Figure 2-5-3. Advanced Flight Control System Panel

TM 1-1520-240-10 2-5-5 (1) HDG Switch. The HDG (heading) switch is used in conjunction with the CMD SEL switch either HSI MODE SELECT panel and the heading bug on either HSI to select coupled turns. The switch can be used only when airspeed is above 40 knots. When the switch is pressed and either CMD SEL switch is pressed, the heli- copter will automatically turn to and capture the heading bug on the selected HSI. In addition, the ENGAGED legend will illuminate. The switch is disengaged by press- ing it again. Heading intercept will be at standard rate of 3_ per sec- ond up to a bank angle limit of 20_ at 133 knots. The helicopter must be trimmed before engaging the mode and cyclic stick control inputs should be avoided except for longitudinal AFCS trim inputs to adjust airspeed. Figure 2-5-3. Advanced Flight Control System Panel Heading select is disengaged if either CENTERING DE- VICE RELEASE switch is pressed. (2) BARO ALT and RAD ALT Switches. The BARO ALT and RAD ALT are used to select altitude hold mode. An interlock prevents both switches from being engaged at the same time. When pressed, the EN- GAGED legend will illuminate. RAD ALT hold is used below 1,500 feet AGL. BARO ALT hold is used in forward flight to maintain a constant cruise altitude or may be used in HOGE. b. SYSTEM SEL Switch. The SYSTEM SEL switch is a five position rotary switch labeled OFF, 1 BOTH, 2 OFF. Normally, the switch is at BOTH. In this position, both AFCS are operating at one-half gain. If one system should fail, the good system is selected and that system operates at 3/4 gain. At OFF, both systems are inopera- tive except for CYCLIC TRIM. c. CYCLIC TRIM Switches. The AUTO and MANU- AL switch selects the mode of cyclic trim operation. The FWD and AFT switches are used to extend or retract the appropriate cyclic trim actuator. (1) AUTO and MANUAL switch. A two-position switch which is normally placed in AUTO. (a) AUTO Mode. In this mode, No. 1 AFCS controls the forward actuator and the No. 2 AFCS con- trols the aft actuator. (b) MANUAL Mode. In this mode, the ac- tuator can be controlled with separate FWD and AFT actuator control switches, using the airspeed indicator and CYCLIC TRIM indicators. (2) FWD and AFT switched. Three- position switched that can be placed in the EXT (extend) or RET (retract) position. These switches are spring-loaded to the center off position. If the cyclic trim actuators fail to extend or retract as indicated on the CYCLIC TRIM indi- cators, MANUAL mode can be selected. 2-5-16. Cyclic Trim Indicators. WARNING If the longitudinal cyclic trim actuators fail at the full retract position or are manually selected to the full retract position, do not exceed the airspeed limitations shown in fig. 5-7-1. The FWD and AFT CYC (cyclic) TRIM indicators (fig. 2-5-4) are on the center instrument panel. The indicators are labeled 60 RET, GND, 150 EXT. The indicators dis- play position of the forward and aft LCT actuators relative to airspeed. During ground operations, the pointer will be at GND to indicate activation of the landing gear proximi- ty switches. 2-5-17. AFCS OFF Caution. Two AFCS OFF caution capsules are on the master cau- tion/advisory panel ( 712 ,fig. 2-14-5, 714A , fig. 2-14-6). They are labeled 712 NO. 1 AFCS OFF and NO. 2 AFCS OFF, 714A AFCS 1 and AFCS 2. These cautions will illuminate when the associated AFCS is manually shutoff or has failed or the associated DASH is in a low rate condition. Refer to Chapter 8 AFCS Off Flight Characteristics.