Wake turbulence from departing and landing aircraft pose a safety hazard, including aircraft operating on Closely Spaced Parallel Runways (CSPRs). Aircraft separation standards are imposed to mitigate this potential risk. The FAA and NASA are sponsoring a development program for establishing wind-dependent procedures for improved departure operations that safely reduce spacing restrictions to allow increased airport operating capacity. These procedures are referred to collectively as Wake Turbulence Mitigation for Departures (WTMD). An important component of WTMD is a Wind Forecast Algorithm (WFA) being developed by MIT Lincoln Laboratory which predicts when runway crosswinds will persistently remain favorable for WTMD procedures. For winds up to 300 m AGL (the nominal height at which aircraft departing from parallel runways diverge and alternate forms of separation standards are applied), the algorithm relies heavily on the NOAA/NCEP Rapid Update Cycle (RUC) Model forecasts at the 2 to 4 hour time horizon.

The performance suitability of RUC wind forecasts for this application is investigated. RUC crosswinds are compared with LIDAR measurement data collected at St. Louis Lambert International Airport (STL) in 2004 and 2006-2007. The results show that the RUC crosswinds generally correlate well with LIDAR measurements, with a mean difference of 0.4 m/s (s.d. 1.3-2.5 m/s) for both the RUC initialization data and the RUC forecast data. No significant degradation was observed at the longer 4-hour RUC forecast horizon, and the choice of RUC horizontal resolution from 40 to 13 km does not greatly affect the RUC crosswind estimation accuracy. On the other hand, the RUC crosswind accuracy decreases with height and frequent wind direction change. The primary reliability concern was found to occur during rapidly changing wind conditions associated with wind field discontinuities, such as during situations of convective outflow or synoptic scale frontal passages. Overall, our comparison of the RUC and LIDAR crosswinds at STL suggests that the RUC forecast can be a reliable source for obtaining crosswinds for the WFA. Future studies will include airports (e.g., San Francisco International Airport) whose local winds are more significantly affected by regional- or local-scale effects, such as thermally induced circulations (land-sea breezes, etc.) or topographical wind channeling.

This work was sponsored by the Federal Aviation Administration under Air Force Contract No. FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.