AI AIRCRAFT INTECEPTION [Main Title]

A radar training film for aircrew, explaining the principles of the AI (aircraft interception) radio equipment, with emphasis on the interpretation of the data presented on the display unit. Effective use is made of animated diagrams and close up photography woven around a lucid narrative. The remainder of the film features a Beaufighter using the AI system to track and attack an enemy aircraft.

Reel one: Film opens with a Beaufighter taking off into heavy cloud. Animated diagram shows aircraft emitting radio waves and the reflections received from an enemy aircraft in the vicinity. Film shows the TX/RX antennae on the wings of the Beaufighter, transmitting intermittently, to allow the reflected pulse to be received during the intervals and displayed on a special receiver comprising two cathode ray tubes (CRT). Having thus detected the enemy, the pilot needs to know the range, azimuth, flight direction and height of the enemy. These parameters are determined by the use of four additional antennae, two on each of the port and starboard wing's upper and lower surfaces. A series of animated diagrams explain the electronic controls and function of the antennae which send a sequence of reflections to the twin CRT display from which the required parameters may be determined.

Each CRT tube has a horizontal time base generated by an oscillating spot of light that is synchronised to the rate of transmission of the pulses from/to the antennae. A reflected pulse appears as a 'blip' on the time base. Clutter, noise from ground or sea reflections, can mask these blips if the (friendly) aircraft is too low, and is minimised by an increase in height. The onset of clutter may be used to determine the aircraft's height. The reflections from the four wing mounted antennae, left/right and up/down are displayed by the two CRT, left/right on the horizontal time base, up/down on the vertical time base, to aid viewing by the navigator. A mechanised rotary switch selects each antenna in turn, and at high rotation speeds, the four traces are combined into two, representing elevation on one CRT, azimuth on the other.

Reel two: Opens with a Beaufighter orientated and flying level towards an enemy aircraft. This is confirmed by the twin CRT displays where the four composite blips (enemy azimuth and elevation) are placed symmetrically around the two time-bases. If the enemy deviates from his flight path, this will be detected by the Beaufighter navigator as he notes either or both blips becoming asymmetric on the time base. The pilot changes his direction as directed by the navigator to restore symmetry to the composite blips. The range is determined from a combination of the Beaufighter's height (altimeter) and the distance to the onset of clutter.

The film now features a Beaufighter conducting a successful attacking on an enemy aircraft. Beaufighter R2078 (RAF) on the ground. Pilot and navigator climb aboard, and take off. Ground defence control contacts the pilot; "bandits SW of you, angels 14, vector 210, is flash weapon fitted?" Pilot confirms and asks navigator has the enemy been detected? Blips appear as navigator and pilot commence attack, the changing disposition of the blips reported to pilot who responds accordingly to follow the enemy. Enemy sighted, pilot adjusts the reflector gunsight, fires guns, enemy falls away and crashes to the ground. Throughout this attacking sequence the film focuses on the twin CRT, showing the movement of the blips in response to the pilot's actions.

35mm