Whether, for purposes of calculating additional rent owing from the Port Authority to the City, inclusion in the Port Authority’s gross income of passenger facility charges (PFC) collected pursuant to 49 USC § 40117 would violate the prohibition against impairment of the use of such revenues in 14 CFR 158.7 (a) is not an issue that the City seeks to arbitrate, and would not become an issue unless and until the Port Authority is required to expend such revenues or the interest earned thereon as additional rent. However, whether such revenues should be included in the definition of gross revenues used to calculate the amount of additional rent due the City from sources other than PFC revenues is clearly an accounting question within the ambit of the parties’ arbitration agreement, and, accordingly, the petition to stay arbitration was properly denied. Concur—Sullivan, J. P., Rosenberger, Rubin, Nardelli and Williams, JJ.