The in-situ turbulence reporting system addresses the limitations of the subjective pilot reporting system in reporting turbulent conditions. It is true that many reports do not add value to turbulence forecasts simply because they: are formatted incorrectly, "fall on the floor" due to controller or Flight Service workload, are subjective and very aircraft dependent, take too long to enter the system, or simply because there are so few of them, and they rarely provide "null" reports. Turbulence is a very dynamic phenomenon and reporting requires a quick, automated, and comprehensive process in order for nowcasts and forecasts based on these reports to be of value to aviation.

Scientific analysis and simulation studies targeting these limitations began in 1991 at NCAR/RAP, leading to the development of aircraft models and an engineering definition of an aircraft's dynamic response to atmospheric turbulence. It became clear that a pure atmospheric measure of turbulence that eliminates the dynamic aircraft and pilot response was needed to improve nowcasts and forecasts of turbulent areas. Further, it was necessary to report a pure atmospheric measure so that this metric could be applied to other categories of aircraft, given the wide range of responses across the spectrum of aircraft types, weights, and speeds. Analyses were performed to derive an adequate turbulence metric, and the turbulence eddy dissipation rate was identified as such a metric. Vertical acceleration was used as the main sensing parameter because most aircraft have the sensing hardware and report this parameter to a data bus.

The in-situ turbulence algorithm that relates the eddy dissipation rate to aircraft vertical acceleration has been developed in RAP. Initial verification of the algorithm was performed on data from a set of severe turbulence encounters by commercial aircraft as well as data from two NCAR research aircraft. Another opportunity to evaluate the software occurred in 1994 in Hong Kong. Data were collected on-board Cathay Pacific Boeing 747-400s as they approached Kai Tak Airport.

In 1995, initial meetings with U.S. airlines were held to ascertain interest and determine a path to operations for this new capability. United Airlines agreed to provide in-kind support for installing and testing the algorithm and software on B-737s and B-757s. Early in 1997, a contract was signed with AlliedSignal Aerospace in Redmond, Washington, to install and ground test a unique software build for these two types of aircraft. Bench testing of an end-to-end sensing and reporting system was completed in August 1997. The first aircraft was uploaded with the modified Aircraft Condition Monitoring System software shortly thereafter.

As of the end of 1999, five airlines have agreed to participate in the in-situ turbulence reporting program. Aircraft types will include the B-737, B-757, B-767, B-747, and B-777, well over 1000 total aircraft.

Research Leads: Larry Cornman and Tenny Lindholm