symbols from other displays were incorporated into the VSD. For
example, the symbol for MCP-selected altitude is the same shape
as the corresponding symbol on the primary flight display altimeter
Although the VSD can
be used to assess path stability, path stability is only part of
the equation for a stable approach. The other factor is speed stability.
To facilitate speed stability, a new symbol was introduced on the
VSD. The range-to-target speed symbol is a green dot that shows
where excess speed will be dissipated along the vertical flight
path vector. If excess speed is not an issue, then the symbol will
not appear on the display.
The display remains stable
during dynamic conditions. Flight crews should keep in mind that
the VSD is a supplementary display and as such is not intended for
use as the primary reference during dynamic maneuvers and procedures.
Incorporating the VSD
does not require any changes to flight operations procedures, except
for the addition of procedures that apply to the VSD in non-normal
conditions. Additions to the airplane flight manual describe the
features of the VSD. Flight crew training regarding the VSD only
involves written materials.
BENEFITS OF THE VSD
The main benefit of the
VSD is improved safety. The VSD will give flight crews an intuitive
view of the vertical situation just as the current map display provides
an intuitive depiction of the lateral situation. In conjunction
with the other safety features of the flight deck, this increased
vertical situation awareness helps prevent CFIT and approach and
landing accidents and incidents, thereby further decreasing the
already low accident rate of the worldwide commercial airplane fleet.
The VSD depicts terrain
information from the TAWS or other onboard sources from another
perspective. The TAWS generates a lateral view of the surrounding
terrain and provides terrain proximity alerting. The VSD depicts
the vertical dimension of the terrain (fig.
4), which will allow crews to recognize possible terrain conflicts
more readily, before a TAWS alert is generated.
The VSD also depicts
the final approach segment of the intended path of the airplane
to the runway (fig. 5),
thereby assisting flight crews as they establish the glide path.
Terrain alerting from the TAWS is disabled gradually during this
phase of flight to eliminate nuisance alerts, but the VSD is available
The VSD also complements
the increased use of constant-angle, area navigation, and required
navigation performance (RNP) approaches by providing immediate validation
of the selected approach path and allowing full-time monitoring
of the airplane position relative to the selected glide path. As
low-altitude, in-cloud maneuvering becomes commonplace and RNP criteria
allow better utilization of restricted airspace, the VSD will serve
as an invaluable confirmation of airplane performance.
The VSD will provide
additional operational benefits. Earlier recognition of terrain
clearance problems facilitates more timely go-arounds and earlier
CFIT avoidance. In addition, with improvements in vertical awareness,
flight crews have an improved ability to monitor the vertical path.
Earlier recognition of unstabilized approaches helps reduce the
number of go-arounds and missed approaches. Because many unstabilized
approach problems are manifested during the landing phase of flight,
earlier recognition also should reduce the number of hard landings,
runway overruns, brake fires, and tire failures. This will help
reduce airline operating costs by extending the life of the airframe
structure, landing gear system, tires, and brakes and by reducing
the airplane maintenance downtime associated with landing problems.
Finally, the intuitive
nature of the VSD will allow flight crews to assess the vertical
situation quickly, thus reducing overall workload. Crews will have
more time during the most critical phases of flightclimb,
descent, and final approachto focus on other routine tasks
and handle any unusual circumstances they may encounter.