System Level Risk Analysis of New Merging and Spacing Protocols

Chauncey Starr Senior Fellow Roger Cooke and researcher Tina Singuran recently conducted a system-level risk assessment of new merging and spacing (M&S) protocols for the Aeronautics Systems Analysis Branch at NASA’s Langley Research Center. This assessment will help aviation researchers design safe, efficient plans to accommodate expanding system capacity in the civil aviation sector.

U.S. aviation system capacity is forecast to grow by 4.4 percent per year until 2020, according to the Federal Aviation Administration. Historically, growth in civil air traffic volume has been paired with a decrease in accident rate per flight. A major focus of NASA’s aeronautics research is the design of infrastructure and technology to accommodate this growth in volume while also reducing the accident rate per flight.

RFF Chauncy Starr Senior Senior FellowThe new M&S protocol being designed would merge arriving flights from different altitudes and directions during the en-route phase and deliver that arrival stream precisely to the runway threshold using optimized flight profiles within minimal speed changes.

While many studies have focused on the performance of the new concept, the evidence regarding its risk has been largely anecdotal. The main stumbling block has been the absence of a system-level model for risk. Such a model was recently developed under contract with the Dutch Ministry of Transport. This model predicts the accident probability per flight as a function of some 1,300 variables, and incorporates all relevant observational data.

After carefully analyzing the risk impacts of the M&S protocols, Cooke and Singuran were able to adapt this model to reflect changes induced by the new M&S concept. Relative to the current design and technologies, the protocols are predicted to achieve a 14.4 percent reduction in risk. This is the first time that a system-level risk model for civil aviation has been used to quantify the risk benefits of a new technology. As design horizons shorten and margins tighten, it is becomes increasingly advantageous to inject a quantitative risk perspective as early as possible in the design process.