High-Altitude ADS-B/GPS LPV Flight Tests on a NASA ER-2 Research Airplane

The research presented in this paper describes the conceptual design of a system architecture that integrates
Automatic Dependent Surveillance-Broadcast (ADS-B) and Global Positioning System (GPS) Localizer Performance
Vertical (LPV) guidance technology onto a unique high-altitude research airplane: a United States Air Force
(USAF) / Lockheed Martin (Bethesda, Maryland) Aeronautics U-2S airplane. The design features modern display
capabilities to provide air-to-air surveillance and precision navigation, to adhere to Federal Aviation Administration
(FAA) certification standards for operations in upper Class E airspace.

The National Aeronautics and Space Administration (NASA) variant of the U-2S, now called the Earth Resources
(ER-2) airplane, remains unrivaled in the art of sustained high-altitude flight for scientific expeditions. Capable of
routinely cruising above flight level (FL) 650 that had been considered, at inception, the domain of only the most elite
experimental research aircraft types. Nicknamed the Dragon Lady, this U-2S research testbed is still one of the most
advanced aircraft in the world. The exceptional military design of the vehicle, security guidelines, and the performance
envelope of the ER-2 posed unique challenges to the integration of modern civilian avionics.

ADS-B epitomizes the next generation of surveillance technology, incorporating both air and ground aspects. ADS-B provides air traffic control (ATC) with a more accurate picture of the three-dimensional positioning of aircraft in various phases of flight, including en route, terminal, approach, and ground operations. The airborne surveillance system broadcasts its identification, position, altitude, velocity, and other information.

GPS LPV represents a significant advancement in aviation technology, emphasizing the pivotal role that GPS and
Performance-Based Navigation concepts will play in the foreseeable future. This technology represents a shift from
sensor-based navigation to performance-based navigation, allowing for more flexible and efficient use of airspace.

This research described herein is structured as follows: Section II, “Systems Background,” provides a systems
background and description of an ADS-B and GPS LPV system equipped on the high-altitude ER-2 research airplane
to satisfy the FAA airworthiness requirements for high-altitude flight operations. Section III, “Flight Test System,”
describes the flight-test airplane systems. Section IV, “Analysis of GPS SBAS, Safety, and Ground Tests,” provides
an overview of the GPS Satellite-Based Augmentation System (SBAS) and an analysis of the GPS LPV metrics,
safety, and ground tests. Section V, “High-Altitude Flight Tests,” describes the high-altitude flight tests, including
3 flight-test results, analysis, human factors, and lessons learned. Section VI, the conclusion, draws insights from the
lessons learned, discusses the design challenges associated with ADS-B and GPS LPV, and showcases the paramount
significance of these pivotal technologies in aircraft surveillance and navigation.