Cumulative Noise Index
Massport reports total annual fleet noise at Logan Airport, defined in the Logan International Airport Noise Abatement Rules and Regulations by a metric referred to as the Cumulative Noise Index (CNI). The index is a single number representing the sum of the entire set of single-event noise levels experienced at the airport over a full year of operation, weighted similarly to DNL so that activity occurring at night is penalized by adding an extra 10 decibels to each event. This penalty is mathematically equivalent to multiplying the number of nighttime events by each aircraft by a factor of 10.
The Noise Rules define CNI in terms of Effective Perceived Noise Levels (abbreviated as EPNdB) and require that the index be computed for the fleet of commercial aircraft operating at Logan Airport throughout the year. In addition, in each Logan Environmental Data Report (EDR) and Environmental Status and Planning Report (ESPR) Massport reports partial CNI values of noise at Logan Airport, so that various subsets of the commercial aircraft activity can be examined independently to identify which segments of the fleet (cargo, night operations, passenger jets, etc.) are creating the most noise.
Partial CNI values are obtained by summing the noise energy from particular subsets of Logan Airport's total operations. They are useful for identifying the greatest contributors to overall noise. These results are presented in attached table. The higher the partial CNI, the greater the contribution to total noise.
Carriers have been in full compliance with Federal Aviation Regulation (FAR) Part 91 since the end of 1999, when they were required to convert all aircraft weighing more than 75,000 pounds to Stage 3 status; however there continues to be a phasing out of the Stage 2 aircraft weighing less than 75,000 pounds.