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· Loss of either HYD 1 or HYD 2 due to engine failure or hydraulic
pump failure does not effect flight control with flaps AUTO; however,
failure of either HYD 1 or HYD 2 with flaps in HALF or FULL may
cause uncommanded but controllable yaw and roll transients as the
switching valves cycle. These yaw and roll transients may last 3 to 6
seconds.
· To prevent repeated switching valve cycling, avoid stabilized flight
where engine windmill rpm results in hydraulic pressure fluctuations
between 800 and 1,200 psi.
11.4.2 Leading Edge Flap Asymmetry. Leading edge flap asymmetries can occur when one of the
LEF hydraulic drive units (HDU) stalls/fails or the mechanical interconnect between the inboard and
outboard LEF surfaces fails. The most common LEF asymmetry results from a weak LEF HDU that
stalls (stops moving due to aerodynamic loading) during abrupt longitudinal maneuvers at high
airspeed and low altitude. When this happens, a roll-off away from the failing HDU as AOA or g is
increased followed by an abrupt roll-off in the opposite direction is typical. Failure detection logic in
the FCS software is designed to provide advanced warning of a LEF asymmetry; however, during
extremely abrupt maneuvers, an HDU stall may not be detected in time to allow the pilot to abandon
the maneuver and avoid a large roll transient. When a LEF asymmetry due to an HDU stall is detected,
a FLAP SCHED caution is displayed until LEF command and position agree, a ²FLIGHT CONTROLS,
FLIGHT CONTROLS² voice alert sounds, and a 256 BLIN code is displayed on the FCS
status page. When g and AOA are reduced until the LEF command and position agree, the FLAP
SCHED caution is removed but the 256 BLIN code remains on the FCS status page.
A1-F18EA-NFM-000
IV-11-9 CHANGE 1
Avoid high-g maneuvers at low altitude if an HDU stall has been detected during the flight (BLIN
256 on the FCS status page) even if the FLAP SCHED caution has cleared. BLIN 256 indicates a
weak/failing HDU that may result in very large roll transients and/or over-g during high-g maneuvers.
11.4.3 Stabilator Failure. Since there is no mechanical reversion mode of the flight controls, the FCS
control laws automatically reconfigure in each axis to allow continued flight in the event of a single
stabilator failure. This failure mode, known as stabilator reconfiguration, or STAB RECON, is
designed to compensate for the loss of the contribution of the failed stabilator to pitch and roll control.
This is accomplished by disabling differential stabilator commands and using the other rolling surfaces
to counter the roll and yaw moments produced when the remaining stabilator responds to pitch axis
commands. Flight tests demonstrated excellent handling qualities with a stabilator failed off during
maneuvering flight and aerial refueling. The pitch axis is slightly sluggish, maximum roll rate is
noticeably lower, and roll coordination is slightly degraded.
In UA, with a failed stabilator, maximum roll rate is extremely low in the
transonic region below 20,000 feet, especially when rolling away from the
failed side. Significant roll and yaw coupling may occur with forward stick
inputs at Mach >1.4 and altitude >30,000 feet.
The degradation in roll coordination is characterized as a small amount of sideforce during lateral
inputs with flaps AUTO and noticeable sideslip with flaps HALF. Configuration changes exhibit a
slight roll toward the failed stabilator when transitioning from flaps AUTO to flaps HALF; away from
the failed stabilator when transitioning from flaps HALF to flaps AUTO. Flight tests demonstrated
that flight with a stabilator failed in flaps HALF was nearly transparent to the pilot from a handling
qualities perspective during normal approaches, waveoffs, and FCLP or flared landings. A small but
controllable yaw away from the failed stabilator is apparent at touchdown. Additionally, pitch stick
inputs during the landing roll complicate directional control and should be avoided.
Extending the speedbrake may produce uncommanded roll into the failed stabilator. The uncommanded
roll is more pronounced at low speed flight conditions due to the reduced aileron effectiveness
at the large trailing edge up aileron deflections commanded by the speedbrake function. The roll can
be balanced with lateral stick deflection.
In UA, with a failed stabilator, nose down pitching moment capability is degraded at low to moderate
airspeeds, especially for aft center of gravity and heavy wing store loadings. A safe level of nose down
pitch capability is available for flight below 10° angle of attack.
In UA, with a failed stabilator, do not exceed 10° AOA due to reduced
nose down pitch authority.
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本文链接地址：
NATOPS Flight Manual 飞行手册 2(10)
