How GPS is Different from ADF & VOR in Air Navigation
The principal aim of air navigation is for successfully piloting the airplane without getting lost, breaking aircraft laws or endangering the safety of the passenger. We know it’s really impossible to determine the position of an aircraft at such a high speed and depends on their amount of fuel for their safety. So it’s important for the pilot to know the exact location of the aircraft time by time. Aircrafts are generally navigated under the Visual Flight Rules (VFR) and the Instrument Flight Rules (IFR). In case of IFR, the pilots are permitted to navigate with the help of instruments and other radio navigation devices. Where as in case of VFR pilot moves forward by using direction, speed, time and distance of travel along with visual observation.
Prior to the advent of Global Positioning System (GPS) the two common methods of navigation that pilots frequently used are the Automatic Direction Finder (ADF) and the VHF Omni-directional Range (VOR). ADF is based on non-directional beacons (NDBs) on the ground. These are colored dots depicted on the aeronautical charts and a rectangular magenta box near the symbol represents the name of the station. The relation of aircraft and the station is known as the bearing to the station and that can be calculated on the basis of Relative Bearing (RB) or the reading of ADF and Magnetic Heading (MH). Pilots use these bearings and draw a line on the map to calculate the distance of the bearing to the beacon. Then s/he draws two other lines by taking another beacon that shows the position of the aircraft at the intersection point. Here the pilot uses he ADF navigation unit that points to the station.
However, VOR is a little more developed than ADF in which stations or the beacons transmits signals of two different wave length and these are later calculated to determine the distance of the receiver from the station by relating to the true north. Even most of the VOR station use distance-measuring equipment that enables the receiver to calculate its exact distance from the station. Finally aircraft can be supervised by using radar or the air traffic controller can send information to maintain its position.
Global Positioning System or GPS on the other hand provide position accuracy by the help of 24 earth-orbiting satellites. The position data is updated time by time that is the key point as far as accuracy is concerned. Satellites are positioned in such a way that every GPS unit can locate at least 4 satellites (5 in case of air navigation) to determine its own position. The GPS unit catches the signals of different satellites and measures the time between the transmission and reception of signal. By following the method of triangulation with respect to different satellites the GPS receiver determines its own location. GPS unit calculates latitude, longitude and also altitude. Hence, GPS is now the latest technological innovation used of air navigation and manufacturer now provides units that provide data of all commercial airport including runway length, direction and location. One can update the database at any point of time by using his/her PC.