System Overview
1-11
If the autopilot is not engaged in any Autopilot or Flight Director
modes and is in the standby condition, as indicated by the green
“
AP READY
” annunciator on the PFD and no green or cyan lights
on the autopilot control head, Full-time Envelope Alerting is still
active. In this case, there are no flight director command bars
present and no autopilot mode annunciators aside from the “
AP
READY
” one along the top edge of the PFD.
If an underspeed condition is recognized, an “
UNDERSPEED
”
text alert is displayed along the top edge of the PFD pages and a
“CAUTION, UNDERSPEED” aural alert is played in the headsets
and is repeated approximately every 6 seconds until the condition
is no longer valid. The trigger for this Envelope Alerting
underspeed alert is when the system has determined 1.2V
s
has
been reached. Flap position, bank angle and g-loading are taken
into account to define V
s
at any point in time. One common
scenario this capability is designed to alert against is a traffic
pattern stall.
Similarly, on the high-speed end of the spectrum with the
autopilot in the standby condition (green “
AP READY
” along the
top strip of the PFD pages), if an overspeed condition is
recognized, a “
OVERSPEED
” text alert is displayed along the top
edge of the PFD pages and a “CAUTION, OVERSPEED” aural
alert is played in the headsets and is repeated approximately
every 6 seconds until the condition is no longer valid. The trigger
for this Envelope Alerting overspeed alert is when the system has
determined V
ne
is about to reached.
NOTE
Triggering of Overspeed Alerts
Full-time Envelope Alerting provides overspeed
alerting as Vne is approached. The software uses a
combination of speed rate, pitch rate, bank and
indirectly, g-onset rate to determine when to issue
the alarm. If it detects the aircraft is actually
recovering as speed approaches Vne, the
overspeed alert may be delayed until right at, or
slightly over, Vne.
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