TM 1-1520-238-10 2-49 2.37.8   Stabilator  System. A  variable  angle  of  inci- dence  stabilator  is  installed  to  enhance  helicopter  han- dling characteristics. The stabilator is designed so that it will automatically be positioned by stabilator control units. These units determine stabilator position from airspeed, pitch rate, and collective stick position inputs. Automatic stabilator  range  of  travel  is  from  5°  trailing  edge  up through 25° trailing edge down. Manual control is from 10° trailing edge up to 35° trailing edge down. The stabilator is driven  by  two  independent  dc  motors.  Stabilator  opera- tion, in either manual or automatic mode, requires both ac and dc power supplies. Associated crew station controls and indicators are as follows: a.   Stabilator  Circuit  Breakers. The  stabilator  re- ceives 115 vac from the No. 1 essential ac bus through the STAB MAN AC and STAB AUTO AC circuit breakers. It also  receives  28  vdc  from  the  No.  1  essential  dc  bus through the STAB MAN DC circuit breaker and from the No. 3 essential dc bus through the STAB AUTO DC circuit breaker. These circuit breakers are on the pilot overhead circuit breaker panel. b.   Stabilator Manual Control Switch. The stabila- tor manual control switch is located on the stabilator con- trol panel (fig 2-26) installed inboard and forward of the friction grip on each collective stick. The switch, nose up (NU), and nose down (ND), permits crewmembers to con- trol the stabilator angle of incidence. The manual mode will  disengage  both  the  normal  auto  and  NOE/APRCH modes below 80 KTAS. Selection of the manual mode will cause the pilot and CPG MAN STAB caution lights to illu- minate. Transitioning above 80 KTAS in the manual mode will result in automatic switchover to auto mode. Failure of the automatic switchover to auto mode will result in the fol- lowing: (1)   Pilot and CPG MASTER CAUTION light starts flashing. (2)   Pilot  and  CPG  caution/warning  MAN  STAB light starts flashing. (3)   Stabilator aural tone is heard. Below 80 KTAS automatic mode is regained after selec- tion of manual mode by momentarily pressing the auto- matic operation/audio tone RESET button on either col- lective stick. c.   NOE/APRCH Switch. The NOE/APRCH switch, located on the ASE control panel (fig 2-27), positions the stabilator  at  25  degrees  (trailing  edge  down)  below  80 KTAS. If auto mode is on, this mode is selectable at any speed from a magnetically held switch. Transitioning past 80 knots will result in normal stabilator scheduling. Failure to revert to normal stabilator scheduling will result in the following: (1)   NOE/APRCH  switch goes to OFF. (2)   Pilot and CPG MASTER CAUTION light starts flashing. (3)   Pilot  and  CPG  caution/warning  MAN  STAB light starts flashing. (4)   Stabilator aural tone comes on. Regaining auto mode after the NOE/APRCH mode is se- lected is accomplished by momentarily pressing the auto- matic operation/audio tone RESET button on either col- lective  stick  or  setting  the  NOE/APRCH  switch  to  OFF. Manual mode may be regained by selecting manual mode with the NU/ND switch. d.   Stabilator  Position  Indicator. The  STAB  POS DEG indicator (fig 2-28), located in the upper right section of the pilot and CPG instrument panels, provides a visual indication of stabilator angle of incidence in either manual or automatic modes of operation. It is calibrated from 10° trailing  edge  up  to  35°  trailing  edge  down  to  reflect  the position of the stabilator trailing edge. An OFF flag is dis- played on the indicator face when the instrument is not op- erating and dc electrical power is applied to the indicator. With ac or dc power loss, both the OFF flag and pointer are not displayed. M01-311 POS STAB DEG Figure   2-28. Stabilator Position Indicator e.   Stabilator  Placard. A  placard  installed  to  the right of the position indicator in each crew station lists sta- bilator  incidence  angles  for  given  airspeeds.  Refer  to Chapter 5 for limitations.