Tail Plane Icing Program

Following the traumatic loss of TWA Flight 800 in 1996, then- President Clinton put together a commission on aviation safety, from which NASA in 1997 began an Aviation Safety Program to address very specific areas of flying in a bid to reduce the accident rate, even as air traffic was anticipated to grow at record rates. The emphasis on safety came at a time when a 4-year program led by NASA with the help of the FAA to understand the phenomenon known as ice – contaminated tail plane stall, or ICTS, was a year away from wrapping up. The successful Tail Plane Icing Program provided immediate bene­fits to the aviation community and today is considered by veteran NASA
researchers as one of the Agency’s most important icing-related projects ever conducted.[1238]

According to a 1997 fact sheet prepared by GRC, the ICTS phenom­enon is "characterized as a sudden, often uncontrollable aircraft nose down pitching moment, which occurs due to increased angle-of-attack of the horizontal tail plane resulting in tail plane stall. Typically, this phe­nomenon occurs when lowering the flaps during final approach while operating in or recently departing from icing conditions. Ice formation on the tail plane leading edge can reduce tail plane angle-of-attack range and cause flow separation resulting in a significant reduction or com­plete loss of aircraft pitch control.” At the time the program began there had been a series of commuter airline crashes in which icing was suspect or identified as a cause. And while there was a great deal of knowledge about the effects of icing on the primary wing of an aircraft and how to combat it or recover from it, there was little information about the effect of icing on the tail or how pilots could most effectively recover from a tail plane stall induced by icing. As the popularity of the smaller, regional commuter jets grew following airline deregulation in 1978, the incidents of tail plane icing began to grow at a relatively alarming rate. By 1991, when the FAA first had the notion of initiating a review of all aspects of tail plane icing, there had been 16 accidents involving turboprop-powered transport and commuter-class airplanes, resulting in 139 fatalities.[1239]

Following a review of all available data on tail plane icing and inci­dents of the tail stalling on turboprop-powered commuter airplanes as of 1991, the FAA requested assistance from NASA in managing a full – scale research program into the characteristics of ICTS. And so an initial 4-year program began to deal with the problem and propose solutions. More specifically the goals of the program were to collect detailed aero­dynamic data on how the tail of a plane contributed to the stability of an aircraft in flight, and then take the same measurements with the tail contaminated with varying severity of ice, and from that information develop methods for predicting the effects of tail plane icing and recov­ering from them. To accomplish this, a series of wind tunnel tests were performed with a tail section of a De Havilland of Canada DHC-6 Twin Otter aircraft (a design then widely used for regional transport), both in dry air conditions and with icing turned on in the tunnel. Flight tests of a full Twin Otter were made to complement the ground-based studies.[1240]

As is typical with many research programs, as new information comes in and questions get answered, the research results often gener­ate additional questions that demand even more study to find solutions. So following the initial tail plane icing research that concluded in 1997, a year later NASA’s Ohio-based Field Center initiated a second multi­phase program to continue the icing investigations. This time the work was assigned to Wichita State University in Kansas, which would coor­dinate its activities with support from the Bombardier/Learjet Company. The main goal was of the combined Government/industry/university effort was to expand on the original work with the Twin Otter by com­ing up with methods and criteria for testing multiple tail plane configu­rations in a wind tunnel, and then actually conduct the tests to generate a comprehensive database of tail plane aerodynamic performance with and without ice contamination for a range of tail plane/airfoil configu­rations. The resulting database would then be used to support develop­ment and verification of future icing analysis tools.[1241]

From this effort pilots were given new tools to recognize the onset of tail plane icing and recover from any disruptions to the aircraft’s
aerodynamics, including a full stall. As part of the education process, a Guest Pilot Workshop was held to give aviators firsthand experience with tail plane icing via an innovative "real world” simulation in which the pilots flew with a model of a typical ice buildup attached to the tail surface of a Twin Otter. The event provided a valuable exchange between real-world pilots and laboratory researchers, which in turn resulted in the collaboration on a 23-minute educational video on tail plane icing that is still used today.[1242]