Reference (or a fixed height for Barometric modes) and depends on the
actual collective mode engaged.
Further to the Safety Height there is also an Ultimate Fly-Up Limit, a fixed
height (not adjustable) which, if passed, will automatically cause the aircraft
to fly back up to this height or the Safety Height, if higher. The following table
gives the Safety Height Rad Alt limits and Ultimate Fly-Up Limit for the
different collective modes:
Hold
Mode Applicable Range Safety Height (ft
AGL)
Ultimate
Fly - Up
Limit
(ft AGL)
VS All conditions 150 ft 150 ft
ALTA All conditions 150 ft 150 ft
ALT
Airspeed less than 55 KIAS or
HOV 35 ft 35 ft
All other conditions 150 ft 150 ft
RHT
Airspeed less than
55 KIAS, HOV Variable *
15 ft
All other conditions 75 ft
* Safety Height ═ Rad Alt Reference - (7 + 1/8xRad Alt Reference)
When the collective Fly Up safety function is activated, due to an height
excursion below the Safety Height or Ultimate Fly-Up limit, the aural
message "ALTITUDE ALTITUDE" is triggered and a HTML message is
displayed on the PFD on the top left of the attitude indicator.
When the collective is automatically driven up, it is normally limited by the PI
limiting function. Should the relevant MUH limits be exceeded the PI limits
will be moved up as follows:
- Maximum 121% AEO for airspeeds below 60 KIAS
- Maximum 176% OEI for airspeeds below 60 KIAS
- Maximum 110% AEO for airspeeds above 60 KIAS
- Maximum 160% OEI for airspeeds above 60 KIAS.
CAUTION
WHEN DESCENDING OVER TERRAIN, WITH A COLLECTIVE
MODE ENGAGED AND AFTER A CONTINUOUS DESCENT OF AT
LEAST 2500 FT, AT APPROXIMATELY 2500 FT RAD ALT
HEIGHT, THE FLY UP SAFETY FUNCTION MAY ERRONEOUSLY
INTERVENE AND INCREASE THE PI TO ABOVE THE MCP
LEVEL. THIS CONDITION SHOULD BE CONTROLLED
MANUALLY WITH THE COLLECTIVE TO MAINTAIN THE PI
WITHIN THE MCP LIMITS UNTIL THE HTLM MESSAGE ON THE
PFD EXTINGUISHES.