Specifications

SECTION III
INSTRUMENTATION AND AVIONICS
MODEL 560
VNAV MODE
The vertical navigation mode (VNAV) mode provides a means to define a climb or descent path to a
vertical waypoint ahead of the airplane and to track the path to that waypoint. The waypoint is defined
based on a distance reference (bias distance) “TO” or “FROM” a short range VORTAC station waypoint, or
the next FMS waypoint if the FMS system is being used for navigation. Upon arrival at the waypoint/altitude
the mode automatically changes to altitude select (ASEL) capture mode and then to altitude hold (ALT)
mode when it levels at the selected altitude.
VNAV DEFINITIONS AND OPERATION
Desired Altitude (ALT) - The altitude at which the airplane will level at the completion of the climb or
descent.
Station Elevation (STA EL) - The elevation above sea level of the VORTAC station that the VOR and
DME are receiving. Does not apply to FMS waypoints when used for VNAV.
TO/FROM Bias (TO/FR) - The distance set into the VNAV that moves the point for completion of the
problem away from the VORTAC or FMS waypoint being used.
TO bias moves the point closer to the airplane than the VORTAC or FMS waypoint being used.
FROM bias moves the point farther from the airplane than the VORTAC or FMS waypoint being used.
During VNAV operation overspeed protection based on the V
MO
speed limit, and underspeed
protection based on a fixed 120 kts. will be provided. If either of these speeds is reached a special
submode will engage and will override the VNAV mode until the speed situation is corrected. If a deviation
of 1000 feet from the computed path occurs, VNAV mode will cancel. Single-point VNAV will remain armed
if another vertical mode is selected for early descent prior to path capture. After level-off, a descent away
from the altitude preselector will occur upon intercept of the programmed VNAV path. To prevent an
undesired descent after level-off, manually disarm the VNAV mode.
VNAV operation will be cancelled if another vertical mode is selected, the air data information from the
micro air data computer (MADC) becomes invalid, the DME signal is lost for five seconds, an overspeed or
underspeed as described above occurs, the PFD NAV source is changed, glide slope capture or level off at
the waypoint occurs, or in case of the detection of various system faults by the system monitors.
In order for VNAV mode to operate the airplane must be proceeding along a direct path towards or
away from the short range NAV (VORTAC) (or to the next FMS NAV waypoint) which has been selected as
a reference. If a VORTAC is being used, the VOR azimuth and DME must be locked onto the VORTAC
station for VNAV computation. The desired altitude, station elevation (VORTAC only) to the nearest 100
feet, and the TO/FROM bias (if required) must be set into the VNAV system. If the FMS is being used for
navigation, the next waypoint may be used, with or without TO or FROM bias, and station elevation (STA
EL) data is not required. Attempts to insert VNAV problems behind the airplane or outside the parameters
of the system will be ignored by the system.
Figure 3-20. To - From Bias
I 3-40 Configuration AA 56OMB-01