3. When the flight and combined systems fail,
the backup flight control system performs as an
isolated system. Surface rates available at the rudder
and stabilizers are reduced by the limited output of the
backup pump. There is no flaperon actuator control.
The cockpit indicator will flicker out if the pilot
applies inputs to the controls that exceed the capacity
of the pump. The cockpit RUDDER THROW light
will also be illuminated, indicating that approximately
33 percent of normal rudder throw is available.
POWER ACTUATOR MAINTENANCE
Maintenance of primary flight control surface
power actuators is generally beyond the capability of
organizational maintenance-level activities. Removal
of hydraulic components and associated linkages on
the power actuators will destroy critical adjustments.
Readjustment requires special tooling, jigs, and other
equipment available only at intermediate- or
depot-level maintenance facilities. When a power
mechanism has been isolated as the cause for flight
system malfunction, it is removed. It is forwarded
with the accompanying paperwork to the supply
activity for disposition.
CONTROL SYSTEMS MALFUNCTIONS
There have been many cases reported in which,
after flight, pilots have found flight controls jammed
while the aircraft was on the ground. Because the
controls were freed by excessive pressure before an
inspection could be made, the causes for the jammed
condition could not be found. No positive corrective
action was taken before the aircraft were released for
In some cases, accidents occurred on such
aircraft shortly thereafter.
When an aircraft experiences a control
discrepancy during flight, a thorough investigation
should be conducted immediately. In cases where
aircraft have safely returned from a flight during
which a control discrepancy was experienced, a
thorough investigation is necessary. This investi-
gation must be made before further flight. All parts of
the affected control system should be inspected for
proper rigging, clearances, and potential causes for
interferences. All sealed units that are suspect must
be replaced. Primary cause factors that should not be
overlooked include maneuvers that have exceeded the
operational design of the control systems. Hydraulic
system contamination, corrosion and/or distorted or
disconnected linkage may have caused the problem.
Inadequate lubrication and external contamination in
the form of preservative compounds, such as grease
combined with dirt and dust, may have caused the
problem. An increasing number of flight control
system malfunctions are related to system contami-
nation, and this ever-important aspect of hydraulic
system maintenance should be given the attention it
Checking of system filters and con-
tamination inspection of suspected systems are within
the capability of organizational activities. If a system
is found to be contaminated, the source of
contamination must be eliminated and the system
cleaned by recycling or flushing in accordance with
instructions provided in the appropriate MIM.
Contaminated components must be replaced as
necessary to restore proper system operation.
Disposition instructions for removed hydraulic
components vary with the production status of the
aircraft model. Diligent care must be taken to retain
the component in the as-is condition, with no change
in adjustment, disassembly, or cleaning. If the
component has slides or pistons that are jammed, no
attempt to free them should be made.
The aircraft must not be released for further flight
until the cause has been determined and corrected. If
it is not readily apparent why the component
malfunctioned, you should submit a Hazardous
Material Report/Engineering Investigation request. If
the discrepancy cannot be duplicated or cause
determined, an appropriate entry must be made in the
Miscellaneous History section of the aircraft logbook.
Trouble analysis of the flight control systems
requires the same systematic approach as any other
In many instances, malfunctions
are written off with incorrect corrective actions on the
maintenance action form (MAF). The corrective
action, Could Not Duplicate, or Replaced Suspected
Component, often results in a repeat discrepancy or
loss of the aircraft. Thoroughness in determining the
cause of a malfunction cannot be overemphasized.
Trouble analysis of the flight controls will require
complete cooperation with other work centers that are
involved in the operational checkouts. Most flight
control systems have electrical input, as well as
mechanical input from autopilot, automatic flight
control systems, or stabilizing augmentation systems.
Inputs occasionally cause erratic and/or misleading
aircraft flight characteristics. Flight characteristics