What are downdraft wind shears??

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There are many types of winds, but today we will talk about some very dangerous ones that affect aviation on a daily basis. What are downdraft wind shears?? Photo by flugsnug via YouTube.

Given the recent accident without fatalities of Aeroméxico in Durango, where an embraer 190 went off the track and finished a few 300 meters from the head, many speculations about what could have happened has been around the internet.

with this post, we do not want to draw conclusions and much less anticipate the results or causes of the accident, that only the final report and the country's authorities can give, but before the appearance in the media about the terms wind shear or shear, we find it prudent to inform the community about its meaning and what it implies for aviation.

post writer by: Captain Rudolph Star
FAA Commercial Pilot
Twitter: @rodo_estrella

In simple terms, wind shear is a condition where the wind within a short distance abruptly changes speed and direction, be it horizontal or vertical, shear is generally associated with a variety of meteorological conditions such as temperature inversions, frontal systems, strong surface winds and the most violent: thunderstorms and heavy rain.

Of the shear classes in terms of severity, studies show that changes in wind speed range from 15 knots and currents with speeds greater than 500 feet per minute.

Figure 1 (FAA source)

The production of shear in the event of the electrical storm (figure 1) occurs during the dissipation stage of the same characterized by heavy rains that create descending currents of air, these areas usually have dimensions between 1 a 5 miles in diameter.

the micro burst

Within what is the shear or windshear, we found the phenomenon of the microburst, which is one of the meteorological elements that affect the aeronautical operation in a more significant way, these are powerful concentrated downdrafts of air, They usually cover small areas of about 3.000 feet in diameter.

Its impact against the ground generates rings of lateral vortices of areas up to 12.000 feet in diameter and can be as high as 2.000 feet on the ground. These vortices can generate eddy updrafts that can cause lateral stability problems in aircraft..

Multiple microburst areas can be present within the same associated weather phenomenon and their dissipation period is usually around 10 a 20 minutes after contact with the ground.

Figure 2 (fuente: FAA)

Problems in the aeronautical operation

Microbursts are particularly dangerous in the takeoff and landing phases because their most adverse effect comes from contact with the surface..

Shear and its effects are difficult to predict and are not easily visible to the naked eye, so it is often difficult to avoid., however, techniques have been developed for handling them in case of encountering them for pilots and early detection systems in flight in aircraft with advanced systems..

further, some aerodromes have wind shear reporting systems to warn flights about wind shear, However, the system is not implemented in all aerodromes and many times the wind shear reports come from aircraft that encounter the phenomenon in flight.

Pilots are regularly trained and evaluated in wind shear management and this training consists of recognizing it based on the performance and behavior of the aircraft when encountering this phenomenon.. Thus, apply procedures to recover control of aircraft that are affected by wind shear,

Regrettably, the variation in intensity and the conditions in which they can occur mean that any detection and/or management procedure is not completely effective, so it will always be a latent danger in any air operation.

Figure 3 (fuente: FAA)

The regulatory agencies of the aeronautical system around the world simply recommend not to operate at aerodromes where windshear is reported. (although its existence cannot always be known) and the industry directs its efforts in technology for the effective detection of shear both on land, as in instrumentation inside aircraft.

Finally, airlines and pilot training programs focus on training crews to recognize and most effectively deal with this phenomenon.

Air accidents by wind shear

In the history of aviation, 113 accidents have been attributed to meteorological problems, among them, various due to wind shear or other extreme wind conditions.

This is a part of those accidents, being one of the most representative, that of Delta Air Lines in 1985 (ASN Source):

Date	Airplane	Registration	Airline	fatalities
31-May-84	Boeing 727-222	N7640U	United Airlines	0
02-Aug-85	Lockheed L-1011 TriStar 1	N726DA	Delta Air Lines	134+ 1
14-Sep-86	BN-2A Trislander Mk.III-2	G-BDTP	legend	1
04-Apr-87	DC-9-32	PK-GNQ	Garuda	23
05-Aug-89	Learjet 25D	PT-KYR	Locadora Belauto Ltd.	4
03-Sep-89	Ilyushin Il-62M	CU-T1281	Cuban	126+ 24
19-Jan-90	Gulfstream American G-1159 Gulfstre	N46TE	Eastman Kodak	7
21-Dec-92	DC-10-30CF	PH-MBN	Martinair Holland	56
14-Sep-93	Airbus A320-211	D-AIPN	Lufthansa	2
02-Jul-94	DC-9-31	N954VJ	USAir	37
23-Apr-95	DHC-6 Twin Otter 300	5N-AJQ	Bristow Helicopters	1
10-Jun-97	Harbin Yunshuji Y-12 II	JU-1020	mine	7
18-Mar-99	Douglas DC-3C	HK-337	ALIANSA Colombia	8
22-Jun-00	Xian Yunshuji Y-7-100C	B-3479	Wuhan Airlines	42+ 7
10-Dec-05	DC-9-32	5N-BFD	Sosoliso Airlines	108
29-Oct-06	Boeing 737-2B7	5N-BFK	ADC Airlines	96
21-May-08	Beech T-1A Jayhawk	93-0633	USAF	0
04-Apr-11	Canadair CRJ-100ER	4L-GAE	Georgian Airways, op.for UN	32
02-Sep-11	CASA C-212 Aviocar 300DF	966	Chilean AF	21
20-Apr-12	Boeing 737-236A	AP-BKC	Bhoja Airlines	127
01-Jul-12	Lockheed C-130H Hercules	93-1458	USAF	4
06-Mar-18	Antonov An-26	RF-92955/52	Russian AF	39

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