(12)
 After system has stabilized, close last static cutoff valve. Read and record indication on static system gages.

 NOTE: Accuracy of reading and recording vacuum pressure or
____ equivalent altitude must be | 0.01 inch of mercury or | 20 feet of altitude respectively.
 (13)
 After 1 minute, read and record value indicated on static system gages. Vacuum must not have decreased by more than 0.20 inch of mercury or an equivalent fall of 400 feet in indicated altitude.

 (14)
 Return static systems to ambient pressure (Ref 34-11-00, Maintenance Practices).

 (15)
 Remove test adapters and seals from pitot-static ports.

 EFFECTIVITY

 
 ALL  01 Page 403  Oct 10/7334-11-03
 CENTRAL AIR DATA COMPUTER SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________________
 1.  General_______(See figures 1 and 2.)
 A.  The central air data system provides computed air data to the aircraft flight control, inertial navigation, air traffic control, and air data instrumentation systems. The computer air data outputs are computed functions of altitude, airspeed, mach number, and air temperature. The outputs are derived from dynamic (pitot) pressure, ambient (static) pressure, and total air temperature; all sensed external to the aircraft. On airplanes LH ALL; SN ALL; AF 105-199; AZ 209-299; IB 402 and 405, plus airplanes incorporating SB 34-2016, the central air data computer provides computed air data outputs to the altitude alert system. On XA airplanes incorporating SB 34-2069 or SB 34-2076, the air data computer also provides computed air data outputs to the ground proximity warning system. On AF 151, the air data computer system provides computed air data outputs to the TAT/N1 limit system, the ground proximity warning system and the auto throttle system. On LH 011-030, 051-070, 082-099; AF 121, 122, 152-157, 161, 172-199; AT ALL; IB 406-410; GN ALL; MD ALL; and VM ALL, the air data computer also provides computed air data outputs to the altitude alert, auto throttle, flight recorder, ground proximity warning and TAT/N1 or TAT/EPR limit systems.
 LH 011-030, 051-070, 082-099; AF 115-150, 157, 161, 172-199; AT ALL;
 IB 406-499; GN ALL; MD ALL; AZ 221-299; VM ALL;
 the airdata computer provides computed air data to the gust response
 systems.

 B.  The central air data system consists of two total air temperature sensing probes and two central air data computers. The total air temperature probes are mounted just forward of the captain's and first officer's No. 1 windows. Both central air data computers are mounted in the main equipment center on shelves E1-4 and E1-5 (Fig. 1).
 C.  The system uses single phase, 400-Hz power; 115 volts supplied from essential instrument bus and flight instrument bus No. 2 and 26 volts supplied from flight instrument transformers 3 and 6. Power is also required to supply the anti-icing heater circuits built into the total air temperature probes.
 2.  Total Air Temperature Probes
____________________________
 A.  Each total air temperature probe is a small metal strut mounted external to the aircraft skin. It senses the temperature of airflow passing through cavities within the strut. Air enters an inlet port at the top of the strut and exits through several outlet ports on the side and aft surfaces of the strut.
 EFFECTIVITY

 
 ALL  21 Page 1  Sep 25/9434-12-00
 B.  On airplanes with aspirated probes, the probes have an ejector which when supplied with compressed air permits accurate temperature measurements during ground operation with heater off and gives reduced error with heater on in flight during icing conditions. Compressed air to the probes is supplied from the engine bleed air distribution manifold (36-11-00). To apply air to the probes, one of the following methods must be used: 1) one of the left engines must be running; 2) a high pressure cart to apply air to the airplane and the left isolation valve open (located on the flight engineer's panel); 3) the APU operating and the left isolation valve open.
 C.  A probe contains two temperature sensitive elements each made of precision platinum resistance wire, hermetically sealed within two concentric tubes. Airflow temperature around these sensing elements causes the resistance of the wire to vary as a function of total air temperature.
 D.  Each resistance element has two terminals brought out through a resistance network to an electrical connector on the base of the probe. The resistance networks make it possible to interchange sensing elements without any loss of sensing accuracy.
 E.  The heating provision for deicing these probes is discussed in Pitot-Static and Temperature Probe Anti-Icing, 30-31-00.
　
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