The Effects of Microburst on Small Aircraft - Research Paper Example

The Effects of Microburst on Small Aircraft Characteristics of microburst A micro burst is a pattern of intense winds that descends from rain clouds, hits the ground, and fans out horizontally (Encyclopedia Britannica, 2009). It is a much localized column of sinking air, which diverges destructively at the surface causing much damage to the surrounding area. Its strong winds can easily knock down fully grown trees down to earth in a few seconds. Microburst is caused due to changes in the atmosphere; two reasons are usually considered the dry extreme condition and wet extreme conditions which cause microburst with heavy rain. In extreme dry conditions when moist convection is just barely possible, cumulus clouds with very high bases form above the surface; below this high-based cloud layer there is a deep, dry adiabatic layer of microburst. In extreme wet conditions a deep, nearly saturated layer with a nearly moist pseudoadiabatic lapse rate forms that is topped by an elevated dry layer which is a cause of microburst. (Fernando Caracena, 2001) In case of dry microburst the rain falls below the cloud base mixes with dry air from where it begins to evaporate and this evaporation process cools the air. The cool air descends and accelerates as it approaches the ground from where it spreads in all directions and the divergence of wind is the sign of a microburst. The wet microburst is accompanied by heavy rainfall at the surface which are warmer then the environment. This downburst pushes the downward acceleration of parcels that cause negative buoyancy which tends to drive dry microburst. (Fred E. Nathanson, J.Patrick Reilly, Marvin N. Cohen, pg.646, 1999) Wind shear is the difference in wind speed and direction over a short distance in the atmosphere. The extent and suddenness of a microburst accompanied with low-level wind shears are a cause of many fatal aircraft crashes; particularly they affect in landing and take-off phases. Duration The microburst is recorded to last no more then 15 minutes from the time they strike on the ground. During the first 5 minutes the horizontal wind continues to rise with maximum intensity lasting 2-4 minutes Sometimes microburst are concentrated into a line structure, and under these conditions, activity may continue for as long as an hour. Once microburst activity starts, multiple microbursts in the same general area are not uncommon and should be expected. Hazards to flight The strong, concentrated winds along with rainfall and thunderstorms have caused fatal aircraft accidents. (Downbursts, Fujita, 1985). As the aircraft enters in the way of microburst, it encounters an increased head wind. This head wind lifts the aircraft, the pilots reacts to correct the aircraft approach angle by reducing engine power. The aircraft then passes into the vertically descending microburst core which results in a loss of lift and altitude. Immediately the aircraft crosses into a region of tail winds (the wind which blows in the direction of the object), which reduces the relative airspeed of the aircraft and further decreases lift, causing the aircraft to lose more altitude. Because the aircraft is now flying on reduced power, it is vulnerable to sudden losses of airspeed and altitude. The microburst is often of right scale and intensity to crash an aircraft which is evident by a number of accidents associated with microburst over about a decade. The crew and passengers all become victims to the crash and give their lives. There are a large number of human losses especially if microburst attacks at the time of take-off and landing. Predicting Microburst Microburst has always been a challenge for safety issues regarding the aircraft and small business jets. Its prediction, detection and avoidance are an issue of big concern for aviation authority. The pilots are unable to maintain the balance of strong winds and historically this has plagued the entire civil aircraft types including large commercial transports, regional airliners, business jets, and small personal-owner general aviation vehicles. Between 1970 and 1980s a huge number of fatal accidents occurred in United States and abroad due to wind shear. "About 540 fatalities and numerous injuries resulted from wind-shear crashes involving 27 civil aircraft between 1964 and 1994" (Langevin, 2003). In numerous accidents the aircrafts recovered just before ground contact. On 4th November 2007 the Lear jet 35A departed Campo de Marte Airport (Brazil) on a positioning flight to Rio de Janeiro (Brazil). The takeoff clearance from runway 30 was issued at 14:08, and the flight crew was advised of the strong wind at 2 knots. The airplane was observed to begin the takeoff on runway 30 from the threshold, and after rotation, the tower controller noted the airplane pitched up steeply, and then rolled quickly to the right an estimated 90 degrees. The airplane began a right descending turn, and then rolled left and continued descending. At 14:09, the tower controller advised the flight crew that the turn should be to the left. The flight crew did not respond nor did they declare an emergency and finally it crashed. Weather reported at the airport at 16:00 included a temperature of 22 deg C, dew point 18 deg C, 1012.9 hPa, 4500m visibility in light rain and mist, broken clouds at 1,400 ft. and overcast at 10,000 ft. Many causes have been cited for this incident and other related accidents due to microburst; including flight crews wrong decision to proceed the journey, their failure to recognize the wind shear on their way, their failure to establish and maintain the proper airplane attitude and thrust setting necessary to escape the wind shear, lack of real time adverse weather and wind shear hazard information dissemination form air traffic control. The contributors to microburst related accidents are lack of traffic control procedures which should display weather reports to the pilots, the tower supervisors failure to properly advise the pilot of the reduction in visibility of runway and alerting him of low level wind shear alerts on the way, inadequate remedial actions by the business jet to ensure adherence to standard operating procedures and finally inadequate software logic in the planes wind shear warning system to alert the pilots of microburst coming on its way. The official have reported saying that they saw the "wall of water" (Krause, 1996) approaching. Another report said that it can be possible that all the three control positions ground, local west and final radar failed to issue wind shear warnings after receiving such alerts, it was the controllers responsibility to give the pilot such alerts. The aircraft broke up in pieces and came to rest destroying houses nearby. The safety board has given this incident various faces, and has associated lack of safety measures in the business jet due to which it became victim to the microburst. Lessons learned were To conduct crew briefing before take-off, and Never to under estimate the thunderstorm spells Forecasting activities Due to the resulting microburst pilots have experienced different hazards and it has been important for the authorities to forecast its occurrences. Various pilots have been affected by this trauma. According to ATSB release of 20th September 2002, the pilot of aircraft has reported saying that as the wind shear came near, the aircraft was in its landing phase; it encountered rain and some hail which increased rapidly and as aircraft came nearer to ground the weather deteriorated so the pilot discontinued the approach and applied go around engine thrust. The aircraft went up with much slow speed due to microburst downdraft and the pilot advised the aerodrome controller that aircraft had encountered severe wind shear. The pilot diverted the aircraft to another airport nearby without further damage. This case clearly states that the pilot has to be attentive in case any such situation occurs. The Air traffic control (ATC) advisories have also highlighted the issue and divided the responsibilities of alerting pilots of weather reports during flights. In case the controller signs any danger and alerts the pilot he/she has to remain on an altitude and speed assigned by the ATC board and on the route assigned by ATC, it is also strictly stated that pilots cannot make decisions during the case without ATC clearance. Radars have been set up by the board to avoid dangers. To summarize ATC advisories play a major role in alerting pilots of coming danger and help them in safe landings. In order to avoid dangers caused by microburst few devices have been developed to predict the arrival of microburst. A Doppler radar is usually used which measure the velocity of particles of dust or rain in the direction of the radar antenna but particles moving perpendicular to the radar beam can not be determined. Therefore, microburst downdrafts cannot be measured by Doppler radar scanning close to the horizontal plane, which is its normal mode of operation. Doppler radar is an indicator wind shear but not the predictor of its occurrence. U.S. Pat. Lting No. 4,672,305 is a device that measures the ratio of the electric to magneticdangers by field of the discharge of wind and rain particles to determine the distaurst it obnmicrce to the microburst. Most commonly, the reception of the signals generated by lightning are used in predicting wind shear and microburst. A plurality of sensors monitor the different bands of spectrum and then relays the data to a processor which calculates the location of the lightning, the frequency of the discharges, the rate of increase in the frequency of discharge, and the aerial density of the discharges. When the lighting rate and the rate of change of the lightning rate exceed given threshold levels for a given area and there is a peak in the lightning rate, a microburst/wind shear is imminent in that area. Another way is by manual detection which is performed by trained meteorologists who scan through the volumetric radar data for appropriate signatures. Now a days a system have been developed which use computer techniques together with fuzzy logic to detect microburst. The system is implemented in the Java language and is successfully detecting microburst in data from radars near Sydney and Darwin in Australia. The radar functions in the way shown Burst tracks Display MB detector Core detector Shear detector Radar Read data (Stoll, 1991) Microburst effect on small/medium size aircraft Microburst affects both the small and medium size aircraft. Charles Philip of Delta airline has been reported to say "Boy, this is a really strong train shower! We're losing some airspeed...strong tailwind. Wow, look at the tailwind! Come on baby, you can fly! Come on, come on, fly baby, you can make it, come on, come on...oh...aghh" (Lawyer, 2001). (Information was from the flight recorder). The plane then crashed down with full speed and smashed into two four-million-gallons of water tank before coming to a complete stop, this resulted in much causality and many human losses. This showed one of the worst incidents of microburst. What seemed to pilot as just the rain shower was actually a microburst which led him to take a wrong landing decision which resulted in disastrous mishap As far as aerodynamic is concerned the aircraft has a pressure point on its longitudinal axis which is calculated from the contribution to lift from each of the aircraft component, if this pressure point is in front of the centre of gravity the aircraft will be aerodynamically unstable and it will be impossible for the human to control it. As the strong winds come across the aircraft the pressure point lies in front of centre of gravity and the flight unstable and this result in complex situations. The pilot at this time tries to move the aircraft in a position where pressure point moves behind the centre of gravity making it stable. The aircraft are designed in such a way as to reduce drag at a speed and increase the overall performance. Hazards In order to combat with microburst the ATC has formed certain rules and procedures; radars have been setup to detect the wind pressure and direction, as the strong wind is continued with rainfall which results in hazards. The assistance is provided to pilots to avoid bad weather and request them of the new route. The controller's primary function is to provide safe separation between aircraft. It is very important that the request for deviation or radar vector be forwarded to ATC as far in advance as possible. Delay in submitting it may delay or even preclude ATC approval or require that additional restrictions be placed on the clearance. The additional procedures advised for the smaller aircrafts include Limiting take-off and landing if there is any sign of wind shear or microburst In order to improve crew and passenger safety a number of changes have been made in the design and power of aircrafts. The exit doors and routes have been designed in such a way to provide maximum ease and safety at time any such condition occurs. The aircrafts are given alternative routes by the controller if any microburst occurs on the airport destination. The aircraft is loaded with a number of safety features to help cabin members and passengers escape the aircraft with maximum ease and speed. And, The crew members and pilots are given special instructions to deal with such situations. Reporting microburst The concerned authorities have set up rules for aviation known as federal aviation rules (FAR) s which are prescribed by federal aviation authority FAA. A wide variety of activities are regulated by these laws including airplane design, typical airline flights, pilot training activities, hot air ballooning, lighter then aircraft, man-made structure heights, obstruction lighting and marking, and even model rocket launches and model aircraft operations. The rules are designed to promote safe aviation, protecting pilots, passengers and the general public from unnecessary risk. They are also intended to protect the national security of the State. Conclusion Aviation expert have predicted the grown of very light jets (VLJs) in the near future and identified various factors that will change due to VLJs increase. There will be a change in the overall deliveries of both people and goods leading to growth of the air taxi market, secondly dissatisfaction will prevail with other forms of transportation which may lead to higher demand of VLJs; the other affects will be low purchase price and operating costs which again will raise VLJs demand; access to airports of these VLJs will help in boosting number of private and public airports and more smaller airports will be constructed ; training and insurance requirements will require more time and money which could affect negatively to some extent in its growth , production constraints will affect the number of aircraft delivered; lastly economic growth, and expected aircraft retirements will be affected. VLJs might operate shorter flights and travel at lower altitudes than commercial planes and have little effect on capacity which would result in delays and congestions. VLJs likely will be equipped with new technologies and equipment, such as Automatic Dependent Surveillance-Broadcast (ADS-B) that, once deployed by airports nationwide, would help to increase capacity by providing position, intent, velocity, and other information between aircraft and ground systems to manage air traffic. They could segregate the air traffic if they traveled in same airspace. The FAA is taking steps to facilitate a better coordination between VLJs and the ground controllers taking help of latest technologies and procedure to provide information between VLJ and controller as part of FAA's modernization efforts. The FAA officials believe that there is a need to change existing aviation standards and regulations to successfully integrate VLJs. "The two very light jet models currently operating; the Eclipse 500 and the Cessna Citation Mustang; were required to pass these certification and airworthiness standards, including special conditions" ( Fleming, 2007). FAA has established standards for the certification of pilots, instructors, maintenance technicians and repair stations. These standards are based on the complexity and classification of the aircraft and type of operation. Work cited 1. Charles A. Doswell, Fernando Caracena, Ronald L. Holle, Microburst, A handbook for visual identification, 14th June 2001. 2. Charles F. Spence, AIM/FAR 2008, Airport operations, Mc Graw Hills, 2008. 3. C. O. Hayenga and J. W. Warwick, Two-Dimensional Interferometric Positions of UHF Lightning Sources, Journal of Geophysical Research, vol. 86, No. C8, pp. 7451-7462, 1981. 4. David T. Lawyer, Flying safety, Microburst: An aviator's worst nightmare, December 2001. 5. E. R. Williams, A lightning precursor to microburst in thunderstorm, Trans. Amer. Geophysics. Union, pg. 1227, 3rd November 1987. 6. E. W. Coleman, LSZ-850 Lightning Sensor System, Proceedings of the 1988 International Aerospace and Ground Conference on Lightning and Static Electricity, Oklahoma City, Apr. 19-22, 1989, NOAA special report, pp. 434-438 7. F. Carcena and J.A. Flueck, Classifying and forecasting microburst activity in the Denver area, J. Aircraft, 25, 525-530, 1988. 8. Fred E. Nathanson, J. Patrick Reilly, Marvin N. Cohen, Radar design principles: signal processing and the environment, Hybrid processor, meteorological radar and system performance analysis, 2nd edition, Sci Tech publishers, 1999. 9. Fujita T. Theodore, The downburst, Microburst and macro burst, SMRP University of Chicago, 1985. 10. Gail S. Langevin, Wind shear, NASA Officials, October 17, 2003 http://oea.larc.nasa.gov/PAIS/Concept2Reality/wind_shear.html 11. J. M. McClellan, Storm busters, flying, pp. 64-68, Mar. 1987. 12. Matt Thurber, Aviation maintenance, Access intelligence, 23rd August 2008. 13. M. Weber and E. R. Williams, Rapid Update Doppler Radar and Electrical Measurements of a Microburst Producing Thunderstorm, Abstract A41B-08 EOS Transactions Amer. Geophysics Union, p. 1227, Nov. 3, 1987. 14. R. Rotunno and J. B. Klemp, The influence of the shear-induced pressure gradient on thunderstorm motion, Monday Wea. Review, 110, 136-151, 1982. 15. Robert A. Houze, Cloud dynamics, downbursts, Academic press California, 1993. 16. Shari Stamford Krause, Aircraft safety: accident investigation, analysis and application, MC Graw Hills, 1996. 17. Stoll S. A., Microburst detection by the Low-Level Wind Shear Alert System, Weather, 46, 334-347, 1991. 18. Susan Fleming, United States government accountability office: Report to congressional requesters, Very light jets; several factors could influence their effect on the national airspace, August 2007. http://www.gao.gov/new.items/d071001.pdf 19. W. Warwick, C. O. Hayenga and J. W. Brosnahan, Interferometric Directions of Lightning Sources at 34 MHz, Journal of Geophysical Research, vol. 84, No. C5, pp. 2457-2467, 1979. 20. Australian government: Australian transport safety bureau, Media release: ATSB releases report on microburst wind shear serious incident, 20th September 2002. http://www.atsb.gov.au/newsroom/2002/release/2002_10.aspx Read More