.
With Moderate Or Greater Turbulence (reported or with radar indications) ............................................ MEDIUM
.
With Temperature/Dew Point Spread Between 30 and 50 degrees Fahrenheit ..................................................... MEDIUM
.
Onboard Windshear Detection System Alert (reported or observed) ....................................................................... HIGH
Pirep Of Airspeed Loss Or Gain
.
20 Knots Or Greater .......................................................................... HIGH
.
Less Than 20 Knots .................................................................... MEDIUM LLWAS Alert/Wind Velocity Change
.
20 Knots or Greater ........................................................................... HIGH
.
Less Than 20 Knots .................................................................... MEDIUM
.
Forecast Of Convective Weather........................................................LOW
Note: These guidelines apply to operations in the vicinity (within 3 miles of the point of takeoff or landing along the intended flight path below 1,000 feet AGL). The clues should be considered cumulative; and if more than one is observed, the probability is increased. The hazard increases with proximity to the convective weather. Weather assessments should be made continuously.
Takeoff Precautions
Airports Without Terminal Doppler Weather Radar:
If the preceding conditions exist and PIREPS indicate a windshear in excess of 15 knots with increasing intensity, delay departure 30 minutes.
If the preceding conditions exist and PIREPS indicate a windshear of less than 15 knots with diminishing intensity, delay departure 15 minutes.
Airports With Terminal Doppler Weather Radar:
A Microburst Alert or Windshear Alert will be issued by the tower in conjunction with a clearance to a specific runway. If the clearance does not contain an alert, the flight crew may assume that no alert exists at the present time.
If a Windshear Alert accompanied by a reported gain of airspeed is issued, the crew may take off but be alert for sudden airspeed increase. If airborne, the pilot should adjust pitch attitude smoothly to maintain desired airspeed but should not chase large rapid airspeed fluctuations.
If a Windshear Alert accompanied by a reported loss of airspeed, or a Microburst Alert is received, a takeoff should not be attempted. If either alert is received during takeoff prior to 100 knots, the takeoff should be aborted. If either alert is received after 100 knots, the takeoff may be aborted or continued at Captain’s discretion after considering runway available, gross weight, and related meteorological conditions.
If after careful consideration, the decision is made to take off:
1.
Select the longest suitable runway that avoids suspected areas of windshear. The choice of a suitable runway involves consideration of exposure to obstacles after liftoff and crosswind and tailwind limitations.
2.
Normal takeoff thrust should be used. (Flex takeoff is prohibited.)
3.
The flight director and autothrottles will be turned off and not used.
4.
Takeoff flaps should be at one of the recommended settings of 11°, 15°, or 4°. Flaps 4° is appropriate on long runways where the greatest concern
is climb performance after takeoff. Flaps 15° is appropriate on short runways where the greatest concern is takeoff roll and initial liftoff. Flaps 11° is recommended in most situations as it covers a larger range of conditions and provides autoslat protection.
5.
Use increased VR speed if available. The delayed rotation speed must not exceed either the runway limit VR speed or a 20 knot increase.
.
Determine the V1, VR, and V2 speed for the actual aircraft gross weight and flap setting. Set airspeed bugs to these values in the normal manner.
.
Determine the runway limit gross weight for the selected runway by consulting the runway analysis in the flight departure papers. Determine VR for the runway limit gross weight. If not listed on the runway analysis, consult Section 5, V-Speeds for Takeoff-Manual Calculation to determine runway limit VR.
.
Use the higher VR speed (up to 20 knots in excess of actual gross weight VR) for takeoff. Airspeed bugs should not be reset to the higher speeds.
.
Rotate to normal initial climb attitude at the increased VR and maintain this attitude. This technique produces a higher initial climb speed which slowly bleeds off to the normal climb speed.
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