Microbursts

Microbursts

Definition

Microbursts are small scale, very intense downdrafts which descend to the surface and upon contact with the surface, diverge outwards in all directions.

Images of Microbursts

tsmicro.jpg microburst.jpg
Picture embedded from PJKelly on 26 Sep 09 Picture embedded from Ingraham on 26 Sep 09

Characteristics

Characteristics of Microbursts [1]
Size Covers an area less than 2.5 miles in diameter
Intensity Downdrafts are 40 kts, Horizontal winds between 45 - 100 knots
Duration Approximately 15 mins
Visual Signs Often associated with heavy thunderstorms, embedded in heavy rain

Impact to Flight

microburst_e.gif
(Video embedded from YouTube on 27 Sep 2009) Picture embedded from HKWeather on 26 Sep 09

As characterized by the video and image above, microbursts are extremely dangerous for aircraft approaching an airfield to land as they will be flying through 3 different and difficult phases of wind conditions at a critical phase of flight. [2]

Phase 1: Headwind

  • On final approach, the aircraft is on its descent and at a low altitude, it experiences a headwind, causing lift and the aircraft to rise above its descent path.
  • To descent the aircraft back on its descent path, the pilot will decreases speed.

Phase 2: Downdraft

  • As the pilot is descending the aircraft back to its normal descent angle, the aircraft will experience a sudden surge of downdraft.
  • The pilot, now traveling at a lower speed and pushed downwards will attempt to pull the aircraft up.

Phase 3: Tailwind

  • As the pilot attempts to bring the aircraft up, he now experiences a change in wind direction and meets a tailwind.
  • The tailwind decreases lift and makes it difficult to pull the aircraft up; Exacerbated by the low speed, the aircraft is unable to attain sufficient lift and it subsequently crashes due to the close proximity to the ground.

Accidents involving Microbursts

Crash of Delta Flight 191

(Video embedded from YouTube on 26 Sep 2009)

For a more comprehensive overview and analysis of this incident, please refer to Delta Flight 191

Detection and Avoidance

Following a series of crashes with microbursts as the contributing factor, research was conducted with the following recommendations: [1]

  • Pilot Training
    • Incorporated into the training syllabus were means to recognize the characteristics of microbursts
    • Training was done in simulators to deal with microbursts in the proper manner
    • Pilots were also trained to avoid microbursts if possible and divert/ carry out missed approach if necessary
  • Systems
    • Improved weather radar systems were developed and implemented at airports and on aircraft
    • These systems serve to detect microbursts in close proximity to the airport and send out alerts to both pilots and ATC alike

The video below demonstrates the research and tests conducted by NASA in developing a Forward Looking Doppler Radar that has proven beneficial in commercial aircraft in detecting microbursts, providing 40s of warning so that pilots can react accordingly.

(Video embedded from YouTube on 26 Sep 2009)
References
1. NWAS.(2003) National Weather Association's "Thunderstorms and Flying Course.". NWAS.
2. National Weather Service (2009). Thunderstorm Hazards - Damaging Wind. National Weather Service.

Want to know more?

NASA – Making the Skies Safe from Windshear
This page provides details on NASA's Langley Research Center efforts with FAA to develop technology for the airborne detection of microbursts.

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Authors / Editors

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