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momentarily engaged to position the launch bar by press and hold of the NWS button. Additionally,
NWS is automatically disengaged when the nose landing gear transitions to WoffW during takeoff or
when power is removed from the FCCs.
2.7.2.2 Emergency High Gain NWS. With a FCS CH 2 or FCS CH 4 failure, normal nosewheel
steering is lost. Emergency high gain NWS can be regained by pulling the failed channel circuit
breaker, unlocking the wings, and momentarily pressing the nosewheel steering button.
When emergency high gain NWS mode is entered, NWS indications may
not be displayed on the HUD. As a result, inadvertent nosewheel steering
actuation may injure ground personnel.
2.7.3 Wheel Brake System. The aircraft's wheel brake system provides normal braking, anti-skid,
emergency braking, a parking brake, and main wheel anti-spin. Normal braking utilizes HYD 2A
pressure and is capable of functioning with a separate anti-skid system. The anti-skid system, when
enabled, provides maximum braking effectiveness on wet runways or during heavy braking by
preventing wheel skid. When selected, emergency braking utilizes HYD 2B pressure, if available, or
brake and APU accumulator pressure to provide backup braking capability following a HYD 2A
failure. The anti-spin function stops main landing gear wheel rotation prior to landing gear retraction.
2.7.3.1 Wheel Brake Assembly. Each main landing gear wheel is fitted with hydraulically actuated
multiple disk brakes. There are two independent sets of brake lines running to each wheel brake
assembly: the normal brake line pressurized by HYD 2A and the emergency brake line pressurized by
HYD 2B or the brake and APU accumulators. See figure 2-16. Only one set of brake lines can be
pressurized at any given time. A shuttle valve on each wheel brake assembly switches from normal to
emergency brake pressure, depending on which is applied.
Each wheel brake assembly has a brake wear indicator pin, located on the inboard side of the wheel.
When the brakes are applied and the indicator pin is flush or below flush with the brake housing, the
brake pads require changing.
Each wheel assembly incorporates a fuse plug which is designed to melt and deflate the tire at
temperatures below those which would result in a catastrophic tire blowout.
2.7.3.2 Wheel Brake Operation. Each main wheel brake is controlled by a separate brake pedal,
integrated into the rudder/brake pedal mechanism. Pilot applied force to the top of each brake pedal
is transmitted by a series of cables and pulleys directly to the brake control hydraulic servovalves,
located in the nose wheelwell. The amount of hydraulic pressure applied to the wheel brakes by the
servovalves is directly proportional to brake pedal force. Dual brake pedal action provides symmetric
braking, while individual brake pedal action provides differential braking. In the F/A-18F (trainer
configuration), a second set of cables are routed to the servovalves from the rear cockpit brake pedals.
The servovalves are controlled by the pilot applying the most brake pedal force.
A1-F18EA-NFM-000
I-2-47 ORIGINAL
2.7.3.3 Normal Braking. Normal braking is enabled when HYD 2A is operable and the EMERG
BRK handle(s) are in the stowed position. The emergency brake valve is closed and the emergency
brake lines are unpressurized. During normal braking, HYD 2A pressure is applied through the left and
right servovalves proportional to the amount of pilot applied brake pedal force and is routed to the
main wheel brakes. When the ANTI SKID switch is ON, the anti-skid system modulates pilot applied
brake pressure in order to prevent wheel skid. When the ANTI SKID switch is OFF, the pilot must
regulate brake pedal force to prevent wheel skid.
2.7.3.4 Anti-skid System. The anti-skid system performs 4 basic functions which are designed to
maximize braking effectiveness during landing rollout: touchdown protection, wheel spin-up override,
skid control, and locked wheel protection. The anti-skid system is enabled when the ANTI SKID
switch is ON and the LDG GEAR handle is DN.
The system contains two wheel speed sensors, an anti-skid control unit, and an anti-skid control
valve. The anti-skid control unit senses wheel speed and operates by electronically limiting the amount
of HYD 2A pressure that is applied to the wheel brakes through the anti-skid control valve and the
normal brake lines. Anti-skid is not available when emergency brakes are selected.
Touchdown protection delays initial brake application on landing by completely dumping brake
pressure until (1) weight is on the right main landing gear and wheel speed is over 50 knots or (2), if
a wet runway delays wheel spin-up, for 3 seconds after landing. This function prevents landing with
　
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本文鏈接地址：NATOPS Flight Manual 飛行手冊(cè) 1(53)