage of what was known as grid navigation.
As stated before, past pilots often had difficulty conducting operations near the poles due to issues with their magnetic compasses. This was due to three reasons, one being the convergence of the meridians of longitude which resulted in constant changes being needed for true heading when the aircraft diverged from true North or South. Additionally, the closer one is to the magnetic poles, the quicker compasses will adjust and become hard to follow. Lastly, areas such as the poles feature much less ground-based navigation aids, making it hard to fly using the surroundings.
True to its name, grid navigation is conducted through the use of grids, those of which are often made to be parallel with a meridian of longitude while being overlaid atop the matching Polar Stereographic projection navigational chart. For an aircraft to follow the grid, they must use a gyro compass that is aligned to the grid, and adjustments may be required every once in a while to take into account the effects of longitude changes and gyro precession. The most popular Meridian to use is the Prime Meridian, and this creates a grid known as the ‘Greenwich Grid.’
While grid navigation proved most useful while near the poles, it still found some use near the mid latitudes for pilots to maintain a constant heading. Generally, these grids did not always follow a particular meridian of longitude, instead being oriented as needed to match the chart projection. Oftentimes, pilots took advantage of the great circle track, that of which would establish grid lines of the same angle so that navigation could be as easy as possible with an aligned gyro compass and optimal weather conditions.
When attempting to fly with reliance on grid navigation, it is important to have an understanding of some common terms. For instance, grid convergence refers to the difference between the true track and grid track. The Datum Meridian is another important meridian to be aware of, and it is where True North is equivalent to Grid North. Variation, or declination, is the angle between True and Magnetic North, and always remembering the difference between each is crucial when flying.
While grid navigation first came about in the 1940s and widely grew in popularity, it began to fall in the 20th century as newer technologies superseded the capabilities of charts. Now, systems like GPS can provide unmatched accuracy that is made possible through the consistent monitoring and communication of satellites. If you find yourself in need of navigation tools or instruments for conducting safe flight operations, we have you covered at Aviation Orbit.
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