Envelope Boundary Definition - Honeywell IntuVue RDR-4000 Pilot's Manual

The separation is done by applying an envelope around the intended
flight path: weather within the envelope is considered on path weather;
weather outside the envelope is off path weather. On the display, off
path weather is distinguished from on path weather by black stripes
(see illustration on page 34). The flight path angle is computed based
on the ratio of calculated vertical speed to ground speed. The expected
flight path altitude is extrapolated to 60 nm. Beyond 60 nm, level flight
at the calculated altitude is assumed.

ENVELOPE BOUNDARY DEFINITION

The upper and lower boundaries of the separation envelope are based
on the parameters listed above. The envelope is not bounded in the
horizontal plane. During level flight the envelope extends from 4,000 ft
above to 4,000 ft below the aircraft's altitude. At cruise altitudes above
29,000 ft MSL, the lower boundary is extended down to 25,000 ft MSL
when necessary to ensure that the most reflective parts of any
convective cells are displayed. The upper boundary cannot go lower
than 10,000 ft MSL. Additionally, absolute envelope boundaries of
60,000 ft and ground level apply. The resulting rules are shown in the
following table.
Aircraft Altitude
(ft MSL)
> 29,000
29,000 to 6,000
< 6,000
In the ALL/ALL WX and ON PATH/PATH WX modes, the RDR-4000
projects a three-dimensional memory space onto a two-dimensional
display. This means the weather displayed for any one memory cell is
the color of the strongest return in that column of memory cells.
Specifically, if there is any weather data in a given column that is inside
the envelope for on path weather; the color of the strongest of these
returns is displayed. If there is no weather data inside the envelope,
then the color of the strongest return from outside the envelope is
displayed as off path weather if in the ALL/ALL WX mode. In the ON
PATH/PATH WX mode, no off path weather is displayed.
Stronger returns outside the envelope (off path weather) never override
the strongest returns displayed as on path weather.
Technical Operation
54
IntuVue RDR-4000 Weather Radar Pilot's Guide
Envelope boundary limits
Lower Envelope Boundary
25,000 ft MSL or Flight
Altitude minus 4000 ft
Flight Altitude minus 4,000 ft
(min. ground elevation)
Upper Envelope Boundary
Flight Altitude plus 4,000 ft
(max. 60,000)
10,000 ft MSL
D201002000008
Rev 1, December 2014