CONTROLLER-PILOT DATA LINK COMMUNICATION

NAVIAGTION SYSTEM – INS

Navigation across oceans and in areas where few ground-based navigation aids exist is normally achieved byusing an Inertial Navigation System (INS), In use an INS is given the aircraft's start position, it then senses all movements the aircraft makes and continuously updates the position of the aircraft. Normally triplicated systems are used to eliminate the possibility of error and ground based radio aids are used, where available, to update the positional accuracy which has a tendency to drift by a mile or two an hour.

NAVIAGTION SYSTEM – NDB

Non Directional Beacons (NDB) transmit signals (200-1720KHz) in alldirections and are point source navigational aids. Their range is normally around 40 miles. They are generally used is a locator beacon to provide airfields with holding facilities and a non-precision approach. With higher power their range can be around 150Nm when they can act as an en route navigational aid. The use in the en route role is only common in remote areas and areas of low traffic density.

NAVIGATION SYSTEM – LANDING AIDS

The localizer (VHF 108-112MHz, range 25NM) provides guidance in azimuth and the glidepath (UHF 328 335 MHz, range 10NM) provides guidance in elevation.

In use the pilot establishes the aircraft on the final approach track (defined by the localiser) at distance of around 12 Nm and a height of 3000 ft. At this point the aircraft is below the approach slope defined by the Glidepath. When the pilot intercepts the Glidepath descent is started and the localiser and Glidepath are followed down to the pilots approach minima.

The pilot determines the distance from touchdown by fixed distance marker beacons (75MHz) located on the extended centre-line about 3.5NM(outer marker)and 3500ft (middle marker)from the runway threshold. Each beacon radiates a characteristicand easily identifiable signal. These provide fixed points where distance to go can be checked against the aircraft height, thus confirming theaccuracy of the altimeter setting.

CONTROLLER-PILOT DATA LINK COMMUNICATION

CPDLC is communication system which allows pilot and controller to communicate with the help of data link. CPDLC allows controllers to issue common clearance directions, such as flight level assignments and constraints, frequencies, route changes and deviations, speed restrictions, and requests for information. The flight crew can then respond.

The CPDLC application provides air-ground data communication for the ATC service. This includes a set of clearance/information/request message elements which correspond to voice phraseology employed by Air Traffic Control procedures. The controller is provided with the capability to issue

· level assignments

· crossing constraints

· lateral deviations

· route changes and clearances

· speed assignments, radio frequency assignments

· various requests for information.

The pilot is provided with the capability to respond to messages, to request clearances and information, to report information, and to declare an emergency. The pilot is, in addition, provided with the capability to request conditional clearances (downstream).A “free text” capability is also provided to exchange information not conforming to defined formats.

The benefits of flight deck integrated ATC systems include the following:

√Enhanced flight crew situational awareness.

√Shift of workload from controller to pilot. For example, controllers can issue sequence positions and pilots can be left to maintain their sequencing without further controller direction.

√Alleviates miscommunication problems.

√Improved efficiency and system capacity by allowing a reduction of necessity to repeat missed messages or correct errors in read-backs.

√Data-link communication can act as a back-up to traditional radio communication.

√Digital communications are (generally) more reliable than analogue communications.

But these radio communications are inherently vulnerable to error.

§ Resources for radio communications (particularly frequencies) are limited.

§ When there is congestion of air traffic it requires from controller high workload

§ Congestion on ATC frequencies results in communication errors, particularly due to blocked transmissions (which themselves only generate further congestion).

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