Have you ever wondered how pilots can take off, land, and navigate in bad weather? When I was a kid I certainly did. I remember landing at LaGuardia airport in New York when I was young sitting in a window seat and looking out into dense clouds. I was not even able to see the tip of the wing, yet there we were flying at over 200 mph. I remember suddenly out of nowhere the runway appeared. How'd they find it?
Nowadays, aircraft can fly themselves - even land themselves. Aircraft systems have become very integrated over the years and the level of sophistication that engineers have achieved has made air travel much safer, whether or not the weather is bad.
One of the most notable breakthroughs is the implementations of GPS into everyday navigation. Today, many aircraft designers have coupled GPS to autopilot, which means that once it is safe for the pilot to engage the autopilot the autopilot will follow the route entered into the GPS.
GPS has software associated with it that reads from a database of the locations of every navigation aid (or navaid), airport, and uses this information to display (in real time) the aircraft's position. In addition, the GPS software usually has an interface where a pilot can find useful information such as the radio frequencies for other navigation aids, air traffic control, control towers, and ILS localizers.
One crowning achievement in GPS technology is the integration of TCAS, or Traffic Collision Avoidance System, onto the GPS display. TCAS is essentially a short-range RADAR system that displays other aircraft in the area on the GPS map in relation to the position of the aircraft. TCAS will also show the direction of flight of the other aircraft as well as their altitude (also in relation to the aircraft).
But people were flying aircraft long before GPS was invented. In the years preceding GPS, pilots solely flew by instruments. The navigation aids used then are still in use today, and one of the most widely used tools is the VOR radio. VOR stands for Very high frequency Omnidirectional Radio Range. A VOR radio emits radio signals at a unique frequency from the ground 360 degrees around. Aircraft have audio/visual receivers and use these signals, among other things, to verify their position or to use as a waypoint. The radio equipment on an aircraft is equipped to translate these signals and display them onto the VOR display which is nothing more than crosshair needles that move based on the aircraft's position in relation to where the signal is coming from. For example, if the pilot is flying directly towards the radio (or directly away from) the vertical needle will be centered. Since there is a finite number of radio frequencies in the band used for these radios, many frequencies are used more than once. To make sure a pilot has the correct frequency tuned, VOR radios continuously transmit a unique Morse-code signal that the VOR radio receiver on the aircraft can play.
Another navigation tool that pilots use is an NDB, or Non-Directional Beacon. This is another radio transmitter at a known location and the signal sent from it does not include directional information. To find the source of the signal, the second part of NDB navigation is the ADF, or Automatic Direction Finder. The ADF, when tuned to the appropriate NDB frequency, will essentially point to the direction of the NDB.
There are many more tools a pilot can use to fly when they can't see out the window, but described above are the most common and widely used. To be completely honest, pilots spend a great deal of time scanning these instruments even when they can see out the window - so good weather or bad you can be sure that whomever is flying the plane you happen to be on is well-versed using this equipment.