TM 1-1520-240-102-14-2 warning symbol will appear on the 10,000 foot counter.Power to operate the AIMS altimeter is supplied by theNo. 2 DC bus through the NAV AIMS ALT circuit breakeron the No. 2 PDP.A barometric pressure setting knob is provided to insertthe desired altimeter setting in inches of Hg. A vibratorFigure 2-14-2. AIMS Altimeterpowered by No. 2 DC bus is contained in the altimeterand requires a minimum of 1 minute warmup beforechecking or setting the altimeter. If DC power to the alti-tude encoder is lost, a warning flag placarded CODEOFF appears in the upper left instrument dial.The flag indicates that the altitude encoder is inoperativeand that the system is not reporting altitude to groundstations. The CODE OFF flag monitors only the encoderfunction of the altimeter. It does not indicate transpondercondition. The AIMS altitude reporting function can beinoperative without the CODE OFF flag showing, as incase of transponder failure or improper control settings.It is also possible to get a good Mode C test on thetransponder control with the CODE OFF flag showing.Display of the CODE OFF flag only indicates an encoderpower failure or a CODE OFF flag failure. In this event,check the DC power is available and the circuit breakersare in. If the flag is still visible, radio contact should bemade with a ground radar site to determine whether theAIMS altitude reporting function is operative. The re-mainder of the flight should be conducted accordingly.2-14-7. Preflight Operation - AltimeterIf the AIMS altimeter encoding function is to be usedduring flight, perform the following steps before takeoff:CAUTIONIf the baroset knob binds or sticks, do notuse excessive force to set the altimeter.Excessive force can damage altimetergears, resulting in altimeter error. Settingscan sometimes be made by backing off theknob and turning at a slower rate.a.Set the pilot’s altimeter to the field barometricsetting.b.Check that the pilot’s altimeter indicates within 70feet of field elevation. If the altimeter error is greaterthan 70 feet, do not use the altimeter IFR flight.2-14-8. In Flight Operation - Altimeter.Operate the AIMS altimeter function as follows:a.Be sure the IFF set is on and set to the propercode.b.Be sure the altimeter is set to the local altimetersetting.c.Set the M-C (mode c) switch on the IFF controlpanel to ON.d.Check that the red CODE OFF flag is not visiblein the pilot’s altimeter.The copilot’s altimeter is a pneumatic counter-drum-pointer type which displays altitude in the same manneras the pilot’s altimeter. It also incorporates a barometricpressure setting knob and an internal vibrator poweredby the No. 2 DC bus. A minimum of 1 minute of vibratoroperation is require before setting or checking the altime-ter.At ambient pressure, both altimeters should agree within70feet of the field elevation when the proper barometricpressure setting is set in the altimeter. If the internalvibrator of either altimeter becomes inoperative due toDC power failure, the pointer drum may momentarilyhang up when passing from 9 through 0 (climbing) orfrom 0 to 9 (descending). This will cause a lag of magni-tude which will depend on the vertical velocity of theaircraft and the friction in the altimeter.2-14-9. Radar Altimeter (AN/APN-209A).Radar altimeters are provided for the pilot and copilot (fig.2-14-3). The altimeters provide a continuous indicationof the height of the helicopter above the surface from 0to 1,500 feet. Altimeter indications are reliable with pitchand roll attitude up to 45_.Altitude is displayed by a dial, pointer, and a digital dis-play. Each altimeter has HI and LO caution lights. Thecaution lights on each altimeter can be set independentlyof the other altimeter. The caution lights are set by rotat-ing the LO SET and H SET knobs until the L index andH index on the perimeter of the altimeter are at the de-sired altitudes.
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