Windshear and Microbursts
Windshear and microbursts are dangerous weather phenomena that can have severe effects on aircraft performance, especially during takeoff and landing. Pilots must understand how to recognize, avoid, and respond to these hazards to ensure flight safety.
1. What is Windshear?
Windshear is a sudden and significant change in wind speed and/or direction over a short distance. It can occur at any altitude but is particularly hazardous when experienced at low altitudes during takeoff or landing.
Types of Windshear
- Horizontal Windshear: A rapid change in wind direction or speed along the horizontal plane. Common near weather fronts or jet streams.
- Vertical Windshear: A sudden change in wind speed or direction along the vertical axis. Often found near thunderstorms or temperature inversions.
Causes of Windshear
- Thunderstorms: Strong downdrafts and gust fronts can create severe windshear.
- Temperature Inversions: When warm air sits over cooler air, windshear can occur at the boundary layer.
- Frontal Systems: Rapidly moving cold fronts can cause windshear along their leading edges.
- Mountain Waves: Windshear can occur in the turbulent airflow downwind of mountain ranges.
2. What is a Microburst?
A microburst is a localized, intense downdraft that spreads out upon reaching the ground, creating strong winds in all directions. Microbursts are a specific type of windshear and are extremely dangerous to aircraft.
Characteristics of Microbursts
- Small Scale: Typically less than 2.5 miles in diameter.
- Short Duration: Usually lasts 5–15 minutes.
- Intense Winds: Can produce wind speeds exceeding 100 knots.
Types of Microbursts
- Dry Microbursts: Occur in dry conditions with little precipitation. They are harder to detect visually.
- Wet Microbursts: Associated with heavy rain and thunderstorms. They are more visible due to rain shafts and virga (rain that evaporates before reaching the ground).
Warning: Microbursts can cause rapid changes in airspeed and altitude, potentially leading to loss of control or terrain impact, especially during takeoff or landing.
3. Effects on Aircraft
Windshear and microbursts can have severe effects on aircraft performance. These include:
- Loss of Airspeed: A sudden tailwind can cause a rapid drop in indicated airspeed, reducing lift.
- Altitude Loss: Strong downdrafts can push the aircraft toward the ground, especially during low-altitude operations.
- Increased Workload: Pilots must quickly recognize and respond to changing conditions, increasing the risk of errors.
4. Recognizing Windshear and Microbursts
While windshear and microbursts are not always visible, there are signs that pilots can look for:
Visual Indicators
- Virga (rain that evaporates before reaching the ground).
- Dust or debris blowing in all directions near the ground.
- Rapidly changing cloud formations or rain shafts near thunderstorms.
Weather Conditions
- Thunderstorms or cumulonimbus clouds in the vicinity.
- Frontal boundaries or rapidly changing temperatures.
- Hot, dry conditions that may lead to dry microbursts.
Onboard Systems
- Ground Proximity Warning System (GPWS): Provides warnings of potential terrain impact due to sudden altitude loss.
- Windshear Detection Systems: Many modern aircraft are equipped with systems that alert pilots to windshear events.
5. Avoidance and Recovery Techniques
The best defense against windshear and microbursts is avoidance. However, if encountered, pilots must know how to recover safely.
Avoidance
- Preflight Planning: Check weather reports (METARs, TAFs, and SIGMETs) for thunderstorms, frontal activity, or windshear advisories.
- Monitor ATIS or AWOS: Listen for windshear alerts at your departure or destination airport.
- Visual Scanning: Avoid areas near thunderstorms, virga, or blowing dust.
- Delay or Divert: If windshear or microbursts are reported, consider delaying departure or diverting to another airport.
Recovery
- Maintain Aircraft Control: Focus on flying the aircraft and maintaining a safe attitude. Use full power if necessary.
- Pitch for Best Climb Rate: Follow your aircraft’s windshear escape procedures, typically involving a pitch to best climb while avoiding stall warnings.
- Do Not Change Configuration: Avoid retracting or extending flaps and landing gear during recovery to prevent further performance degradation.
- Communicate with ATC: Report windshear or microburst encounters to assist other pilots and ensure safe operations.
Tip: Practice windshear recovery procedures with a flight instructor to build confidence in recognizing and responding to these conditions.
6. Reporting Windshear and Microbursts
Pilots should report any encounters with windshear or microbursts to ATC or FSS. Include details such as:
- Location (e.g., airport, runway, or enroute position).
- Altitude and phase of flight (e.g., takeoff, approach).
- Intensity and effects on the aircraft (e.g., airspeed loss).
7. Conclusion
Windshear and microbursts are among the most dangerous weather phenomena for aviation, particularly during takeoff and landing. Understanding their causes, recognizing warning signs, and practicing avoidance and recovery techniques are critical for flight safety. Always prioritize safety by planning your flight carefully and using available weather resources to avoid hazardous conditions.