outside the inlet. They also regulate the amount and
and offset errors related to Mach speeds. The computer
quality of air going to the engine. Electrohydraulic
calculates the specified slope and intercept errors as
actuators, which respond to fixed schedules in the AICS
functions of the indicated pressure ratio (Pti/P) and of the
programmers, position the ramps.
indicated angle of attack (ai).
An electrical total pressure (Pt) input from the right
AICS programmer goes to the ADC backup channel as
airspeed indications for wing sweep.
CAUTION
AUTOMATIC ALTITUDE SYSTEM
Be sure to disable the pitot-static heater
before working on this system. You may be
In the past, the air traffic control system radar
seriously burned by touching the probes.
presented azimuth and distance information to the
controller on a horizontal radarscopes. Aircraft
identification was primarily by voice radio, the use of
TOTAL
TEMPERATURE
PROBE.--Total
position reports over definite fixes, making identifying
temperature (Tt) is the temperature of ambient air plus
turns of the aircraft to headings requested by the
the temperature increase created by the motion of the
controller, or by a beacon identification signal. Altitude
aircraft. Total temperature is sensed by a probe. This
information was given over the voice radio. After this
probe includes a platinum resistance element inside an
information-gathering process, the information was
aerodynamic housing placed in the airstream. The
recorded on a flight strip by the controller and updated as
resistive element, whose resistance varies with
required. When the aircraft moved into another
temperature, acts as the variable portion of a bridge
controller's area, the handoff of the aircraft and the
circuit.
associated information was basically a manual process.
The total temperature probe provides the ADC with
Although the system was adequate, it became
accurate outside air temperature information. The raw
cumbersome during heavy traffic.
information is the indicated total temperature (Tti). The
The increase in air traffic since 1950 has caused
computer smoothes and limits computations on the Tti
serious problems of vertical separation, terrain clearance,
before using the resultant output to calculate true total
and collision avoidance. Because of these problems,
temperature (Tt). Figure 6-19 shows a typical
improved air traffic control techniques were developed.
temperature-sensitive bridge circuit that provides
These techniques included the use of altitude-coded
temperature data to the air data computer.
transponders for automatic altitude and position
reporting.
AIR INLET CONTROL SYSTEM.--The air inlet
Automatic altitude reporting equipment that
control system (AICS) decelerates supersonic air. It also
provides continuous automatic identification of aircraft on
provides even, subsonic airflow to the engine throughout
the ground controller's radarscopes has been developed.
the flight envelope. The AICS is similar to the variable
This equipment cuts out many of the manual steps
inlet duct ramp system mentioned in chapter 5. Three
required in the old air traffic control system. An air data
automatically controlled hinged ramps on the upper side
computer corrects static pressure errors and provides
of the intake vary inlet geometry. The ramps position to
synchro-driven altitude information to the pilot's
decelerate supersonic air by creating a compression field
altimeter. It also provides altitude in digital form to the
aircraft transponder in high-performance aircraft. In low-
performance aircraft, the equipment provides a direct
readout of altitude to the pilot and digital altitude
information to the aircraft transponder. The digital
information then goes to the ground interrogator and
shows on the radarscopes in alphanumeric form.
The automatic altitude system operation is discussed
in the following paragraphs. An interrogation pulse group
goes from the interrogator-transmitter unit through a
directional interrogator antenna assembly. The pulse
group triggers an airborne transponder, causing a
Figure 6-19.-Total temperature circuit.
multiple pulse reply group to be transmitted. The
