A TIME-BASED APPROACH TO METERING ARRIVAL TRAFFIC TO PHILADELPHIA Todd Farley, John D. Foster, Ty Hoang, Katharine K. Lee Abstract Time-based metering via the Traffic Management Advisor (TMA) has significantly improved arrival operations at capacity-constrained airports in the western U.S. such as Dallas-Ft. Worth International Airport. Arrival flow management in the northeast corridor is in critical need of improvement to reduce the routine occurrence of airborne holding and in-trail spacing restrictions. However, the implementation and acceptance of time-based metering for a major airport in the tightly-constrained northeast corridor presents challenges beyond those encountered in other regions of the country. Research is underway at NASA Ames Research Center to identify these challenges, comprehend the underlying system dynamics, and develop requirements for a second-generation TMA system -- the Multi-Center Traffic Management Advisor -- intended to improve arrival operations at major airports in the northeast corridor. Philadelphia International Airport has been selected as the initial development and test site. Several research activities, including site visits and simulations, have identified four primary technical challenges of metering in this airspace: (1) an infrastructure that is inadequate for multi-facility coordination, (2) limited ability to absorb delay, (3) uncertain departure times of short-haul PHL arrivals, and (4) workload implications of converting from a miles-in-trail operation to a time-based metering operation. System requirements addressing these technical challenges are discussed.