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Aviation Weather and Positioning, Navigation, and Timing (PNT) Applications

An airplane taking off over a body of water with a pier.
Aircraft wake vortices generated by an arriving aircraft into San Francisco International Airport. (Source: U.S. DOT Volpe Center)

About Us

The U.S. DOT Volpe Center’s Aviation Weather and Positioning, Navigation, and Timing (PNT) Applications Division has two core portfolios:

  • Aviation Weather – focuses on conducting measurements and associated analyses of aircraft wake turbulence, runway visibility, and associated weather/atmospheric sensing
  • PNT Applications – supports research for our cross-modal partners initiatives in the area of positioning, navigation, and timing.

Aviation Weather

Our team of engineers assists FAA in safely mitigating the adverse impact of overly conservative aircraft wake turbulence separation, as well as assessing new aircraft entering the national airspace system (NAS). This is done through implementations of large-scale and multi-year measurement campaigns focused on wake behavior, meteorological conditions, and flight tracks.

We collect and analyze data to identify the risks and benefits of new or improved operational procedures from the wake separation minima perspective. Our data-driven analysis process results in aircraft spacing that contributes to airport efficiency, resilience of the operations, environmental benefits, and maintaining, or even improving, the current level of wake separation safety.

The U.S. DOT Volpe Center team has been continuously involved and contributed to the wake turbulence separation research, optimization, and refinements in the United States, and in some cases internationally, since 1971. Many of the current FAA and international wake separation standards and procedures are either influenced or derived from U.S. DOT Volpe Center-conducted analyses. As the NAS continues to evolve and include more non-traditional flying vehicles, the U.S. DOT Volpe Center team works to further the demonstration of the safe reduction of wake separation minimum.

PNT Applications

Our team supports legislative and departmental PNT initiatives including the assessment of different type of interference to Global Positioning System (GPS) and the investigation of complementary PNT Technologies to support critical infrastructure. We are responsible for GPS signal monitoring coordination, U.S. leadership in Global Navigation Satellite System services. In particular, we lead and support efforts to consolidate the U.S. prototype applications, Dual Frequency Multi-Constellation Services, and Advanced Receiver Autonomous Integrity Monitoring development.

Our team also assesses and evaluates PNT needs of advanced future transportation systems such as Highly Automated Systems with emphasis on operational safety. We design, model, and simulate static and dynamic scenarios and evaluate them through multi-sensor real world data collection campaigns. We develop and implement advanced data fusion and analysis techniques to synthesize PNT information from raw sensor data. The team uses this information in a statistical analysis framework to evaluate and enhance the safety of current and future transportation systems.

Further, we support testing, development, and certification of airport equipment, including lighting and visibility sensors and PNT systems. To support testing activities, we operate the nationally recognized Aviation Weather Research Facility (AWRF) located on Joint Base Cape Cod, Falmouth, MA. The AWRF is a 155-acre test range famous for its fog, gusty winds, and overall variable weather. Installed weather instrumentation includes sensors to measure visibility, present weather, temperature, relative humidity, pressure, and wind speed.

Our Capabilities

Environmental Analysis, Science, and Engineering

  • Conduct aircraft wake measurement and behavior analysis
  • Analyze natural hazards and extreme weather
  • Develop state-of-the-art meteorological and wake-sensing algorithms, processing, and analysis tool suites to support the development of new, efficient, and safe wake turbulence separation minima
  • Develop meteorological and in-situ remote sensing of airplane wake vortices at multiple airports for wake characterization in operational, real world conditions
  • Conduct meteorological analyses that support flight testing site selection and weather related flight rules
  • Provide weather sensor and system development support
  • Evaluate PNT sensor performance and conduct interference analysis through radio and optical propagation and attenuation modeling in various atmospheric and user environments
  • Conduct interference analysis assessment for systems operating in GPS-adjacent frequency bands
  • Assess the state of readiness of current and emerging PNT sensors for AV applications by defining Operational Design Domain (ODD)
  • Analyze performance and safety of PNT sensors and systems for AV applications
  • Assess the safety of PNT sensor suites for different ODDs by using optimal sensor fusion such as Extended Kalman Filter implementation
  • Conduct large scale tests of GNSS backup and complementary PNT technologies

Systems and Infrastructure Modernization and Optimization

  • Certify runway visual range sensors
  • Conduct advanced air traffic control procedure feasibility and benefit analysis
  • Evaluate PNT services
  • Develop PNT system requirements
  • Implement National Institute of Standards and Technology 8323 Cybersecurity Framework
  • Apply a wide range of data processing and statistical analysis techniques to develop and evaluate innovative enhancements to the national transportation system

Meet Our Team

View selected staff biographies

Stephen Mackey


Stephen Mackey

Steve Mackey is the U.S. DOT Volpe Center’s chief of Aviation Weather and PNT Applications. He leads a team of engineers supporting various government departments and agencies by helping them solve complex issues. The Aviation Weather and PNT Division team has expertise in conducting large-scale measurements and associated analyses, including aircraft wake turbulence, runway visibility, weather/atmospheric sensing. In addition, the Division is focused on GPS interference, complementary and automated PNT, and cybersecurity for PNT.

Since starting at the U.S. DOT Volpe Center in 2003, Steve has worked on various projects related to wake vortex analysis and optimal aircraft separation, flight technical error analysis, runway visual range characterization, evaluation of PNT technologies, and GPS interference. Mackey holds a BS in electrical engineering from the University of Massachusetts (Amherst, MA).

Andrew Hansen, PhD

Principal Technical Advisor for Aviation Modeling and System Design

Andrew Hansen

Andrew Hansen, PhD serves as part of our team of principal technical advisors who work across the U.S. DOT Volpe Center to identify emerging transportation technologies, conduct analyses and assessments on topics of national significance, and explore new opportunities in response to evolving national concerns.

Hansen serves as principal technical advisor for aviation modeling and system design. Read Andrew Hansen's full bio.


Frank Wang, PhD

Principal Technical Advisor for Wake Vortex

Frank Wang, PhD serves as part of our team of principal technical advisors who work across the U.S. DOT Volpe Center to identify emerging transportation technologies, conduct analyses and assessments on topics of national significance, and explore new opportunities in response to evolving national concerns.

Wang serves as principal technical advisor for wake vortex. Read Frank Wang's full bio.

Hadi Wassaf, PhD

General Engineer

Hadi Wassaf, PhD is an electrical engineer who leads the highly automated systems (HAS) and highly automated vehicles (HAV) sensing, modeling, data collection, and analysis portfolio for the division, with application to PNT and cybersecurity. His work directly supports the Office of the Assistant Secretary of Transportation for Research and Technology (OST-R) PNT directorate, Intelligent Transportation Systems Joint Program Office (ITS JPO), and the Highly Automated Systems Safety Center of Excellence (HASS COE). Wassaf has strong expertise and authored and co-authored multiple reports and papers in the areas of statistical signal processing and modeling for remote sensors, spectrum compatibility, radio frequency (RF) and optical signal propagation, Lidar algorithm implementation and modeling, Lidar pattern recognition and localization, acoustic beamforming and imaging, sensor fusion, and statistical analysis for safety assessment. He is an active member and liaison at Standard Developments Organization (SDO) committees. Wassaf holds a BS, MS, and PhD in Electrical Engineering from the University of Massachusetts (Lowell, MA).