Сase Study Wind Shear

Deadly Downdrafts Aaron C. Bouchard Liberty University Abstract On August 2, 1985 Delta Airlines Flight 191 travelling from Fort Lauderdale, Florida to Los Angeles made an en route stop at Dallas Fort Worth when it encountered wind shear on final causing it to crash into the ground and bursting into flame. This accident killed 134 passengers and crewmembers, as well as the driver of a passing car. This case study will analyze how microbursts and extreme wind shear led to the demise of this flight.

Using National Transportation Safety Board (NTSB) airline accident report 86/05 it reveals that the events leading up to the accident and the actions of the crew members were inadequate to correct for the developing weather.

After analyzing the accident report, it was apparent that the Federal Aviation Administration and meteorologists around the country were incorrect in dismissing previous weather theories and needed to implement more tools to observe and monitor critical weather phenomena. At the operational level, flight schools and airline administrators need to ensure aviators are receiving adequate training on the detection of hazardous weather, and the appropriate steps to react to adverse weather conditions to ensure the safety of the crew and passengers.

Deadly Downdrafts Having an adequate understanding of weather phenomena directly affects all aspects of aviation operations. During the 1980s, we did not fully understand some weather phenomena and suffered fatal consequences. One of these fatal occurrences is microbursts, which have been attributed as the cause of multiple aviation incidents. This case study will be analyzing the effects of a microburst on Delta flight 191 at Dallas Fort Worth on August 2, 1985.

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The National Transportation Safety Board (NTSB) Aviation Accident Report (AAR) will form the basis of this study. The first section will identify what a microburst is and analyze the research that has been conducted to help identify and mitigate risks associated with microbursts. Finally, the study will analyze how this incident could have been prevented and how to mitigate further risks associated with this phenomenon. Before every flight, a pilot must conduct a thorough pre-flight evaluation of all aspects related to that flight. One of these aspects is checking the weather forecasts and ensuring the route of flight is clear of any potentially hazardous weather such as thunderstorms. One potentially hazardous aspect of thunderstorms is the immense winds required to create and maintain the storm. The downdrafts that exist during the cumulus stage of the storm can create a microburst. A microburst is a “localized column of sinking air within a thunderstorm” (“What is a Microburst,” para. 1) that can cause extensive damage at the surface.

While the thunderstorm is developing, precipitation such as rain and hail are suspended in the upper portion of the thunderstorm where they cool and sink until the updrafts cannot sustain the weight any longer. This core of precipitation then falls to the surface from the storm, causing extreme downdrafts and damage to anything below it. The immense downdrafts cause wind shear, a fancy name for a rapid change in wind direction and speed which can have fatal consequences during flight especially during critical moments such as takeoff and landing. Prior to 1985, the Federal Aviation Administration (FAA) and most of the aviation world denied the existence of microbursts and therefore impeded the ability of meteorologists to forecast and ultimately warn aviators of their dangers. On August 2, 1985 Delta flight 191 was on a routine flight from Fort Lauderdale, Florida heading to Los Angeles International airport with a brief stop in Dallas Fort Worth for fuel and resupplying.

Prior to departure, the pilots were alerted to a general warning of rain showers and a possibility of thunderstorms over Oklahoma and northern parts of Texas. The NTSB investigation revealed “the NWS terminal forecast for the DFW Airport pertinent to the accident indicated a slight chance of a thunderstorm with a moderate rain shower. The NWS area forecast pertinent to the accident called for isolated thunderstorms with moderate rain showers for northern and eastern portions of Texas.”  They did not contact Delta Airlines weather center to clarify or confirm the weather reports and proceeded with the flight. While en route, they did not experience any weather or notice anything out of the ordinary until they reached Louisiana where the weather was beginning to intensify. The pilots identified this and attempted to adjust course to the north to avoid the worst weather.

As the flight neared the airport, the pilots noticed a large weather cell ahead and requested vectoring to avoid it. Once around the cell the crew noticed rain of Fort Worth and thought they were flying into slight showers, deciding to continue with the approach through the showers. While flight 191 was still on approach two aircraft, including a much smaller leer jet, safely landed despite the rain and before the thunderstorm closed in on them. When flight 191 emerged from the storm cloud, it was reported that the aircraft was at an unsafe attitude and instructed to go around. Shortly after this instruction, the aircraft struck the ground, becoming airborne once more before crashing into an automobile, and back into the ground bursting into flame, killing 135 passengers, crew members and the driver of the unfortunate automobile. Delta flight 191 was not brought down only because of the existence of a thunderstorm or the presence of precipitation but because of the conditions that these elements occurred in and the actions of the crew.

When flying into a microburst an aircraft is met by strong updrafts which then turn into a mixture of up and down drafts before giving way to severe downdrafts. When flying out of the microburst, the pilot is going to encounter a strong tailwind which ultimately robs the aircraft of lift and can force the aircraft into the ground. As flight 191 entered the weather cell they were instructed to slow down by DFW tower personnel, leaving them at the mercy of the weather. The crew then struggled to maintain their approach and fight the downdrafts by increasing engine power and increasing their attitude. Unfortunately, the corrections came too late as the wind shear already disrupted the lift production and forced the plane into the ground before reaching its ultimate demise. As a result of this last devastating accident meteorologists around the country and the world presented substantiating evidence to the FAA and other governing agencies highlighting the processes and ingredients necessary for microburst formation while also identifying solutions to aid the identification, reporting and distribution of this weather information to all aviators and necessary parties.

One of these improvements is the Terminal Doppler Weather Radar (TDWR) which was deployed at strategic airports across the United States and Puerto Rico to allow essential weather information where it is needed most and can provide updates every minute. This allows meteorologists’ and aviators to stay ahead of developing weather cells and assist with risk mitigation at all levels of planning. Another development that was implemented in 2001 is the Integrated Terminal Weather System (ITWS). This system receives imagery and radar reports from a wide variety of weather mapping and reporting systems including low level wind shear indicators, doppler radar and aircraft observations and are capable of forecasting and extrapolating weather conditions between 30 to 60 minutes in the future. This case study has identified risks to aircraft in critical stages in flight associated with microbursts caused by convective activity.

It has shown that skepticism of lesser known weather phenomena caused complacency on the part of Federal Aviation Administration personnel as well as pilots and the meteorologists who supply the weather information prior to flight. This study has also identified other factors that led to the fatal result of Delta flight 191 at Dallas Fort Worth such as the late identification of contributing weather factors and the crew’s inability to make timely corrections due to a lack of information and training. Following Flight 191’s demise airports and FAA administrators implemented weather detection procedures and tools to identify and provide adequate notification to the aviation community but the need for training on interpreting these weather images and radar returns falls onto the shoulders of flight schools and airline administrators to ensure that all pilots have an awareness of these conditions and understand how to correct for them. Bibliography National Oceanic and Atmospheric Administration. Delta Flight 191 Incident at DFW Airport.

References

1. https://www.weather.gov/fwd/delta191 National Oceanic and Atmospheric Administration. What is a Microburst?
2. Retrieved from https://www.weather.gov/bmx/outreach_microbursts National Transportation Safety Board (15 August 1986).
3. Aircraft Accident Report. Retrieved from https://learn.liberty.edu/bbcswebdav/pid-26860875-dt-content-rid-322538952_1/courses/AVIA340_D01_201840/AVIA340_LUO_8WK_DEV_ImportedContent_20180907071446/AAR8605%20Delta%20191.pdf