Alternate Aerodrome An aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to or to land at the aerodrome of intended landing. Alternate aerodromes include the following : a) Take-off alternate : an alternate aerodrome at which an aircraft can land should this become necessary shortly after take-off and it is not possible to use the aerodrome of departure; b) En-route alternate : an aerodrome at which an aircraft would be able to land after experiencing an abnormal or emergency condition while en route; c) Destination alternate : an alternate aerodrome to which an aircraft may proceed should it become impossible or inadvisable to land at the aerodrome of intended landing. Alternative Trajectory A trajectory which is calculated based on constraints which do not currently apply to the flight. Altimetry-Aiding The process of using altitude data to simulate a GNSS satellite directly over the receiver antenna (i.e., it reduces, by one, the number of satellites required for a given function). Barometric altimetry (calibrated pressure) is most likely to be used in civil aircraft because few, if any, have high range radio (radar) altimeters installed. Altitude The vertical distance of an object measured from mean sea level. Altitude Reconstruction A SASS-C reconstruction process which assigns an expected height to each plot or an invalid height (16FL). Invalid height is assigned if altitude reconstruction is not possible or there is no reliable height information for altitude reconstruction. American Standard Code for Information Interchange/Exchange A 7-bit coded character set; includes alphanumeric, control and graphic characters. Amplitude Modulation A modulation technique where the amplitude of the carrier signal is changed by the amplitude of the information signal. Analogue In radar terms, a signal which has not been converted into digitally encoded values, usually quantified into discrete time periods. Analogue signals are to be found at antenna and receiver level in radar systems. Analogue Data Data in the form of continuously variable physical quantities. Analogue-to Digital Converter 1- A device for the conversion of analogue signals into digital values. Usually operates by sampling the analogue signal at regular time intervals and converting the measured value of the analogue sample to a digitally encoded number.
2- Electronic circuit, which translates analogue signals to digital signals. Analysis A phase of activity which concentrates on trying to understand a situation. Analytical Simulation A particular part-task training based on simulations. It allows to practice in restricted or in real time a part of the skills necessary for the operational task in a realistic environment (PTT or simulator). Angel See Flying Angel

Antenna (General)
In the case of Radar, an electromechanical device for the concentrating of radio frequency energy into a beam of known and predictable direction. An antenna can be used for the concentrating of energy transmitted from or received at the antenna. Typically the beam shape in either to transmit or receive directions shall be very similar (assuming the same or similar transmitted and received frequencies and beam polarisation).The concentration of radio frequency energy may occur in both the azimuth and elevation planes. Normally, but not always, an air traffic control radar antenna is mounted upon a rotating platform such that it can scan a volumetric airspace through 360 deg of azimuth. However, static electronically scanned radar antennas also exist.