Judging The Wind

Patrick AydFAA Safety Team Representative

NWS Bismarck Meteorologist

Judging The WindJudging The Wind

Why Wind?2003-2007 Part 91 Weather Related Accident Citations

Why Wind?2003-2007 Part 91 Wind Accident Breakdown

Why Wind?2003-2007 Part 91 Phase of Flight for Wind Accidents

Why Wind?• Number one weather related aircraft accident factor.

• Leading causes of wind related accidents: Gusts, crosswinds and tailwinds.

• Most likely phase of flight: Landing

• Wind was also a leading factor amongst weather related accidents for part 121 and 135 operations.

While some amount of crosswinds and turbulence are un-avoidable and part of day to day flying, the majority of wind related accidents are avoidable:

1.Obtain a proper weather briefing to recognize wind related hazards.2.Know your aircraft’s AND your own personal wind thresholds.

3.Remain proficient. If you have not flown in winds in a while, seek some time with an instructor.

Sources of Wind Information

TAF and The Tactical Decision Aid

• The Tactical Decision Aid (TDA) is a graphical, color coded representation of the TAF.

• Available on the TDA is the option to calculate the crosswind, headwind and tailwind components for all runways at a particular TAF site.

• NWS Bismarck Aviation Webpage: www.weather.gov/bis/aviation_briefing

AIRMET Tango

• Moderate or greater turbulence (referenced to a single engine aircraft)• Sustained surface winds of 30 kts or more• Low Level Wind Shear (LLWS)• Updated every 3 hours, with 3 hourly forecasts for the next 12 hours (Quick snapshot

of possible high wind areas and LLWS/turbulence potential along a route).

Favored Areas For Strong Wind• Strongest winds in ND: behind a cold

front on the backside of a deep low pressure system.

• A tight pressure gradient between a strong surface high and low (isobars are close together).

• What to think about: • Am I crossing any fronts during

my route (fuel considerations)?

• Is my destination airport near a front (possible wind shifts)?

• Will thunderstorms be in the area (outflow boundaries)?

Single Runway Airports• While runway configuration is designed to take

advantage of the most common prevailing winds, high impact weather systems often yield non-climatological wind directions.

• This presents the potential for significant crosswinds, especially at single runway airports.

• Check surrounding TAFs, surface wind prog charts and the latest observations to determine the wind direction and strength at your destination, arrival and alternate airfields prior to and during flight.

• For single runway airports where cross winds are likely, having an alternate airport with a more preferable runway configuration is essential.

Windspeed from Windsocks• Federal regulations dictate

that a fully extended windsock indicates a wind speed of 15 kts

• If the wind sock is flapping, gusty/fluctuating winds are occurring which may lead to airspeed and flight control effectiveness changes on final to flare.

• A flapping wind sock may also be a result of mechanical turbulence.

Mechanical Turbulence• Gain knowledge from local airport personnel or other

pilots regarding known mechanical turbulence hazards resulting from winds interacting with terrain and airport structures, especially when flying into new and unfamiliar airports.

• Overfly the field, making note of the wind direction and possible structures, trees etc. that may cause eddies to form in the final approach to touchdown zone.

• During run-up, check the lift-off to initial climb zone for possible hazards that may generate low level turbulence

• Knowledge is power!! Anticipating and planning for possible turbulence and airspeed fluctuations on short final or take-off allows for these operations to be safely conducted in windy conditions.

Mechanical Turbulence• Crop dusters are especially susceptible

to mechanical turbulence when operating near tree rows and/or rolling terrain.

• Before beginning operations, make note of the wind direction from the crops in the field, trees etc.

• What portions of the areal application site are most likely to generate mechanical turbulence?

• Are any eddies clearly evident (i.e dust devils in the field, swirling leaves/grasses)?

• Use an application pattern that mitigates the risk

Mechanical Turbulence• Assuming a

headwind takeoff, low level eddies from the terrain and trees upwind may result in mechanical turbulence being experienced shortly after takeoff.

• Identify the hazard! Be prepared!!

Wind Correction On Takeoff• Hold aileron control

into the crosswind. This generates a downward force on the upwind wing, countering the tendency for the crosswind to raise the wing.

• Use rudder to maintain centerline.

• As airspeed increases and flight controls become more effective, control pressure should be relaxed.

Stay Updated• If flying into a towered airport, ask

for wind checks from tower personnel while in the traffic pattern.

• If flying into a non-towered airport, take advantage of the co-pilot or a passenger to monitor ASOS/AWOS on the secondary radio and provide updates to you.

• From this information, are the winds fluctuating or steady? Is a landing on the intended runway still feasible? Should I consider carrying more power and using less flaps?

When to Go Around and/or Divert• If using a side slip to counter cross

winds on approach to landing, if required bank is such that full opposite rudder cannot prevent a turn, the winds are too strong to make a safe landing.

• Initiate an immediate go around.

• Either make an approach on a runway that is more favorably aligned with the winds, or divert to an alternate airfield.

• ANTICIPATE!!! If at near full rudder deflection while on final approach, consider a go around before reaching the runway. Decreasing airspeed during the flare will reduce the effectiveness of the control surfaces, and the control inputs required to maintain centerline make exceed the ability of the aircraft.

Final Approach Wind Gust Correction• FAA approved correction to final approach airspeed is to add ½

of the gust factor to the normal final approach airspeed

Example:

Sustained windspeed: 25 kts Gust: 35kts

Gust – Windspeed = Gust Factor

35 kts – 25 kts = 10 kts

Thus, increase final approach airspeed by 5 kts

Final Approach – GPS Groundspeed

• Growing in popularity is the use of GPS ground speed to anticipate wind shear on final approach

• Using this procedure, the pilot matches the GPS groundspeed to the normal final approach airspeed

Example:

Normal approach airspeed: 80 kts Headwind: 30 ktsGroundspeed: 50 kts

If GPS groundspeed was matched to normal approach airspeed, GPS ground speed would be 80 kts and airspeed would be 110 kts given 30 kt headwind component before wind shear encounter.

Final Approach – GPS Groundspeed

Example continued:

Normal approach airspeed: 80 kts Headwind: 30 ktsGroundspeed: 50 kts

If GPS ground speed was matched to normal approach airspeed, GPS ground speed would be 80 kts and airspeed would be 110 kts given 30 kt headwind component before wind shear encounter.

Now assume the worst case scenario of a maximum wind shear resulting in a loss of 30 kts (all headwind is lost). Groundspeed would remain at 80 kts due to inertia of the aircraft overcoming the effects of the sudden wind shear. Minimum airspeed with this shear encounter would also be 80 kts, which is the indicated airspeed that is normally used on final.

Final Approach – GPS Groundspeed• Touchdown ground speed determines landing roll distance,

not airspeed!

• Thus, carrying excess airspeed when crossing the runway threshold will not increase the landing distance required.

• However, carrying extra airspeed results in a lower nose attitude than normal when crossing the threshold. This can be countered in two ways:

1. Enter a prolonged flare to dissipate the excess airspeed

2. Gently roll mains on runways and be aware that the nose gear may touch down at nearly the same time. Hold back pressure on the control wheel and break gently during initial rollout to prevent wheel-barrowing.

Don’t Let Up!!• While the airplane is decelerating

during the after landing roll, more and more aileron is applied to keep the upwind wing from rising. Since the airplane is slowing down, there is less airflow around the ailerons and they become less effective.

• At the same time, the relative wind is becoming more of a crosswind and exerting a greater lifting force on the upwind wing. When the airplane is coming to a stop, the aileron control must be held fully toward the wind.

Personal Thresholds• While your aircraft have maximum demonstrated

crosswind and tailwind components, they may not be the same as the pilot.

• What are your personal crosswind thresholds (what has or would make you feel uncomfortable)? Has your instructor suggested any limits?

• When was the last time you operated in strong winds or made takeoffs and landings with significant crosswind components?

• NEVER be afraid to get a refresher with an instructor.

• Don’t be blown around, stay on the ground!!!