Home' RTCA Documents for Review : Addressing Human Factors/Pilot Interface Issues Contents 66
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different symbology shapes between flight path vector guidance versus pitch-
based guidance to ensure the crew recognizes the difference in guidance.
FD guidance (cues and modes) displayed in a dual PFD flight deck should be based
on the NAV source coupled to the designated flight guidance system. The PFD
provides clear information about the active NAV source, such as course deviation
indication. The non-coupled HSI can display NAV source indications different
from the coupled NAV source, such as left side CDI displaying deviations to the
FMS course, while the right side CDI can display deviations to the localizer. The
FD cues and mode annunciations displayed on the non-coupled PFD should be
based on the coupled PFD NAV source so that both pilots are monitoring the same
FD cues and modes.
Differences in airframe, flight guidance system, autopilot, and display
characteristics (such as expanded versus compressed pitch scale) should all be
considered as part of the design and testing effort. Successful implementations
have measured flight technical error (see AC 25-7()) gathered from fine tracking
tasks as well as recovery maneuvers (encountered with unusual attitude, ground
proximity, and traffic evasion) to substantiate the performance of new flight
guidance implementations to existing flight directors. High gain tasks close to
terrain are effective in demonstrating the usefulness of new flight guidance
symbology, and fine tuning flight director gains.
AC 25.1329-1(), Approval of Flight Guidance Systems
AC 27-1(), Certification of Normal Category Rotorcraft, Section AC 27.1329
AC 29-2(), Certification of Transport Category Rotorcraft, Section AC 29.1329
Retrofit Considerations: Automatic Flight Control System (AFCS) and Autopilot
(AP) Integration with Servos
Management of flight control transients are critical to maintaining safe flight path control.
While various means are available on modern flight decks to augment this control (such as
power boosted controls, autopilots, fly-by-wire), large excursions, or transients can occur
if the integration of the subsystems is not refined to match the other subsystem capabilities.
Disengagement of an autopilot should not result in a transient, or temporary loss of control,
per AC 25.1329-1() guidance. Even minor transients can result in nuisance mis-trim
alerting if the system is not adjusted appropriately.
Specific Certification Issues
If a servo can hold more force than a pilot can when the Autopilot is disengaged,
a transient can occur affecting flight path control, resulting in the pilot losing
awareness of the aircraft trim state.
Approved Design Examples
Full-time trim indication within or close to the pilot’s primary field-of-view
informs the pilot of the aircraft trim state during all phases of flight.
Consider existing system constraints in the design of the AFCS and AP and test all
transitions from automatic to manual flight path controls to evaluate whether
unacceptable transients exist during transitions to manual flight. Desktop
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