The process of planning and directing the progress of an aircraft between selected geographic points or over a selected route. The primary tasks are planning the flight, guiding it along the desired route, conforming to special procedures such as noise abatement, and maximizing fuel efficiency.
Flight planning, prior to departure, is for the purpose of developing an operating plan for the conduct of the flight. The operational phase of aviation commences during the cockpit preflight and continues through taxi-out, takeoff, climb, cruise, descent, landing, and taxi-in until the aircraft is parked and the engines are shut down.
The simplest form of aviation is pilotage, in which the pilot directs the aircraft by visual reference to objects on the round. More complex methods rely upon navigational aids external to the aircraft or upon self-maintained and dependent systems.
Like its maritime counterpart, aviation uses the dimension of latitude and longitude, but embraces two additional dimensions the third dimension. Navigation in the vertical plane is introduced when the aircraft is made to climb or descend to reach the proper altitudes at the appropriate points along the route of flight. Time, the fourth dimension, becomes a factor whenever it is necessary to observe time constraints which have been imposed upon a flight, or whenever the progress of a flight is modified so as to arrive at the destination or over a navigational fix at a previously specified time.
Dead reckoning (DR) is at the root of virtually all aviation processes. As a minimum, dead reckoning requires an airspeed indicator, outside-air-temperature gauge, altimeter, clock, compass heading from a point of departure for a specified time and arrive at a dead reckoning position. Dead reckoning is periodically validated by position information obtained from a source external to the aircraft, such as a ground sighting, radio bearing, or celestial observation.
Two broad categorizations of ATC (air-traffic control) procedures are terminal and en route. Terminal operations pertain to departures and arrivals at airports. En route procedures cover that portion of the flight between the departure and arrival terminals.
The purpose of the departure procedures is to issue IFR route clearances, takeoff runway mid taxi instructions, altitude assignments, and climb-out routing. Basic arrival procedures are to accept flights into the terminal control area, expedite airport acceptance furnish landing instructions and information, feed aircraft into the landing pattern, issue approach and landing clearness, and direct landing traffic to parking areas. Severe weather advisories and warnings. including wind shear warnings, are also issued to pilots.
En route procedures facilitate use of the established airway system or pilot-requested director routes between one terminal and another. En route procedures consist of granting of route clearance changes to the pilot monitoring the progress of the flight, and periodically transferring control to the next en route or terminal jurisdiction as the flight advances; instructing the pilot to climb, descend or maneuver laterally to avoid other aircraft; and assisting the pilot in avoiding hazardous weather. Inter-aircraft separations are monitored by using ATC surveillance radars.
Flight service stations
As an adjunct to the ATC system, the flight service stations offer complete preflight planning services. These include pilot weather briefings, ATC and navigation facility status reports, and pilot flight-plain filing services. These facilities also provide en route flight advisory service (EFAS) by VHF radio on significant weather phenomena to help airborne pilots avoid areas of severe or hazardous Weather. Radio-direction findings (RDF) equipment is available to assist lost pilots at many facilities.
A program is under way to automate the systems at the flight service stations. The automated services are to provide the flight service station specialist with weather briefings tailored to the pilot's desired route of flight. The pilot will also be able to receive a weather briefing directly from a voice generation unit driven by the computer. The pilot will have access to this system by using a Touch -Tone phone or a private computer terminal to enter the route request for a weather briefing tailored to the desired route of flight. Consolidation of the flight service function into 61 highly automated facilities started in 1983.
Automation functions provided by the ATC facilities in the order that a pilot would encounter them in a typical approach to land at a major airport.
The ATC system controls the aircraft's movements both on the ground and during flight, and provides a means of allocating available runways and air space between user aircraft. Equipment includes radios, radars, light signals, displays, and other types of electronic instrumentation. The airport control tower directs air traffic in the vicinity of the airport and on the runways and taxiways. Voice communication, navigational aid, weather information, and other services are also provided by the ATC operators to the crew flying the aircraft.
The process of directing a watercraft to a destination in a safe and expeditious manner. From a known present position, a course is determined which avoids dangers and on this course estimates are made of time schedules. The task is to periodically affect en route checks and to make required adjustments.
The method used will depend on the type of vessel and on its role or mission. The devices available and from a simple compass to a host of sophisticated electronic systems. In all cases, the navigator must plan and prepare by setting instruments in order and by checking for predictable current and tidal effects and hazards to navigation en route. This preparation includes having the latest charts and reviewing pertinent sections of sailing directions, light lists, and tide and current tables.
The prudent navigator of a ship planning to cross an ocean will consider the particular requirements of each segment of the voyage. A voyage may be broken up into the following six phases: preparatory, departure, confluence area after departure, high seas, confluence near destination, and terminal.
The methods used to fulfill the requirements of these phases come after one of the following broad categories of navigation: dead reckoning, piloting, celestial navigation, and electronic navigation. The first three categories have become somewhat standardized: the fourth
consideration is being given to phasing out some of the older systems.
An early and still widely used system is the radio direction finder--radio beacon combination which has wide coverage along the coastline and waterways all over the world. Radar is used almost universally. Other widely used are loran A, loran C, Console, Decca, and Omega. There has been a gradual phase-out of loran A and an increased implementation of loran C. Two systems are relatively new on the scene, Omega and the Navy Navigation Satellite System (Transit).
Omega is a very low-frequency hyperbolic system that uses phase comparison measurements from at least three ground transmitters to arrive the position. The propagation of radio waves in the very low-frequency band is characterized by good signal strength and excellent phase stability. Signals are easily received thousands of kilometers from a transmitter. For this reason, only eight transmitters are required for global coverage.
The Navy Navigation Satellite System (Transit), used on a global basis by both military and nonmilitary vessels, consists of satellites in polar orbit plus tracking stations, injection stations and a computing center. The tracking stations follow each pass of every satellite and precisely measure the Doppler shift in the frequency which the satellite transmits. The tracking data are transmitted to the Navy Computing Center where the data is used as the basis for computation of predicted satellite orbital information. The predicted orbital information is transmitted to satellite by the injection stations and is normally updated twice each day. The receiving equipment on the ship, including a computer, receives the signals transmitted by the satellite, measures the Doppler shift, decodes the satellite message, and optimizes the data for position-fixing computation. The passes of the satellites are periodic (every hour), but the computer can be programmed for dead-reckoning position between satellite fixes category, on the other hand, has been under constant and innovative development.
This method of navigation is used when the ship is close to land and involves the use of landmarks and sea marks for frequent determination of position. Such marks may be observed by visual, radio, or sound techniques. Visual piloting consists of sighting by instruments identifiable landmarks, lighthouses, lightships, and buoys. The radio systems most widely used in this piloting sequence are the radio direction finder, which receives signals from shore based marine radio beacons, and radio radar which, besides giving a chart-like pictorial display, can provide bearings and distances for position fixing. The acoustical approach utilizes ultrasonic depth finders. These instruments provide depth measurements which may be compared with those on the chart. Such comparisons can be used to confirm positions or can be used as forewarnings of possible stranding. A development in the area of acoustical devices is the maritime anti-stranding sonar (MASS). The MASS consists of a small shipboard sonar system that sounds an alarm in the presence of bottom conditions and obstacles below the surface that are potentially dangerous to a ship's passage. It is particularly suited to vessels of deep draft or to vessels navigating where bottom conditions are changeable. It could also be of great value to vessels poorly charted areas or in narrow channels.