Progress in development of an Airborne Turbulence Detection System

Aircraft encounters with turbulence are the leading cause of in-flight injuries and have occasionally resulted in passenger and crew fatalities. These encounters also have significant economic impact costing the airline industry at least $100 million per year. To alleviate this problem, the Turbulence Prediction and Warning Systems (TPAWS) element of NASA's Aviation Safety program has investigated technologies to detect and warn of hazardous in-flight turbulence. As a result, a radar-based airborne turbulence-detection system (ATDS) has been developed, flight tested, and commercially installed for in-service evaluation on a Delta Boeing 737. Research and revenue flights have generated and continue to provide invaluable data that show highly confident turbulence detection capability, which improves upon existing commercially available systems. The new ATDS utilizes algorithms and hazard metrics developed for use with existing airborne windshear radar, and are designed to warn of hazardous, convectively induced turbulence even in regions with weak radar reflectivity (i.e. 5-15 dBZ).

Aircraft flying through turbulence will respond depending upon the fluid scale of motion, aircraft type, altitude, air speed, and weight. Thus, different aircraft may respond dissimilarly to the same turbulence field. Therefore, efforts were focused to establish a relatively simple but robust aircraft turbulence hazard metric that performs over the aircraft's flight envelope. Significant progress was made early in the TPAWS project with the development of the aircraft turbulence hazard metric. This metric quantifies the impact of turbulence on the aircraft and its passengers.

NASA installed a candidate ATDS on its own experimental aircraft and flight tested the system on a total of fourteen flights, logging over 50 encounters with significant turbulence, i.e. moderate or greater. It was determined that the experimental radar-based ATDS, along with its aircraft turbulence hazard metric algorithm, detected and correctly predicted the level of turbulence impact to the aircraft in over 80% of the events. In many of these events, radar reflectivity levels associated with the “turbulence patches” had levels that provided no reflectivity target on the crew's cockpit display. Soon after the conclusion of NASA's flight test, Delta Airlines and Rockwell Collins, under the technical guidance of NASA, invested resources to install a similar system on a revenue generating aircraft. Currently, this aircraft is collecting data from turbulence encounters and results are showing a level of performance similar to that in the NASA flight tests.

As data continues to be collected on the Delta aircraft, NASA, FAA, and industry partners continue to monitor the performance and developmental progress of the new system. Since the new system may incorporate alerting functionality, requiring flight crews to take procedural action in the event of a potentially hazardous turbulence encounter, radar manufactures are expected to file for FAA certification. To support the FAA in this activity, NASA has simulated a turbulence environment encountered on a flight test in April 2002 using the Terminal Area Simulation System (TASS).

In this paper, we will summarize the development history of the improved ATDS, including the aircraft turbulence hazard metric development, flight testing, and TASS simulations of the turbulence environments.