ILS — Instrument Landing System

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.

Transponders

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.

GPS — WAAS

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.

GPS — Global Positioning System

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 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.