Aviation Weather Community | Engineering Dissertations

It is quite obvious that aviation plays a major role in today’s society. Aviation services have become vital to the nation’s economy, national security, and to the safety of life and property. In particular, aviation weather services prove useful because they are used to support our national defense and humanitarian missions, transportation of people and commerce, hurricane reconnaissance, and emergency medical helicopter missions. Basically every flight ranging from the newest student pilot to shuttle missions require some sort of weather-related screening for safety precautions before flight.

The aviation weather community is constantly improving data gathering and prediction products and services in order to reduce the rate of fatal aviation accidents. There are grand improvements on getting information to the user in a timely and mission tailored manner. Also of importance is improving provider and user training, and implementing sound weather decision making processes. According to a speech delivered by Samuel Williamson, Federal Coordinator for Meteorological Services and Supporting Research, “A new system designed to improve the flow of air traffic during severe weather helped reduce delays by seven percent last month” (Williamson, 2000).

Current technologies include: implementation of Flight Information Service (FIS) capabilities between the ground and cockpit; development and implementation of multifunctional color cockpit displays incorporating FIS products; expansion and institutionalization of the generation, dissemination, and use of automated pilot reports (PIREPs), including type of observation, to the full spectrum of the aviation community, including general aviation; improvement on weather forecasting services across all service areas; development and implementation of aviation weather-related training packages for Air Traffic Control service providers, pilots, and other users; improvement on aviation weather telecommunications capabilities for ground-to-ground dissemination of aviation weather products, including bulk weather data distribution; and finally improvement on objective standards for characterizing various weather phenomena for national and international use.

There are constantly major collaborative efforts in projects to update these technologies. Participating organizations include: The Federal Aviation Industry (FAA), The National Aeronautics and Space Administration (NASA), The National Oceanic and Atmospheric Administration (NOAA), United States Department Of Defense (DOD), and other industry, university, and association partners. The long a steady improvements in aviation safety experienced in the mid 80’s and early 90’s had plateaued out. Only through such collaborations are efficient and residual improvements possible.

This mesh of government and industry resulted in a four tiered planning process

Tier one began in late 1996, and is based around the sentiment that weather, in and of itself, does not cause accidents. It concentrated on creating better weather reporting and forecast to assist pilots, dispatchers, and controllers to make better and timelier weather decisions. Also included is to design and manufacture better aircraft. The result of that effort was the publication in 1997 of the National Aviation Weather Program Strategic Plan. Tier two was a matter of getting the details.

It concentrated on developing specific things that needed to be done in several areas and then to prioritize them according to their contribution either to safety or efficiency. The priority setting was very heavily weighted on the side of the air carrier operations. The result of tier two was the publication, in early 1999, of the National Aviation Weather Initiative. Tier three and four are proceeding concurrently and occupy the present moment. The focus of tier three is to identify who’s doing what, from the tier two activities, and then to find holes that need to be worked on.

Some of the projects require long-term infrastructure, development, and capital investment planning. Others are non-material solutions such as procedures or scientific research. Tier four consists of budgets and schedules. This includes actually securing the financial resources, allocating the personnel and fiscal resources, and establishing and track schedules.

In February 1997, the White House Commission on Aviation Safety and Security recommended a national goal for government and industry of reducing the rate of fatal aviation accidents by a factor of five per 100,000 flight hours, equivalent to an 80% reduction, within 10 years (OFCM, Ops. For Implementation pg.2-1). Safety research and technology improvements were recognized as essential elements in achieving this goal. Both the FAA and NASA adopted this proposal in their strategic plans.

The 1999 report by the Joint Action Group for Aviation Weather, National Aviation Weather Initiatives, included efforts underway in the aviation industry and programs with industry, academic, and governmental partners. Furthermore, it adopted the 80% reduction goal and suggested that a reduction in weather-related accidents, as shown by National Transportation Safety Board (NTSB) accident statistics, could be used as an overall measure of success for the current aviation weather initiatives.

In the proceedings of the aviation weather user forum in Bethesda, Maryland of 2000, four major objectives/goals were set for the Aviation Weather community: to highlight programs/processes which have been implemented recently, or are now ready for implementation, to identify ongoing programs which show promising results and must be supported with continuing resources to reach fruition, to illuminate gaps where no work in ongoing or planned, and to identify overlaps and assess them (OFCM, Ops. For Implementation pg.4-1).

In August 2003, the Office of the Federal Coordinator for Meteorology (OFCM) released the National Aviation Weather Program Mid-Course Assessment. The assessment adopted the 80% percent reduction in accidents as a benchmark for assessing progress and seeking areas where more effort, or a redirection of effort, may be worthwhile. It adopted the analytical approach of distributing the goal of an 80% reduction in fatal accidents across the three principal regulatory categories for aircraft and across categories for weather-related aviation hazards.

Flights of aircraft capable of carrying 10 or more passengers by a common carrier are regulated under Part 121 of the Federal Aviation Regulations. All noncommercial and nonmilitary aviation is covered under part 91. Revenue-generating flights not covered under part 121, including scheduled passenger service in aircraft with fewer than 10 seats and nonscheduled passenger and cargo service, are covered by part 135.

In 2002, there were no fatal weather-related accidents involving Part 121 aircraft. The rate per 100,000 departures for all weather-related accidents continued to decrease. Turbulence and convection hazards continued to dominate the weather hazards cited in Part 121 accidents. Of the nine weather-related accidents in 2002 involving Part 121 aircraft, seven involved turbulence and convection hazards. In the preliminary data for 2003, 11 of 12 weather-related accidents are in this category (OFCM, Programs/Projects 2004 pg.8).

The fatal accident rates for Part 91 accidents from all causes and for weather-related accidents increased in 2002 relative to 2001. However, the trend since 1997 for weather-related fatal accidents still achieves the goal of an 80% or higher reduction in accidents. The total weather-related accident rate also increased to the highest level (1.35 per 100,000 flight hours) since the 1998 rate of 1.43 per 100,000 flight hours. When the data are analyzed by weather hazard categories, the 2002 rates continued on a downward trend for precipitation (non-icing hazards). In the categories of restricted visibility, icing hazards, and en route and terminal winds, 2002 rates are higher than 2001, however a satisfactory downward trend is still in tact.

For turbulence and convection hazards, a small increase in fatal accidents leaves the trend on track to meet the 2006 goal. However, a larger relative increase for total accidents with turbulence or convection hazards cited as a factor has shifted that trend above its 2006 goal (0.29 versus 0.15 accidents per 100,000 flight hours). For temperature and lift, hazards, there were increases in 2002 much above the previous trend for both fatal and total weather-related accident rates. Neither trend would now meet an 80% reduction by 2006.

The increases in both total and fatal accidents were entirely due to high density altitude. The 2003 Nall report on accident trends and factors in the general aviation community, prepared and published by the AOPA Air Safety Foundation, found that visual flight rule (VFR) flight into instrument meteorological conditions (IMC) resulted in the greatest number of fatal weather accidents for the general aviation categories it covers. In the category of restricted visibility and ceiling hazards, of 67 total weather-related accidents, 50 involved fatalities, by far the highest percentage among the categories analyzed. These 50 fatalities represent 68% of the weather-related fatalities in all of Part 91. The hazard categories of precipitation, icing conditions, and temperature and lift hazards also had relatively high proportions of fatal accidents (OFCM, Programs/Projects 2004 pg.7).

The total weather-related accident rate for Part 135 aviation decreased in 2002, shifting the trend from an upward to a downward slope. The fatal accident rate and the trend were little changed from the previous year’s analysis in the Mid-Course Assessment. The hazard category trends observed continued with little change for the categories of restricted visibility and ceiling hazards, precipitation (non-icing) hazards, icing conditions, turbulence and convective hazards, and en route and terminal winds. For temperature and lift hazards, a second year in a row with no accidents has shifted the trend from and upward to a downward slope (OFCM, Programs/Projects 2004 pg.8).

National Aviation Weather Initiatives defined the eight service areas and 86 initiatives used in OFCM reports on Aviation Weather Programs and Projects. The initiatives are as follows: ceiling and visibility (14 initiatives), convective hazards (12 initiatives), en route winds and temperatures (7 initiatives), ground de-icing and anti-icing (6 initiatives), in-flight icing (15 initiatives), terminal winds and temperatures (11 initiatives), turbulence (12 initiatives), and volcanic ash and other airborne hazardous materials (9 initiatives) (JAG, Aviation Weather Initiatives. pg. 1-3).

In the case of ceiling and visibility, low reduced visibility is safety hazards for all types of aviation. The NASDAC study of NTSB statistics indicated that ceiling and visibility were cited as contributing factors in 24% of all general aviation accidents between 1989 and early 1997 (NTSB, Aviation Accident Database). They were also cited as contributing factors in 37% of commuter/air taxi accidents during the same period. Generally low ceiling and poor visibility accidents occur when pilots who are not properly rated or are flying aircraft not equipped with the necessary instrumentation encounter such conditions, resulting in loss of control or controlled flight into terrain. Ideally, aircraft should, with sufficient weather information and proper planning, be able to avoid conditions of low ceiling or poor visibility. In practice, this is not always possible.

However, a number of improvements should serve to make this service area more effective. Weather observation and reporting systems need to be expanded to provide better resolution for ceiling and visibility observations and forecasts. Capabilities for accurate measurement of runway visual range need to be extended to more airports and reporting systems developed to include this information in observation products. Capabilities for producing accurate localized forecasts of ceiling and visibility need to be refined for both civilian and military applications. Ceiling and visibility observations, analysis, and forecast products need to be provided to decision makers in clear and understandable formats, both textual and graphic.

Such products must be disseminated as rapidly as possibly to ATC providers and airline operations centers, especially during periods when conditions are changing rapidly. Pilot training must stress the need for constant awareness of current and expected ceiling and visibility conditions. Many accidents occur because pilots either underestimate the severity or conditions of fly into conditions they did not expect. Training for information providers should emphasize the dangers of rapidly changing ceiling and visibility conditions and help providers develop strategies for dealing with various scenarios that are likely to occur.

Convective hazards are associated with convective activity, such as thunderstorms and tropical cyclones, and also with clear air phenomena such as vertical currents caused by surface heating. These hazards include severe turbulence in and close to storms, intense up and downdrafts, lightning, hail, heavy precipitations, and tornadoes. Convective hazards pose a danger to both en route and terminal operations. According to the NASDAC analysis, between 1989 and early 1997 thunderstorms were listed as a contributing factor in 2-4% of weather related accidents. Precipitation was listed as a factor in 6% of commercial air carrier accidents, roughly 10% of general aviation accidents, and nearly 19% or commuter/air taxi accidents (NTSB, Aviation Accident Database).

Convective storms are a frequent occurrence throughout the U.S. at all times. Reducing the rate of accidents and delays relating to convective hazards requires ensuring that they are identified as quickly as possible and that sufficient information is disseminated to allow decision makers to plan avoidance strategies. Observations from a wide range of sensors need to be captured frequently and rapidly to identify convective storms as they develop. Once convective activity begins, data sampling rates need to be high enough to capture sudden storm intensification, tornadoes, hail production, and heavy precipitation development.

Algorithms to all more rapid assimilation of this information into models which produce accurate, timely, high-resolution forecasts need to be perfected. Users must have products that are accurate, reliable, and readily understood. Graphics and text-based products that are applicable to specific requirements can be invaluable to ATC service providers, aircraft operations managers, and aircrews for planning rapid responses to convective hazards. These products would be most valuable if they quickly portray the expected intensity, duration, and forecast path of convective activity, especially in the terminal area.

Winds and temperatures encountered en route play a role in determining the route an aircraft actually takes to reach its destination and how long it takes to get there. Pilots routinely take advantage of tail winds to increase over-the-ground speed while conserving fuel. On the other hand, head winds slow an aircraft’s progress and require increased fuel usage to maintain a planned schedule. Strong head winds can lead to delays, diversions, and, in some cases, accidents. Variations in temperature aloft cause changes in engine efficiency and flight characteristics in some aircraft, which in turn may require changes to the intended route of flight. The fundamental point is that pilots need to be continually aware of the changing nature of the atmosphere along their route in order to be able to react in a safe, efficient, and timely manner.

A number of improvements in this area are called for, primarily in the area of producing weather-related information. The primary issue is one of data density and accuracy. The only way to produce timely and accurate analysis and forecast products is to obtain as much accurate information as possible and assimilate it in a timely fashion. This is especially important over oceanic and remote regions where ground-based reports are sparse. More types and greater numbers of aircraft need to be equipped to send automated PIREPs to the National Weather Service and to the airline operations centers.

Aircraft-based reports of wind speeds, temperatures, humidity, and icing and turbulent conditions will prove to be a valuable adjunct to the existing network of observing stations. The observation network also needs to be expanded to include conditions at high levels and close to the ground. The comprehensive product suite developed for improved weather information needs to be delivered to users in formats that are both tailored to specific needs and readily understood without additional interpretation. Both graphical and textual products are needed as well as gridded products for computer flight planning systems. Communications systems need to be improved to deliver the products as rapidly as possible.

In the case of ground de-icing and anti-icing, aircraft on the ground during periods of freezing or frozen precipitation and other icing conditions are susceptible to the buildup of ice on control surfaces, instrument orifices, propellers, and engine inlets and interiors. Aircraft that are moving along taxiway and runway surfaces in slush or standing water at near-freezing conditions are also susceptible to surface contamination, even after the precipitation has stopped. Ice layers not removed from the wings and tail areas prior to takeoff can degrade lift and reduce the pilot’s ability to climb, even to the point of stalling the wing and causing an uncommanded descent, pitch, or roll.

Ice blockage or airspeed or altitude measurement instrumentation can cause loss of control or navigation errors. All airports should have adequate observations for the creation of products which provide a detailed local analysis of current icing conditions and pending changes. Data sampling rates should be increased during icing conditions in order to identify deteriorating conditions quickly. High resolution, small-scale forecasts are required to make ground icing information as accurate as possible.

All observation, analysis, and forecast products relating to ground icing need to be disseminated rapidly to a wide audience, and these products need to be tailored to the varying needs of recipients. These products also need to be distributed to airport managers, airline station managers coordinating flights, and ground de-icing crews in order for them to perform their tasks with maximum effectiveness.

In-flight icing is also very dangerous and has a major impact on the efficiency of flight operations. Similar to ground icing, rerouting and delays of commercial carriers to avoid icing conditions lead to late arrivals and the resulting ripple effect throughout the National Airspace System. Weather observation systems need to be expanded to provide higher spatial resolution for icing related variables, with particular emphasis on humidity and cloud data.

Observations, analyses, and forecasts of icing conditions need to meet specific standards of accuracy for geographical location and extent, as well as for duration and intensity. Improved precision will allow pilots and dispatchers to make avoidance planes with confidence. Icing observation, analysis, and forecast products should be in clear and understandable formats that can be transmitted to ATC and airlines operations center personnel as well as directly to pilots.

In general, pilots would benefit from improved understanding of icing conditions and the impact of ice accretion on airframe performance. Simulators capable of replication in-flight icing provide the best means of gaining this knowledge and experience under controlled situations. However, such simulators are not generally available for helicopters and small airplanes because of cost and large carriers do not currently simulate flight characteristics with ice accretions on airframe parts.

In the case of terminal wind and temperature hazards, weather hazards within the terminal area are dangerous because encountering them so near to the ground can require more altitude to recover than is available. The effects of these hazards on aircraft include unexpected motion in all directions, loss of aircraft control, and airspeed fluctuations that may induce aerodynamic stall. Variations in ambient temperatures in the terminal area can result in aborted takeoffs and inability to remain airborne once the aircraft is out of ground effect.

Weather observation networks within the terminal area must provide sufficient resolution in space and time to allow identification of rapidly moving gust fronts and severe turbulent cells that produce downbusts. Atmospheric conditions that determine the path of wake vortices, such as winds, temperatures, and stability, must be observed and measured. Current sensor and processor technologies under development offer the potential to provide significant amounts of low-level wind information. Commercially available, FAA certified wind shear sensors are slowly being installed in the commercial airliner fleet.

These devices will reduce wind shear-related accidents as more aircraft are equipped. Analysis and forecast products that decision makers rely on must provide information that can be rapidly understood. Graphics and text products can be of great use to aircraft operations and service providers for planning purposes and for alerting aircraft in the terminal area of hazardous conditions.

Non-convective turbulence is a major aviation hazard because all aircraft are vulnerable to turbulent motions. Non-convective turbulence can be present at any altitude and in a wide range of weather conditions, often occurring in relatively clear skies as clear-air turbulence. The effect of turbulence ranges from a jostling of the aircraft to sudden accelerations that can result in serious injury and temporary loss of aircraft control. Analyses and forecasts of regions of high turbulence can only meet specific standards for accuracy of geographic location and time duration if they are based on high-resolution observations.

Not only will possible satellite-based turbulence sensors and forward-looking sensors on aircraft themselves be invaluable to air crews, but, if they can be integrated into the normal data streams used for analyses and forecast models, they will greatly improve analysis and forecast accuracy. This level of accuracy will require observations that employ greatly expanded systems of fixed and mobile sensors that can provide data for finer-resolution forecast models.

Turbulence observation, analysis, and forecast products should be provided to decision makers in clear and understandable formats. Such products should relate turbulence location and intensity to geographical position, terrain features, and altitudes. The products must be easy to understand at a quick glance from the pilot, consistent in content across a range of providers, and available to the entire spectrum of decision makers.

Volcanic ash and other airborne hazardous material are not encountered as much as the areas, however, is it still largely a safety issue that is not overlooked. The combination of the pulverized rock and acidic gases found in volcanic ash can significantly affect the performance of jet engines at cruise altitudes. Ash clouds are often invisible, particularly at night. Some of the direct effects of ash include: fusing to compressor and turbine blades, leading to complete engine failure; abrading cockpit windows; abrading airframe and flight surfaces, thereby lessening aircraft performance; clogging the pitot-static system, producing inaccurate airspeed and altitude inputs to the navigation system; damaging the air conditioning and equipment cooling systems; and contaminating aircraft avionics and fuel.

A similar hazard to aviation can exist when accidental releases of radioactive materials or toxic chemicals into the atmosphere occur during and industrial or transport accident. Additionally, blowing dust and smoke from forest fires can cover large areas and pose a hazard for aircraft flying at low and mid-altitudes and taking off and landing at affected airports. Analysis and forecasts of volcanic ash trajectory and dispersion need to meet specific standards of accuracy for geographical location and extent, as well as for duration, especially at flight levels above 25,000 feet.

These forecasts need to include not only the projected trajectory of the ash cloud over space and time but also the flight levels that are affected. In addition, there is a need to understand the composition and density of the cloud. As forecast precision improves, pilots, dispatchers, and ATC providers can make avoidance plans with greater confidence. This improved precision will require resolution input data and finer-scale modeling tools.

Among the many programs being led by the FAA in the Department of Transportation, the Forecast Icing Potential (FIP) product became operational in March 2004. The FIP product is now available to the general aviation community, along with the Current Icing Potential (CIP) product, on the Aviating Digital Data Service website. FAA’s Graphical Turbulence Guidance product (GTG) product for flight level 200 and higher became operational in March 2003 for meteorologists and dispatchers. The Terminal Convective Weather Forecast (TCWF) product is an automated, one hour graphical forecast of convection intended for use by FAA traffic managers in terminal areas with high traffic density.

It has now been successfully tested at Dallas/Ft. Worth, Orlando, New York, and Memphis airports. In 2006, TCWF was installed at operational Integrated Terminal Weather sites. The Terminal Ceiling and Visibility (TCV) product, which provides automated forecasts for airports with chronic low ceiling and visibility risks, had its test bed trial in New York City airports in 2004. The Water Vapor Sensing System (WVSS) is a sensor system that automatically makes in situ water vapor observations from commercial aircraft on which it is installed and downlinks the data for use by weather forecasters. The WVSS became operational in May 2004.

During the first quarter of 2004, NASA’s Synthetic Vision System (SVS) has its initial flight evaluation for air transport. For this evaluation, SVS display concepts were integrated with concepts to prevent runway incursions. In 2005 the Terminal Prediction and Warning Systems (TPAWS) project had in-service evaluations of its Enhanced Turbulence Radar and the Turbulence AutoPIREPS System (TAPS). In NASA’s Weather Information Communications (WINCOMM) project, the next generation weather datalink technology had its initial lab evaluation during the forth quarter of 2004.

A flight evaluation of this datalink technology was performed in the third quarter of 2005. With a successful completion of ground and flight testing of a receiver and antenna in Johannesburg, South Africa, NASA has started to prepare for experiments using high-speed aircraft in areas of the world with limited access to timely weather data. NASA plans to provide a more advanced antenna design and consultation support. This successful test of real-time aviation-related weather data is a positive step toward solving communications-specific issues associated with the dissemination of weather data directly to the cockpit.

The Weather Research and Forecasting (WRF) mesoscale modeling activity is a consortium effort led by NOAA with support from other agencies and academia. WRF models continue to move into operational use in various applications, some of which have direct and significant impact on improving aviation forecasts. During 2004, a WRF version became operational at NOAA’s National Centers for Environmental Prediction and the Forecast Systems Laboratory. Implementation of a WRF model in the NCEP High Resolution Window began in October 2004. A WRF also model became operational at the Air Force Weather Agency in 2005.

Integrated Radar Data Services (IRaDS) began operations in August 2004. IRaDS is a collaborative effort to concentrate and transmit high-resolution weather radar data at cost for use by the private sector, government agencies, and researchers. Development of the Prototype Aviation Collaborative Effort (PACE) continued additional evaluations in the spring of 2005 for the Tactical Convective Hazard Product and Crosswind Tactical Decision Aid. The plan for this suite of products tailored for the needs of an air route traffic control center includes icing, turbulence, and ceiling and visibility products. NOAA is also collaborating with the aviation community on weather training for general aviation pilots.

The weather related accident data for general aviation underscore the importance of these efforts for reducing weather-related accidents. The Pilot Training Initiative (PTI), a collaboration with the Aircraft Owners and Pilots Association Air Safety Foundation and Meteorologix, provided live seminars nationwide in most U.S. in 2005. The PTI targets the general aviation community and Certified Flight Instructors. Another important part of the overall education and training for technology transfer, NOAA’s aviation operations course for National Weather Service aviation forecasters, became operational in Novembers 2004.

Through my research, I discovered that there were several themes which cross-cut all the presentations, discussions, and summaries on updating aviation weather technology. Products need to be requirements driven but resources are often the limiting factor to product development. As communication and display technology advance, graphical products are preferred over alpha-numeric. The time from development to operations needs to be minimized through rapid prototyping together with a process of pre-planned product development.

Training needs to be an integral part of product development and to increase the likelihood for success, the user need to be involved in the product development process. In the development process, there is a need for coordination, collaboration, cooperation and standardization among the agencies and universities to the maximum extent possible. Ensuring usability of products is important because they should be adaptable to varied users. A process of product validation should be established which ensures a quality product. As called for in the “National Aviation Weather Initiatives” document, there is a need to continue development of a capability, via applied research, to generate weather observations, warning, and forecasts with higher resolutions and accuracy.

This will require a concerted philosophy on the part of the aviation weather community toward the development and use of a wider array of sensors for mesoscale to microscale observations and products produced from fined scale models. The roles and responsibilities between the public and private sectors in product development, research and development should be reviewed. Finally, there is a need for consistency between products to facilitate meteorological discussion, determine impacts on operations, and facilitate the decision making process.

As far as perspectives for future steps, the groundwork has been done. The Strategic Plan provided the vision of a safer and more efficient National Airspace System and the National Aviation Weather Initiative have focused on specific areas where modest investments can reap significant benefits. It now falls to the agencies and the aviation industry to continue with the solution-based approach which will lead to continued support of existing programs and justification for new programs to satisfy the current initiatives.

Recommendations

• The need to develop a comprehensive National Aviation Weather Training

• The need for a comprehensive examination of the roles, missions, and functions between the private and public sectors in the provision of timely, accurate, relevant, mission tailored weather support to the full spectrum of aviation activities.

• The need for a review and improvement of the process for establishing, validating, and prioritizing requirements.

• The need to examine the coordination and collaboration process for research and development.

• The need to develop a coordinated process to assure that improvements in products, dissemination, and training satisfy requirements, are integrated and properly reflected in appropriate policy and procedures.

• The National Research Council should consider ways to review and report on progress by federal agencies on recommendations provided in the research council report, “Aviation Weather Services, A Call for Federal Leadership and Action”.

Bibliography

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Office of Federal Coordinator For Meteorological Services and Supporting Research. (July 2000). Proceedings of the Aviation Weather User Forum. Aviation Weather: Opportunities For Implementation. Held In Bethesda, Maryland On July 25-26 2000. Department of Commerce, Washington, DC.

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