Maps & Airport/Facility Directories
Pilots use maps or charts to help them navigate while they fly. These maps show all the features of the airspace through which the pilot will fly.

Sectional charts, or maps, are used primarily for flight in good weather under visual flight rules (VFR), in which the pilot can navigate using references on the ground. Sectionals show all the surface features of the land, waterways, coastlines, landmarks, and features of airspace and airports. New sectionals for VFR flight are published every six months.

Other maps are used when flights are conducted under instrument flight rules (IFR) in foul weather with poor visibility. Since these IFR charts are used when pilots cannot see the ground, they provide relatively little data about the landscape, but they do provide the details needed for IFR flight. New IFR charts are published every 56 days.

Pilots also need information about the different airports and air traffic control (ATC) facilities with which they'll work. Much of this information is published in the Airport/Facility Directory (A/FD). A/FDs are updated every 56 days.

Magnetic Compass

All forms of aeronautical navigation can be traced back to the magnetic compass. To this very day, virtually everything that flies, from a Piper Cub to a Boeing 747, has a simple magnetic compass mounted to the windshield or instrument panel. Why? Because it can be used just about anywhere in the world, and it's the most reliable thing in the aircraft, since it uses no power or advanced technology.

As a result, every runway is numbered based upon its magnetic or compass orientation; every heading assigned by air traffic control (ATC) is given based upon magnetic course; and every airway, jetway, or other predefined route segment is assigned a compass course.

GPS — Global Positioning System

GPS is the future of all aerial navigation in the United States. This widely acclaimed space-based navigational technology was developed and is now operated by the U.S. Air Force. In the future, it will replace virtually all of the old land-based navigational technologies, giving pilots a more accurate, reliable, trustworthy, and lower-cost navigation system while saving taxpayers millions of dollars in annual costs. It's now used by millions of people in various walks of life.

Today, many VFR (fair weather) pilots use handheld GPS navigational units with color or black and white moving map displays. These handheld GPS receivers cost anywhere from $500 to $1,800 and can guide pilots safely through their flights in visual flight rules (VFR) conditions. An updated "Nav Database" with information about airports and airspace can be loaded into these units every 28 days, although most handheld units are only updated by their owners once each year.

Pilots wishing to use GPS to navigate in instrument (IFR) conditions like rain, snow, heavy haze, or low clouds, must use special IFR GPS receivers that are approved by the Federal Aviation Administration and are capable of recalling FAA-designed instrument flight procedures.

These IFR-approved GPS units must be permanently installed in the aircraft and must be capable of self-monitoring their own health or integrity, as well as the integrity of the GPS satellite signals.

The use of GPS for IFR flights requires that a current "Nav Database" of information about airports, airspace, and instrument procedures be loaded into these units every 28 days.

VOR

The VHF omnidirectional range (VOR) navigation system has been in widespread use in the United States since the 1950s. However, it is being replaced by GPS.

It's a relatively simple but important system whereby thousands of land-based radio transmitters located throughout the United States and world broadcast special signals to any aircraft within receiving range.

Pilots tune their receivers to a particular VOR station, then the VOR receiver in the aircraft interprets the VOR signal and displays the aircraft's position relative to that individual station.

The aircraft's position is displayed as a function of its magnetic bearing "to" or "from" the VOR station. Pilots can then track toward or away from the station while monitoring their course along that individual VOR radial.

VOR stations are a reference point for the U.S. Airway and Jetway system. These "highways in the sky" are designed primarily by forming routes between different VOR ground stations.

So, when you see the white contrail of a high-flying jetliner make an unexplained turn in the sky and head in a slightly different direction, it's because the jetway, or jet route, that the aircraft is flying on just overflew a VOR, hence the jetway now bends to point to the next VOR station along that route. The replacement of VORs, along with upgrades to the air traffic control (ATC) infrastructure, will one day allow all aircraft to proceed more directly from their points of departure to their destinations.

DME

Distance measuring equipment (DME) does what its name implies: It allows pilots to measure their distance from a VOR station or other navigational aid. DMEs typically display the distance, ground speed, and time to reach the VOR station or navigational aid.

NDB & ADF

Non-directional radio beacons (NDBs) are simple AM radio transmitters that were first deployed in the 1920s and '30s along major airmail routes. These land-based NDB stations broadcast a simple omni-directional navigational signal throughout the sky.

Aircraft carrying simple radio receivers called automatic direction finders (ADFs) tune to these NDB signals. The ADF receiver swings a pointer on the instrument panel that literally points directly to the location of the NDB radio station.

It's a simple and primitive system that's harder to use than most think, and just like the AM radio broadcasts that you listen to, it is subjected to interference from lightning storms.

Data Terminals

Some aircraft are equipped with small data terminals that allow them to exchange text messages with air traffic control (ATC) or their company dispatchers. These terminals also can display weather data in standardized text formats. Some have graphical displays. Most are part of larger flight management systems (FMS).

GPS — WAAS

The Wide Area Augmentation System (WAAS) is a special system that supplements the space-based satellite signals of the primary GPS constellation. WAAS improves the accuracy of GPS for specially equipped aircraft to a few feet, versus tens of feet, allowing the use of GPS for precision approaches all the way down to a runway's surface. WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing errors, and satellite orbit errors. It also provides integrity information regarding the health of each GPS satellite.

ILS — Instrument Landing System

The instrument landing system (ILS) is a ground-based system that guides aircraft to safe landings during periods of low visibility or poor weather. It guides the pilot down an imaginary ramp at a shallow 3-degree angle that leads to the touchdown zone of the runway surface.

ILS works by broadcasting a narrow beam of encoded radio energy that's picked up by a special radio receiver in the aircraft. A cockpit display then shows the pilot his position and displacement relative to the guidance beam (left, right, above, below). The pilot follows this beam toward the runway until "breaking out" of the clouds to complete the landing visually. Bright lights help provide visual guidance to touchdown.

Instrument Approach Procedures

These are the special step-by-step procedures that pilots must follow to safely arrive at or depart from an airport or heliport in low visibility conditions. They involve a combination of textual and graphical instructions, and in many cases also involve the coordinated use of radar tracking data from air traffic control (ATC).

There are three basic types of instrument approach procedures: departure procedures, non-precision approach procedures (which generally get a pilot within 500 feet of the runway surface in horizontal visibilities of one mile or greater), and precision approach procedures (which can get a pilot all the way to the runway surface in horizontal visibilities as low as 500 feet).

Pilots use very small 6-by-8-inch maps called instrument approach plates that show only the features of the airspace and navigational aids used by an individual instrument approach procedure. New instrument approach plates are published every 56 days.

Communication Radios

The overwhelming majority of aircraft in the United States are equipped with two-way communications radios. These radios can range from simple battery-powered handhelds to state-of-the-art integrated navigation and communication systems.

Pilots use their radios to communicate with each other and with air traffic control (ATC), whether in flight or on the ground. At the roughly 18,000 airports without control towers (or when the tower is closed), pilots use a pre-assigned UNICOM (universal communications) frequency to communicate with each other and the people at the airport.

Transponders

The Federal Aviation Administration (FAA) uses radar to monitor the position and flow of aircraft in flight. When the radar beam sweeps across an aircraft, some of that radio energy is reflected back to the radar installation. But the reflection is often relatively weak and contains no altitude information.

To help improve the "visibility" of aircraft as radar targets, aircraft are equipped with little boxes called transponders. The transponder detects the radar sweep, and in response, generates its own very powerful return pulse. This 200-watt pulse makes the aircraft much easier to see on radar.

Aircraft operating near major cities, at high altitudes, and in some types of airspace, are required to use altitude encoding transponders. The transponder is connected to a little electronic device on board the aircraft that measures the aircraft's altitude. The transponder encodes the altitude data into the return pulse that it broadcasts to air traffic control. ATC uses the altitude data to help separate different aircraft from each other. Other airplanes with traffic alert and collision avoidance systems (TCAS) can see and use the altitude data. These transponders must be checked for accuracy every 24 months.

When air traffic controllers want to distinguish one airplane from another, they will temporarily assign the pilot a unique four-digit transponder code (some codes are reserved for special purposes).

Once the pilot has set the transponder to the specified code (called "squawking" i.e., squawk 4367), ATC's radar display will then isolate the target aircraft from all the rest. This allows the controller to assign the aircraft's registration number (it's N-number) or flight number to the individual blip on the radar screen.

The information assigned to the radar blip is called a data block. The data block follows the airplane through the ATC system as it's handed from one controller to the next throughout its flight.