190-00709-00 Rev. A
Garmin G1000 Pilot’s Guide for the Socata TBM 850
6-29
HAZARD AVOIDANCE
6.2 AIRBORNE COLOR WEATHER RADAR
SYSTEM DESCRIPTION
The Garmin GWX 68 Airborne Color Weather Radar is a four-color digital pulsed radar with 6.5 kilowatts
of output power. It combines excellent range and adjustable scanning profiles with a high-definition target
display. The pulse width is four microseconds (µs) on all ranges except the 2.5 nm range. The GWX 68 uses a
one µs pulse width at this range to reduce the targets smearing together on the display for better target definition
at close range.
The Socata TBM 850 uses a 10-inch phased array antenna that is fully stabilized to accommodate 30º of pitch
and roll.
To focus radar scanning on specific areas, Sector Scanning offers pilot-adjustable horizontal scan angles of
20º, 40º, 60º, or 90º. A vertical scanning function helps to analyze storm tops, gradients, and cell buildup
activity at various altitudes.
Radar features include:
• Extended Sensitivity Time Constant (STC) logic that automatically correlates distance of the return echo with
intensity, so cells do not suddenly appear to get larger as they get closer.
• WATCH™ (Weather ATtenuated Color Highlight) helps identify possible shadowing effects of short-range
cell activity, identifying areas where radar return signals are weakened or attenuated by intense precipitation
(or large areas of lesser precipitation) and may not fully reflect the weather behind a storm.
• Weather Alert that looks ahead for intense cell activity in the 80-320 nm range, even if these ranges are not
being monitored.
PRINCIPLES OF PULSED AIRBORNE WEATHER RADAR
The term RADAR is an acronym for RAdio Detecting And Ranging. Pulsed radar locates targets by transmitting
a microwave pulse beam that, upon encountering a target, is reflected back to the radar receiver as a return
echo. The microwave pulses are focused and radiated by the antenna, with the most intense energy in the
center of the beam and decreasing intensity near the edge. The same antenna is used for both transmitting and
receiving. The returned signal is then processed and displayed on the G1000 MFD.
Radar detection is a two-way process that requires 12.36 µs for the transmitted microwave pulses to travel out
and back for each nautical mile of target range. It takes 123.6 µs for a transmitted pulse to make the round trip
if a target is ten nautical miles away.
Airborne weather radar should be used to avoid severe weather, not for penetrating severe weather. The
decision to fly into an area of radar targets depends on target intensity, spacing between the targets, aircraft
capabilities, and pilot experience. Pulse type weather radar detects only precipitation, not clouds or turbulence.
The display may indicate clear areas between intense returns, but this does not necessarily mean it is safe to fly
between them. Only Doppler radar can detect turbulence.
Airborne weather radar has other capabilities beyond weather detection. It also has the ability to detect and
provide distance to cities, mountains, coastlines, rivers, lakes, and oceans.
