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

An envelope is applied around the intended flight path: weather within
the envelope is considered Flight Path Weather; weather outside the
envelope is Secondary Weather. On the display, Secondary Weather is
distinguished from Flight Path Weather by black stripes. The flight path
angle is 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 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
necessary1 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 AUTO mode, the RDR-4000 projects a 3D 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 Flight 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 Secondary Weather. Stronger returns
outside the envelope (Secondary Weather) never override the strongest
returns displayed as Flight Path Weather.
1
At cruise altitudes above 29,000 feet, original versions of the radar maintained
the lower envelope boundary at 25,000 feet. Radar Processor units with later
software modifications (930-1000-002 SW version 1 and later, or 930-1000-003
all SW versions) adapt the lower boundary based on the weather detected
ahead of the aircraft. When no convective activity is detected, the envelope
remains +/- 4,000 feet. When the radar detects a convective cell which may
become relevant to the current flight path, the lower boundary near the cell is
extended to 25,000 feet.
RDR-4000 Technical Operation
56
IntuVue RDR-4000 Weather Radar Pilot's Guide
Envelope Boundary Limits
Lower Envelope Boundary
25,000 ft MSL or Flight
Altitude minus 4,000 ft.
Flight Altitude minus 4,000
(min. ground elevation)
Upper Envelope Boundary
Flight Altitude plus 4,000 ft
(max. 60,000 ft MSL)
10,000 ft MSL
060-4492-000
Rev 7, February 2015