(f)  Set ALT SEL control to 4000 feet. Check that no alert signal occurs.
 NOTE: The altitude alert computer rate detector inhibits the
____ alert output for 2 seconds when the selected altitude is changed at a rate greater than 1000 |333 feet/sec.
 (g)  Open landing gear DIS & CONT and ALT DIS & CONT circuit breakers on panel P12. Check that landing gear down annunciators go off.

 EFFECTIVITY

 

 ALL  16 Page 503  Sep 25/9434-16-00
 (h)  Slowly increase CADC altitude to 5500 feet. Monitor first officer's altitude indicator and check that alert signals occur as follows: 1) At 3100 | 100 feet, aural warning module sounds for 2
 | 1/2 seconds and annunciators come on. 2) At 3700 | 100 feet, annunciators go off. 3) XA all except AF 121, 122, 157, 161, 183, 184;
 at 4350 | 150 feet, aural warning module sounds for 2 | 1/2 seconds and annunciators come on flashing.
 4)  AF 121, 122, 157, 161, 183, 184; at 4350 | 150 feet, aural warning module sounds for 2 | 1/2 seconds and annunciators come on flashing.
 5)  XA all except AF 121, 122, 157, 161, 183, 184; at 4950 | 150 feet, flashing annunciators go off. 6) XA 121, 122, 157, 161, 183, 184; at 4900 | 150 feet, flashing annunciators go off.
 (i)  Close landing gear PRIM DIS AND CONT and ALT DIS AND CONT, and ALTIT ALERT MON circuit breakers.

 (5)  Restore airplane to normal.
 (a)  
Slowly relieve pitot-static system pressure.

 (b)  
Disconnect pitot-static test set (Ref 34-11-00).

 (c)  
Remove electrical power if no longer required (Ref 24-22-00).

 EFFECTIVITY

 

 ALL  07 Page 504  Sep 25/9434-16-00
 MAGNETIC HEADING REFERENCE SYSTEM - DESCRIPTION AND OPERATION
_____________________________________________________________

 1.  General (Fig. 1)
_______
 A.  The Magnetic Heading Reference System (MHRS) provides gyro stabilized magnetic heading information to the airplane flight instruments and interfacing systems. Two separate systems are installed in the airplane.
 B.  One complete system consists of a magnetic field sensor, a magnetic compensator, a compass coupler, a compass controller, and a radio-magnetic indicator (RMI) (Fig. 1). Magnetic heading is also displayed on compass cards in the two horizontal situation indicators (HSI).
 C.  The airplane magnetic heading displayed on the RMI's and HSI's is also applied to other airplane systems. Fast synchronization of the flight instrument compass cards (700 degrees per minute) is accomplished when power is first applied, the platform heading input is switched to a new source, or the operating mode is changed.
 D.  The MHRS provides two modes of operation, the SLAVED mode and the DG mode.
 (1)  
The SLAVED mode of operation is normally used at latitudes up to approximately 65 degrees where magnetic compass information is generally reliable. In this mode the magnetic heading output from the magnetic field sensor is synchronized with the inertial platform heading output from the inertial navigation system (INS). The SLAVED mode, in effect, provides inertial platform stabilized heading information with magnetic sense. The slaved mode offers long-term heading stability within its latitude range.

 (2)  
The DG mode of operation is normally used at latitudes higher than 65 degrees because of large and unpredictable magnetic errors encountered at the higher latitudes. In this mode, system input information is limited to inertial platform heading from the inertial navigation unit. Heading accuracy is dependent upon errors inherent in the inertial platform system and is irrespective of magnetic field variations. The DG mode offers only short-term heading stability, therefore heading information in this mode must be frequently updated to maintain its integrity.

 E.  The MHRS interfaces with the flight instruments and other airplane systems through the flight instrument switching network as shown in figure 2.
 (1)  
The magnetic heading signal is compensated for magnetic error and applied to the compass coupler, where it is synchronized with the platform heading signal from the INS. The magnetic heading output is applied to the autopilot system, and through flight instrument switching to the radio magnetic indicator (RMI) and horizontal situation indicator (HSI). The magnetic heading is supplied to the autopilot/flight director system (22-10-00) where it is resolved with a heading select signal to form a preset heading error signal.
　
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