SYSTEM DESCRIPTION (cont)
(e) The tail wheel lock control valve (fig. 716) is a two position threeway solenoid operated valve,
controlling hydraulic pressure to the tail wheel lock actuator. The TAIL WHEEL lock control panel supplies
28 VDC from the TWHL LK circuit breaker to the valve. When the tail wheel lock switch is placed in the LOCK
position, the control valve is deenergized and bypasses hydraulic fluid from the lock actuator to the return line.
Spring tension overcomes hydraulic pressure, locking the tail wheel. When the tail wheel lock switch is placed in
the UNLOCK position, the control valve is energized. This closes the return line and applies hydraulic pressure.
Hydraulic pressure overcomes spring tension, unlocking the tail wheel. A proximity switch is activated and lights
the TAIL WHEEL UNLOCK advisory indicator. The emergency hydraulic shutoff valve shuts off the flow of utility
hydraulic pressure to the directional servocylinder and tail wheel lock control valve when the low level switch is
activated. During normal operation, the emergency hydraulic shutoff valve is open, allowing pressure to flow from
the utility manifold to the directional servocylinder and the tail wheel lock control valve. When the low level switch
is actuated, a 28 VDC signal closes the emergency hydraulic shutoff valve. The fluid prevented from flowing is
conserved for use by the main rotor flight control servocylinders.