Home' RTCA Documents for Review : Addressing Human Factors/Pilot Interface Issues Contents 47
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for Use by the Flightcrew, AC 23.1309-1() System Safety Analysis and Assessment
for Part 23 Airplanes, and AC 25-11() Electronic Flight Displays.
Retrofit Considerations: Integration Using Equipment from Multiple Suppliers
Multiple, independent alerting strategies from differing equipment used on that same flight
deck can drive an increase in visual scan and crew workload in interpretation of the system
status, as well as diluting the attention getting qualities of the alerts. In complex highly
integrated cockpits, the architecture of the sensors and systems drive loss of multiple
functions during failure modes often requiring more actions than desirable.
Specific Certification Issues
In some retrofit applications, the annunciation of GPS may be indicated by a
generic term such as “LRN” (long range navigation), which could refer to multiple
sensors depending on the level of integration of the sensor. Symbology and
annunciations used with basic sensors such as bearing pointers have been observed
to not be adequate for crew awareness of integrated navigation sensors state, for
example, FMS, GPS, and ILS/LPV.
An LPV capable FMS was unable to command a display to post an alert with the
loss of vertical navigation (VNAV) or GPS.
Highly integrated avionics typically produce failure events that result in multiple
system sensors being affected. Requiring the flightcrew to manually restore critical
functions by selecting redundant system sensors along with managing other tasks
has resulted in excessive pilot workload.
New or upgraded equipment provided alerting message information that was
different or independent from the existing, or legacy alerting message information.
Approved Design Examples
To annunciate integrated navigation sensors state, for example, FMS, GPS, and
ILS/LPV, there have been approved certifications and operations using additional
discrete annunciators in the flightcrews’ primary field of view, close to the primary
flight display, to indicate the selection and state of the navigation sensor in use.
To manage failures of a highly integrated system, automatic sensor source
reselection has also provided successful mitigation for restoring lost sensors, fault
isolation and failure recovery. Automatic sensor source reselection, along with
umbrella, or collector crew alerting messages, has been useful in reducing pilot
confusion and workload.
Text and labeling verbiage as well as color convention for added equipment
applied the existing flight deck alerting philosophy for systems monitoring and
failure alerting to leverage ease of understanding for the crew.
AC 25.1322-1, Flightcrew Alerting, contains information about failure
Consider providing separate annunciators in lieu of adding new information and
discretes directly into the PFD, when altering the PFD is economically impractical.
This method has met the intent of the mode awareness requirements in AC 20-
138() Airworthiness Approval of Positioning and Navigation Systems.
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