CHAPTER 20
Extreme Weather Procedures
20.1 ICE AND RAIN
Before flight, check with the weather service for the location of the freezing level and probable icing
conditions. Flight through known or suspected icing conditions should be avoided, if possible, to
prevent engine FOD from ice ingestion.
Prolonged flight in icing conditions is an emergency situation. Flight duration which allows a
noticeable accumulation of ice (more than 3/8 inch) on the LEFs constitutes prolonged flight. Ice forms
rapidly on the inlet lip and, if allowed to accumulate, can be drawn into the engine causing compressor
stalls and/or major FOD. Severe icing conditions can result in rapid ice accumulation in a very short
time. An INLET ICE caution should serve as a warning to take action to avoid further ice
accumulation.
If icing is anticipated or encountered -
1. Perform an engine anti-ice detector test (ENG ANTI ICE - TEST) to verify proper detector
operation.
20.1.1 Ground Operation.
If ambient temperature between 0 and 7¡C -
1. Minimize engine operation above IDLE to reduce the potential for ice accumulation on the engine
inlet lips. Inlet lip icing can occur at these conditions without the INLET ICE caution.
If visible moisture exists (rain, fog) and the temperature is 45¡F (7¡C) or less -
1. ENG ANTI ICE switch - ON (after engine start)
2. PITOT ANTI ICE switch - ON (after taxi but prior to takeoff)
If an INLET ICE caution appears prior to takeoff -
1. Do not takeoff. Return to the line and have the engines inspected for possible FOD.
20.1.2 Inflight.
If icing is anticipated or encountered -
1. Enter the clouds at the last possible moment. If on top, descend rapidly.
2. ENG ANTI ICE switch ± ON
3. PITOT ANTI ICE switch ± ON
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If no ice is visible on the LEFs -
4. Airspeed - Increase until INLET TEMP is at least +5°C (+10°C preferred) on ENG format (if
possible).
5. Climb or descend out of icing danger zone (figure 20-1).
Monitor INLET TEMP and Mach. If time and fuel permit, climb to a safe altitude. Altitudes
above about 25,000 feet or ambient temperatures below -30°C generally prevent ice formation
since the water droplets are frozen and do not adhere. Descend only if sure that ambient
temperature is well above freezing at a safe altitude below.
When clear of icing conditions -
6. ENG ANTI ICE switch - OFF
If ice is visible on the LEFs -
4. Throttles - Reduce below 80% N2 rpm (if possible). Avoid throttle transients above 90% N2 rpm.
5. Airspeed - Maintain above 250 KCAS.
6. AOA - Maintain less than 6° (if possible) to prevent ice accumulation on underside of LEX.
7. Avoid abrupt maneuvers and bank angles over 20°.
8. Descend rapidly below the freezing level.
Figure 20-1. Icing Danger Zone
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For landing -
9. WINDSHIELD switch - ANTI ICE or RAIN (as required)
The ANTI-ICE position should be used as required to clear the windshield of ice and/or visible
moisture.
Do not operate the windshield anti-ice/rain removal system on a dry
windshield. If a WDSHLD HOT caution appears, place the WINDSHIELD
switch to OFF immediately to prevent heat damage to the
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