The Preferential Runway Advisory System (PRAS) at Boston Logan International Airport was developed as a response to the pervasive issue of aviation noise that had long plagued communities surrounding the airport.

Aviation noise, while a technical issue in many respects, is fundamentally a quality-of-life concern for those living in the flight paths of major airports. As air traffic increased over the decades, the adverse effects of aircraft noise, such as sleep disturbances, health problems, and disruptions to daily life, became more pronounced. PRAS was introduced as a method to distribute noise impacts more equitably among surrounding neighborhoods.

However, it encountered significant limitations, particularly in light of the Federal Aviation Administration's (FAA) implementation of Performance-Based Navigation (PBN) and consolidated flight paths. The case of PRAS at Boston Logan illustrates the complexities and challenges that arise when trying to reconcile aviation efficiency with community well-being.

Origins

he origin of PRAS dates back to 1982, when Massport, the agency that manages Boston Logan Airport, sought to address the growing concern of aircraft noise by developing a system designed to distribute this noise more equitably. The goal was to prevent specific communities from bearing a disproportionate burden of the noise associated with takeoffs and landings. PRAS aimed to achieve this through two main components: setting runway use goals to manage the distribution of noise, and implementing a computer program that provided runway configuration recommendations to air traffic controllers. The system was enhanced in 1990 and adjusted several times in response to changing conditions and community feedback.

PRAS was based on the principle of using a variety of runway configurations, taking into account factors such as weather, wind direction, air traffic volume, and noise management goals. For example, in favorable weather conditions, air traffic controllers could choose runways that directed aircraft over less densely populated areas or over the water, thus minimizing noise exposure for residential areas. In essence, the system was intended to be a balance between operational efficiency and noise mitigation, considering the limitations imposed by safety and logistical constraints.

How PRAS Worked

The PRAS program operated through two key components:

1. Runway Use Goals: PRAS established a set of specific goals to achieve its noise distribution objectives. These goals outlined which runways should be used during different times and weather conditions to balance noise exposure across surrounding communities. By establishing preferred runway configurations, Massport aimed to reduce the frequency of overflights over any single neighborhood, ensuring that the burden of noise was shared among various areas.
2. Computer-Generated Recommendations: A computer program was used to provide real-time runway configuration recommendations to air traffic controllers. This program took into account factors such as weather conditions, air traffic volume, and PRAS's noise distribution goals. Based on these inputs, the system advised air traffic controllers on which runway configurations would be most appropriate to use in order to meet the established noise management targets.

Suspension and BLANS study

The situation at Boston Logan was further complicated by the suspension of the PRAS system in 2004, following an FAA radar system upgrade and the consolidation of the Boston Terminal Control Center at a new facility in Merrimack, New Hampshire.

Although PRAS had not fully achieved its intended noise abatement objectives, its suspension left a void in noise management strategies at the airport. During the Boston Logan Airport Noise Study (BLANS), which took place in phases from the early 2000s to 2016, efforts were made to evaluate and improve noise mitigation measures.

The BLANS process, which sought to develop an updated runway use program, encountered significant challenges in reconciling the diverse interests of stakeholders, such as airlines and air traffic control authorities. Operational tests of new runway use strategies were conducted between 2014 and 2016, but no consensus was reached, and the BLANS project ended without the adoption of a new comprehensive runway use program. This outcome underscored the difficulties in finding an approach that could effectively balance noise mitigation with the operational needs of Boston airport.

PBN and GPS flight paths

Despite its intentions, the PRAS system also faced significant challenges that limited its ability to effectively alleviate noise impacts. The fundamental issue was the inherent tension between the operational demands of an increasingly busy airport and the desire to equitably distribute noise exposure.

In practice, factors such as prevailing wind conditions, which dictate the direction for aircraft to take off and land, often limited the available choices for runway configurations. Air traffic management needs and safety considerations always took precedence over noise abatement goals, particularly during peak traffic hours. As a result, certain neighborhoods continued to experience concentrated noise impacts, leading to ongoing dissatisfaction among affected residents.

The issue became even more pronounced with the FAA's rollout of Performance-Based Navigation (PBN), a program designed to modernize air traffic control by using satellite-based navigation. PBN enables aircraft to follow more precise flight paths than traditional radar-based systems, allowing for more efficient routing and increased airspace capacity. While these changes benefited airlines, they also had the unintended consequence of consolidating flight paths over specific geographic areas. This consolidation meant that communities located under these new, narrower flight paths experienced a significant increase in aircraft noise, as a greater number of flights were concentrated into smaller corridors.

The introduction of PBN effectively diminished the noise-distribution benefits that PRAS was designed to achieve. Whereas PRAS attempted to spread noise over multiple areas by rotating runway configurations, PBN focused air traffic into defined paths, resulting in more concentrated and frequent noise exposure for certain neighborhoods. For residents living under these concentrated flight paths, the impact was substantial. The reduction in variability in flight paths meant that some communities experienced near-constant overflights, sometimes with aircraft passing overhead every few minutes. This consistency of noise exposure led to increased reports of sleep disturbances, stress, and other health issues associated with chronic noise exposure.

The consolidation of flight paths also posed challenges to the original goals of PRAS. The PRAS program was based on the assumption that it was possible to distribute noise equitably by varying runway usage. However, with PBN, the precision of aircraft navigation reduced the flexibility to make significant changes in flight patterns because any deviation from established paths could disrupt the tightly managed flow of air traffic.

Consequently, the runway rotation practices under PRAS became less effective in providing the intended relief, and some neighborhoods, particularly those situated directly under the newly established PBN flight paths, found themselves shouldering a disproportionate share of the noise burden.

Communities left in a void

The discontinuation of PRAS and the unresolved nature of noise management at Logan Airport left communities feeling that their concerns were not adequately addressed.

For neighborhoods that experienced frequent overflights, the lack of an effective noise mitigation program meant enduring the negative health and quality-of-life impacts associated with aviation noise.

Research has shown that chronic exposure to high levels of aircraft noise is linked to various adverse health outcomes, including cardiovascular disease, cognitive impairment in children, and increased stress levels. The inability of PRAS, and subsequent noise management efforts, to meaningfully reduce these impacts contributed to a sense of disenfranchisement among affected residents.

Moreover, the situation at Logan Airport reflects broader challenges faced by communities across the United States dealing with the implementation of PBN and the consolidation of flight paths. The shift towards air traffic management practices focusing on capacity has often come at the expense of local communities, who are subjected to increased noise levels without commensurate benefits. This trend has led to legal and political battles in cities such as Phoenix, Washington, D.C., and New York, where residents have pushed back against the FAA's changes to flight patterns.

The case of PRAS at Boston Logan highlights the need for more robust community engagement and consideration of environmental justice in aviation policy. While operational efficiency and safety are critical goals for the aviation industry, they should not come at the expense of the health and well-being of local populations.

Although PRAS is no longer in effect at Logan Airport, Massport continues to collect and report data related to the system's original goals. This ongoing reporting includes key statistics on runway usage patterns and noise relief efforts for communities near the airport.

Further reading and references

• "Boston Logan Airport Environmental Data Report 2022," Massport, May 2024.
• "Noise and Health Effects of Aircraft Noise," World Health Organization, 2018.
• "FAA's Implementation of Performance-Based Navigation," Congressional Research Service, 2020.