TM 1-1520-238-T-7
11–68
11–7.
SYSTEM DESCRIPTION (cont)
11–7
(d) In the manual mode (fig. 11–41) when airspeed is above 80 knots, control logic within the SCUs
open the circuit to the MAN SEL relay (K1-3/4) coil. Actuation of the stabilator manual control switch has no effect
on the stabilator. When airspeed decreases below 80 knots, control logic inside the SCUs cause internal contacts
to close, completing the circuit from the stabilator manual control switch through the relay coil of K1-3/4 and
normally closed (NC) contacts of relay K1-6. 28 VDC power is supplied through STAB MAN DC circuit breaker
(CB6) to the stabilator manual control switch. When either crew member places the NU/ND switch on the
stabilator manual control panel to NU, relay K1-3 energizes. At the same time, voltage passes through the NU
diode, SCU control logic, the relay coil of K1-3/4 and the normally closed (NC) contacts of relay K1-6, closing the
normally open (NO) contacts of relay K1-3/4, providing a holding circuit to the relay coil of K1-3/4. The NC
contacts of relay K1-3/4 open, de-energizing the AUTO MAN relay K1-1/2. When relay K1-1/2 opens, the NO
contacts open circuits from the SCUs to the cylinder assembly. Relay K1-1/2 NC contacts enable the MAN STAB
indicators on the pilot and CPG caution/warning panels and complete a manual mode circuit path to the stabilator
cylinder. The motors extend until the NU/ND switch is released or the extend limit switches are opened. When
either crew member places the NU/ND switch on the stabilator manual control panel to ND, relay K1-5 energizes.
At the same time, voltage passes through the ND diode, SCU control logic, the relay coil of K1-3/4 and the NC
contacts of relay K1-6, closing the normally open (NO) contacts of K1-3/4, providing a holding circuit to the relay
coil of K1-3/4. The NC contacts of relay K1-3/4 open, de-energizing the AUTO MAN relay K1-1/2. When relay
K1-1/2 opens, the NO contacts open circuits from the SCUs to the cylinder assembly. The NC contacts of relay
K1-1/2 enable the MAN STAB indicators on the pilot and CPG caution/warning panels and completes a manual
mode circuit path to the stabilator actuator. The motors will retract until the NU/ND switch is released or the retract
limit switches are opened. When the stabilator manual control switch is released to the OFF position, the MAN
STAB indicators remain on due to the holding circuit which keeps relay K1-3/4 energized. Depressing the RESET
pushbutton on the collective stick supplies 28 VDC through the ENG WARN circuit breaker (CB52) to energize
relay K1-6. Relay K1-6 NC contacts open, removing the holding circuit from relay K1-3/4. Automatic mode is
restored and the MAN STAB indicators go out.
