About 500 fatalities and 200 injuries have resulted from wind shear crashes involving at least 26 civil aircraft between 1964 and 1985 in the United States alone. Since 1985, wind shear also has caused numerous near accidents in which aircraft recovered just before ground contact.
In Nigeria Wind shear was first noted on the 24th June, 1956 when an aircraft taking off from Kano airport flew into a thunderstorm microburst with its associated wind shear, crashed with 32 fatalities.
Other aviation accidents in the country linked with wind shear include the Sosoliso crash of December 10, 2005 which had 108 fatalities and the ADC crash on October 29, 2005 with 96 fatalities. The ADC aircraft was attempting to take off from Abuja Airport before the accident.
Wind shear, sometimes referred to as wind shear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere.
Wind shear can be broken down into vertical and horizontal components, with horizontal wind shear seen across fronts and near the coast, and vertical shear typically near the surface, though also at higher levels in the atmosphere near upper level jets and frontal zones aloft.
Wind shear itself is a micro scale meteorological phenomenon occurring over a very small distance, but it can be associated with mesoscale or synoptic scale weather features such as squall lines and cold fronts. It is commonly observed near microbursts and downbursts caused by thunderstorms, fronts, areas of locally higher low level winds referred to as low level jets, near mountains, radiation inversions that occur due to clear skies and calm winds, buildings, wind turbines, and sailboats.
Director-General of Nigeria Meteorological Agency (NIMET), Dr. Anthony Anuforom, who at a press conference answered the question, ‘How can Nigeria’s airspace be secured?’ said that investigations revealed that the air crashes that occurred between 2003 and 2006 were traceable to bad weather and wind shear was also identified.
Anuforom, also said government was concerned about the negative impact of weather on aircraft movement and have stepped up efforts to ensure the establishment/resuscitation of four additional upper air stations at Enugu, Kano, Maiduguri and Lagos.
With the increase in the number of upper air stations from one in Abuja to five, amid plans to establish additional three before the end of the year, safety in the nation’s airspace is assured, he said.
Anuforom said: “Today, we are happy to add one more item to the list of our achievements by reporting that we have successfully installed a Low Level Wind Shear Alert System (LLWAS) at the Murtala Muhammed International Airport (MMIA), Ikeja, Lagos.
“The Site Acceptance Test (SAT) for this system was completed on July 12 and the system is now operational. This achievement is truly historic because this is the first time in the history of aviation in Nigeria that this airport is equipped with this safety-critical equipment.
“You will recall that the aviation industry in Nigeria witnessed its darkest period between 2003 and 2006 when several aircraft accidents occurred resulting in loss of lives. Reports on these unfortunate accidents suggest that wind shear is a contributing factor in some of them.
“Although aviation has been proven to be the safest mode of transport, the spate of air crashes at that time created unnecessary panic and had a negative impact on the confidence of Nigerians in air travel. It, therefore, became necessary for the Federal Government, through the Ministry of Aviation and its parastatals to take steps to reassure Nigerians that safety and security in our airspace are still paramount in its programmes and its parastatals in this regard.”
Wind shear has a significant effect during take-off and landing of aircraft due to their effects on control of the aircraft, and has been a significant cause of aircraft accidents involving large loss of life within the United States.
It is against all this that Nigeria, in a bid to safeguard lives on the air began installation of Low Level Wind shear Alert System (LLWAS) in all its international airports and has completed installation for the ones in Abuja and Lagos respectively.
The LLWAS project executed by the Nigerian Meteorological agency (NIMET) is a major requirement for the qualification of the International Civil Aviation Organisation (ICAO) Audit.
According to flight statistics, in the Murtala Muhammed Airport, an average of 240 aircraft land and take off each day ferrying no fewer than 17,000 passengers and the installation of LLWAS has further enhanced the safety level of this airport.
According to research carried out by NASA, Wind shear poses the greatest danger to aircraft during takeoff and landing, when the plane is close to the ground and has little time or room to manoeuvre.
During landing, the pilot has already reduced engine power and may not have time to increase speed enough to escape the downdraft. During takeoff, an aircraft is near stall speed and thus is very vulnerable to wind shear.
NASA investigations show that pilots need 10 to 40 seconds of warning to avoid wind shear. Fewer than 10 seconds is not enough time to react, while more than 40 seconds is too long, atmospheric conditions can change in that time.
And because of this, three systems are being flight-tested to give advance warning of windshear:
Microwave radar: Sends a microwave radar signal ahead of the aircraft to seek raindrops and other moisture particles. The returning signal represents the motion of those raindrops and moisture particles, and this is translated into wind speed. Microwave radar works better than other systems in rain but less well in dry conditions. Because it points toward the ground as the plane lands, it picks up interfering ground returns, or “clutter.”
However, researchers are progressing in efforts to eliminate this interference. The radar transmitter is made by Rockwell International’s Collins Air Transport division in Cedar Rapids, Iowa. NASA’s Langley Research Center has developed the research signal-processing algorithms and hardware for the windshear application.
Doppler LIDAR: A laser system called Doppler LIDAR (light detecting and ranging) reflects energy from “aerosols” (minute particles) instead of raindrops. This system can avoid picking up ground clutter (moving cars, etc.) and thus has fewer interfering signals. However, it does not work as well in heavy rain.
Infrared: Uses an infrared detector to measure temperature changes ahead of the airplane. The system monitors the thermal signatures of carbon dioxide to look for cool columns of air, which can be a characteristic of microbursts. This system is less costly and not as complex as others, but does not directly measure wind speeds.
A Low-Level Wind-Shear Alert System has been installed on the ground at more than 100 U.S. airports and two in Nigeria’s 22 airports. Wind speed and directional sensors report to a central computer, and controllers can alert pilots in the event wind shear is detected. But the systems cannot predict when wind shears are approaching.