Do you ever wonder how one could simply sit back on an aircraft, takeoff, climb and cruise across the globe to only arrive completely on the other side of the planet! Modern jets use a few main navigation methods including:
- Global Positioning Systems (GPS).
- Inertial Reference Systems (IRS).
- Traditional radio aids e.g. VOR, DME, ADF and ILS.
In modern aircraft Pilots can program or load a company planned flight route into the aircrafts navigational systems which later on the autopilot can fly with a very high precision level. Navigation displays in the aircraft also show pilots weather information, terrain obstacles, other aircraft traffic and waypoints and navigation aids. The system then also generates both time and fuel predictions for pilots to monitor throughout the flight.
Lets take a brief look at these navigation methods:
GPS (Global Positioning system)
This now days is one of the main primary ways of navigating. It utilises the on board GPS receivers via satellite based feedback to attain the aircrafts accurate position in flight. Usually the aircraft has more than one GPS receivers in case one fails but in the vent both failed or GPS data becomes invalid, then we still have the other two methods mentioned below to continue navigation fairly accurately along the planned routing.
IRS (Inertial Reference System)
This is a self contained system in the aircraft that is capable of tracking position using accelerometers and gyroscopes. During pre-flight phases, on the ground, the pilots can input the exact co-ordinates (lateral and longitudinal) into the IRS system for it to initialise the starting point or position. Usually airport charts always annotate each gates co-ordinates for this purpose. The IRS system there after will then detect any applied acceleration across any of its axis and continuously calculate drift from start to compute a new position.
Most aircraft have multiple IRS gyro's which each independently compute a position. The several positions are then plotted to crate a mixed IRS average position for a more bias position value. Multiple IRS systems also mean there is redundancy built in but if the system entirely failed, then we are still capable of navigating using traditional radio beacons mentioned below.
Radio beacons e.g. VOR, NDB's etc. allow the aircraft to automatically or manually tune into the beacon using its designated frequency provided it is within range. The aircraft can utilise these beacon radials and distance information to compute a fairly accurate position. The idea is often to use several beacons and distance feedback to compute a more accurate value based on the triangulation of this data available.
This shows you that in modern aircraft navigation through several waypoints along a route to reach your destination not only has a lot of redundancy built in but can be done very accurately for thousands of miles. The worst case scenario can be to loose all possible navigation systems on board but even then if the aircraft is within ATC radar coverage, pilots can always ask for vectors to safely come back and land. There on the big boys from the hangar also known as engineers can come with their screw drivers and pliers to fix the problem whilst you call it a day and fill the necessary paper work!