In this context, you asked us to examine the trust-fund revenueforecasting process. To address your request, we examined (1) how trustfund revenues are forecast for the budget year; (2) the accuracy of past trust-fund revenue forecasts and the factors affecting forecast accuracy; (3) how different options for estimating appropriations from the trust fund might reduce the risk of overcommitting the trust fund; and (4) the extent to which trust-fund revenues might cover planned FAA expenditures in fiscal years 2012 through 2021.