TCAS791
Principles of Operation
Pilot’s Guide 3-3
• The intruder aircraft approaches your aircraft on a collision course
that will intercept your aircraft within 15 or 20 seconds (within
15 seconds for a non-altitude reporting intruder aircraft; within
20 seconds for an altitude reporting intruder aircraft).
When It’s Used
The TCAS791 uses sensitivity level A in the following situations:
• Your aircraft has a radio altimeter and is below 2,000 ft AGL.
• Your aircraft does not have a radio altimeter but its retractable
landing gear is in the down position.
Sensitivity Level B
Definition
Sensitivity level B consists of two criteria for displaying a TA:
• The intruder aircraft enters into a hockey puck shaped area sur-
rounding your aircraft defined by a 0.55 nmi horizontal radius
and a height of ±800 ft from your aircraft. (See figure 3-1.)
OR…
• The intruder aircraft approaches your aircraft on a collision course
that will intercept your aircraft within 20 or 30 seconds (within
20 seconds for a non-altitude reporting intruder aircraft; within
30 seconds for an altitude reporting intruder aircraft).
When It’s Used
The TCAS791 uses sensitivity level B in the following situations:
• Your aircraft has a radio altimeter and is above 2,000 ft AGL.
• Your aircraft does not have a radio altimeter but its retractable
landing gear is in the up position.
• Your aircraft does not have a radio altimeter and has fixed land-
ing gear.
Audio Inhibit, TCAS791
This audio inhibit feature prevents the aural part of TAs, “traffic traffic,”
from being announced during takeoff and landing in order to minimize
pilot distraction. The corresponding TA symbols will still be displayed.
When It’s Used
The TCAS791 uses this audio inhibit feature in the following situa-
tions:
• Your aircraft has a radio altimeter and you’re below 400 ft AGL.
• Your aircraft does not have a radio altimeter but its retractable land-
ing gear is in the down position.
