GROUND HANDLING EQUUIPMENT

 

DELAYED FLIGHT´S PASSENGER AT THE DESK

 

COURSE HEADING TRACK

 

LIGHT SIGNALS FROM ATC TOWER TO ACFT

 

WIND SHEAR

his business aviation blog continues from our article last week, entitled "Wind Shear and Its Impact on Flight Operations: Part 1 – Definitions."

For business aircraft operators, wind shear can have significant impact during takeoff/landing due to its effect on control of the aircraft. Wind shear can be the sole or one of the contributing causes of many aircraft accidents. Low-level/surface-level wind shear is caused mostly by thunderstorm and frontal system activity, while, at higher flight levels, wind shear is usually related to jet stream and frontal activity.

The following is an overview of what you need to know:

1. Wind shear on a flight plan is not a turbulence value

There’s often confusion regarding wind shear and shear values as they relate to flight turbulence. This is due to misconceptions about the relationship between wind shear value and turbulence. A wind shear number is simply a numerical value of differences in wind speeds between flight levels. This value does not necessarily predict turbulence. To determine potential for turbulence associated with wind shear, it’s best to speak with a 3rd-party provider, aviation meteorologist, or flight dispatcher. They’ll look at wind shear values – along with satellite imagery, weather models, and other data – to help determine if potential for turbulence exists. There are different types of turbulence, and the impact of this turbulence depends on your type of aircraft. Maximum takeoff weight, wingspan, and wing loading all impact aircraft performance in relation to wind shear and susceptibility to turbulence. The military, for example, usually calculates predicted turbulence based on the type of aircraft.

2. Relevance of wind shear values

Wind shear values help determine the possibility of turbulence being experienced in flight, but these values are not true indicators of potential of turbulence. It’s best not to rely on wind shear values alone in terms of predicting turbulence. Wind shear should, instead, be used as an indicator to look further into the potential for flight turbulence.

3. Wind shear scales

There are no pre-determined scales used for wind shear, but each operator will typically have his or her own comfort zone. For example, an operator may stipulate that any wind shear value over five requires the crew to be notified and obtain an in-depth weather briefing based on their route and time of flight. There are times of year and regions of the world where wind shear values tend to run particularly high. A good example is traveling over the Newfoundland area during winter and in the presence of strong jet stream activity. Here, wind shear values of eight-10 can be the norm.

4. Wind shear and aircraft type

The main reason there’s no pre-determined scale for wind shear is that wind shear does not necessarily correlate to flight turbulence. The reason for this is because turbulence experienced on a particular trip depends so much on the type of aircraft.

5. Clear air turbulence

Clear Air Turbulence (CAT) is usually based on jet stream activity. Calculation of wind shear values can help try to identify CAT. It’s important to note, though, that, while wind shear may cause CAT, wind shear and CAT are not the same.

6. Obtaining forecast wind data

Forecast wind data is normally published every six hours and can be found from reliable sources such as the U.S. National Weather Service or the UK MET. The closer the forecast data is to the actual time of flight, the more accurate the data will be in terms of predicted conditions you’ll encounter. Be mindful that forecast wind model data can change greatly between the times it’s published. For flight planning purposes, it’s suggested to run flight plans based on historical winds, well in advance, followed by test flight plans a day or two ahead of the estimated time of departure. Particularly for longer (seven-hour plus) flights, the crew should obtain latest wind data as close as possible to time of departure.

Conclusion

It’s important to understand how wind shear may impact your flight. Best practice is to obtain a weather brief day of flight and to talk with a meteorologist to better understand potential wind shear-related issues. Keep in mind that wind shear is only an indicator of flight turbulence and does not necessarily mean that you’ll experience actual flight turbulence. Type of aircraft will be a key consideration in turbulence experiences from shear.

LEVEL OFF/LEVEL BUST/VIDEO

LEVEL OFF/LEVEL BUST

SNOW AND BLOWING SNOW HAZARDS

Hazards to flight

Snow and blowing snow can greatly affect aircraft on the ground, as well as during ascent and descent. When visibility is significantly reduced, as a result of snow activity, aircraft acceptance rates are often reduced. This causes operational delays, and at times aircraft may need to divert to alternate airfields. Significant snow accumulation can impact airport operations, and runways may close for plowing. If the rate of snowfall is such that plowing and treatment are not able to keep runways clear, a particular airfield may be forced to close.

4. Snow accumulation

Snow is designated by intensity, based on rate of accumulation and visibility restrictions. Heavy snow is indicated by "+," moderate snow has no designation, and light snow is indicated by "-." As snow is often accompanied by fog, using visibility alone as an intensity descriptor will not necessarily be accurate. Snowfall rates can be calculated, but if snow is melting as it falls or while on the ground, projected snow depth may not be accurate. Pilots need to be aware of these differences.

5. Visibility impact

Snow can greatly affect visibility and has potential to reduce visibility rapidly. This is particularly true in situations in which the intensity of snowfall is increasing. When snow already on the ground is blown about by strong winds, this often leads to rapid reduction in visibility. The following definitions use visibility in determining snow fall intensity. Use these with caution as other factors – such as liquid water content, temperature, and daylight/darkness – also impact visibility.
Below you will see the visibility based on the snow intensity:

• Light Snow: Snow conditions in which visibility is greater than 0.5 mile
• Snow: Snow conditions in which visibility is in a range from 0.25 to 0.5 mile
• Heavy Snow: Snow conditions in which visibility is less than .25 mile

6. Flat-light and white-out conditions

The FAA Safety Library provides a good reference how to avoid white-out situations.

Flat light

An optical illusion also known as "sector or partial white out." It’s not as severe as a "white out," but this condition causes pilots to lose depth-of-field and contrast in vision. Flat-light conditions are usually accompanied by overcast skies, inhibiting any good visual clues. These conditions can occur anywhere in the world but primarily occur in snow-covered areas. Flat light can completely obscure features of terrain, creating inability to distinguish distances and closure rates. As a result of reflected light, this condition can give pilots the illusion of ascending or descending when they’re actually flying level. With good judgment and proper training/planning, however, it’s possible to safely operate aircraft in flat-light conditions.

White out

As defined in meteorological terms, is a condition where a person becomes engulfed in a uniformly white glow. This glow may be a result of being surrounded by blowing snow, dust, sand, mud, or water. In a white-out condition, there are no shadows, no horizon, and no clouds, and all depth-of-field/orientation are lost. White-out situations can be severe in that there are not any visual references to depend on. Flying is not recommended during any white-out situation. Be aware that flat-light conditions can lead to a white-out environment quite rapidly. Both atmospheric conditions are insidious. They sneak up on you as your visual references slowly begin to disappear. White outs, in snow-covered areas, have been the cause of several aviation accidents over recent years.

Self-induced white out

Typically occurs when a helicopter takes off/lands on a snow-covered area. Rotor down-wash picks up particles and re-circulates them through the rotor system. The self-induced white-out effect can vary in intensity, depending upon the amount of light on the surface. This phenomenon can occur even on the sunniest, brightest day with good light contrast. When it happens, there can be a complete loss of visual clues. If the pilot has not prepared for this immediate loss of visibility, the results can be disastrous

View original post: http://www.universalweather.com/blog/2015/01/snow-its-effects-on-aircraft-runways-part-2-dealing-with-snow/#ixzz3PeLWu8di
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