AIRPLANE
OPERATIONS
MANUAL
CREW
AWARENESS
REVISION 39
2-04-35
Page
1
Code
01
AOM-145/1114
WINDSHEAR DETECTION AND ESCAPE
GUIDANCE SYSTEM
The EMB-145 is equipped with an additional warning system
dedicated to windshear detection. The system provides visual and
aural alarms to warn pilots of a windshear occurrence, as well as the
most appropriate maneuver to recover from such phenomenon.
The Windshear Detection function is performed by the EGPWS
computer, which also performs ground proximity warning functions.
The Windshear Escape Guidance is a Flight Director mode provided
by the avionics package.
WINDSHEAR GENERAL INFORMATION
Windshear is a sudden change in wind direction or speed, normally
caused by thunderstorms, frontal systems or any topographical feature
that may affect the wind flow (e.g. hills, mountains, lakes, seas etc...).
Due to ground proximity, the most hazardous phases of flight
regarding windshear encounters are takeoff, approach and landing.
On a windshear, wind may shift from a tailwind to a headwind or to a
downdraft or updraft. The consequences may be an abrupt change in
airspeed, lift and altitude, upwards or downwards, according to shifting
direction. Although quick, windshear is not instantaneous, which may
lead pilots to correction attempts in the wrong manner. For instance,
an airplane facing a headwind after takeoff, appears to have good
performance, characterized by high airspeed, which drives the pilot
into rotating the airplane to a pitch higher than usual. When the
thunderstorm core is reached, wind shifts to a downdraft and airspeed
decreases, as well as vertical speed. The pilot’s natural reaction is to
lower the airplane’s nose in an attempt to maintain airspeed. Further
ahead, wind shifts to tailwind component, resulting in a dramatic
airspeed reduction with the nose already down. Under such scenario,
it is very difficult to maintain a positive rate of climb.
If the takeoff or landing can not be delayed, the correct action is to
increase airspeed before being subjected to windshear encounter and
to consider flying near stall speeds with high angle of attack if
necessary to regain altitude.
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