TM 55-1510-222-10Figure 3-26. Pilot’s Altitude Indicator (BA-141).routed to the Air Data Computer. The ADC recomputesall data on hand, sends corrected altitude pressureinformation to the Flight Director and autopilot, servocommands to correct the display on the pilot's altimeter,and applies altitude information to the transponder (fortransmission to ground stations).a.Controls/Indicators and Functions.(1) OFF Flag. Presence indicates loss of powerto instrument and unreliable readings.(2) ALT alert annunciator. Illuminates whenaircraft is within 1000 feet of preselected altitude duringcapture maneuver and extinguishes when aircraft iswithin 250 feet of preselected altitude. After capture,annunciator will illuminate if aircraft departs more than250 feet from the selected altitude.(3) Altitude Scale.Used with needle to indicateaircraft altitude in hundreds of feet. Subdivided into 20foot increments.(4) IN HG Indicator. Indicates local barometricpressure in inches of mercury. Adjusted by use ofBARO knob.(5) MB Indicator. Indicates local barometricpressure in millibars. Adjusted by use of BARO knob.(6) BARO Knob.Used to manually setbarometric pressure displayed in the MB and IN HGwindows.(7) Needle indicator. Used with altitude scale todisplay aircraft altitude in hundreds of feet.(8) Altitude counter drums.Indicates aircraftaltitude in tens of thousands, thousands, and hundredsof feet above sea level.NOTEIf the OFF flag is visible, either DCpower is off, the fuse has blown, orthere is an altimeter encoder failure.Since the OFF flag monitors only theencoder input to the altimeter andnot transponder condition, thealtitude reporting function may beinoperative without the OFF flagshowing, in the case of transponderfailure or3-81
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