NASA has developed the first simulator program for tail-plane (horizontal stabilizer) stall as the result of its research into icing and pilots have already used the program to train with the simulation to experience different stall characteristics induced by icing, whether wing stalls or tail-plane stalls.

More than 10 years ago, the National Aeronautics and Space Administration’s Lewis Research Center in Cleveland, OH conducted a four-year effort on the dangers of tail-plane icing. The Tail-plane Icing Program (TIP) yielded a wealth of data from which the space agency produced a 23-minute educational video that described the recovery procedure for tail-plane icing. The Tailplane Icing Program was only of one several research projects devoted to safe flight in icing conditions.

Also a decade ago, the University of Illinois at Urbana-Champaign’s (UIUC) Aircraft Icing Research Center undertook a Smart Icing Systems Project to identify and undertake the basic and applied research necessary to improve the safety of flight in atmospheric icing conditions.

The approach was to improve the ice tolerance of aircraft, high on the National Transportation Safety Board agenda. Indeed, the University of Illinois research went after just what NTSB wants – autonomous systems which will sense changes in aircraft performance and handling qualities and respond in a human centered fashion to enable the aircraft to maintain control and flight safety. The funding for this research was provided by the NASA Lewis Research Center.

Successful ice tolerant concepts were first applied to aircraft in the 1930’s with the installation of pneumatic boots on aircraft wings. Since that time, ice tolerant aircraft icing research has focused on sensing ice, improved ice removal methods, ice physics and other very specific research areas. Icing research has not focused on safety in terms of an overall systems view of the problem.

Particularly lacking is the application of flight mechanics, aircraft control and human factors to the icing safety problem. But recent advances in digital control, cockpit instrumentation and computer-based automation make it possible to develop new approaches to ice tolerant aircraft design and operation.

According to the university researchers, “the important effect of ice on an aircraft is its influence on the performance, stability and control of the aircraft system. Safety will be achieved in an ice tolerant aircraft if the pilot/aircraft system can continue to maintain the desired flight path, with an acceptable safety margin, regardless of atmospheric icing conditions. “

They said one scenario for a systems solution to ice tolerant aircraft safety is:

• Sense the presence of ice accretion through its effect on measured aircraft performance, stability and control. Sense ice accretion and ice protection system performance. Provide the appropriate information to the flight crew.

• Automatically activate and manage the ice protection systems, and provide the pilot with feedback on the system status and behavior of both the aircraft and the ice protection system.

• Modify the aircraft flight envelope by use of the flight control system to avoid conditions where flight could potentially be uncontrollable. Notify the flight crew of this action and its implications for the flight envelope.

• Adapt the aircraft control laws to maintain clean-aircraft-like flying qualities to enable the aircraft to be safely flown within the reduced flight envelope. Notify the flight crew of this action and maintain good pilot-automation coordination.

“The Smart Icing System Concept is principally a better way to manage the ice protection system and the operation of an aircraft in icing conditions where some degradation in performance and control can be anticipated. However, this safety system or concept is not intended to operate in a vacuum from other, well established icing safety procedures,” a Smart Icing System technical paper emphasized.

The safest way to operate when icing conditions exist is, of course, to avoid these conditions. Another well-developed safety strategy is ice protection. The ideal system would anti-ice the entire aircraft such that no ice would accrete anywhere on the airframe or propulsion system. This, of course, is not practical. However, many aircraft have excellent ice protection systems, IPS, which combine de-ice and anti-ice systems to provide overall aircraft protection.

A Smart Icing System would work in unison with the IPS to provide an additional level of safety beyond that provided by a simple IPS system alone.

The proposed new icing safety system would serve as an Ice Management System (IMS) that would protect an aircraft from the changes in performance, stability and control which, if left uncorrected, can lead to aircraft accidents, the university researchers reasoned.

Ratvasky told Aviation Today’s Daily Brief that he “continues to work, as an aspect of the TIP, the development of a means of detecting anomalies on aircraft before a loss-of-control event takes place. We are taking the knowledge gained on the TIP to develop a health monitoring system in which a pilot gets warnings that he is approaching a tail-plane stall condition.”

He said the research effort is being undertaken in collaboration with the University of Tennessee Space Institute. In year three of the research, they are still in “the breadboard stage” of work. The initial phase of research has another year to go; and, it is unclear how many research phases will be required. Funding and sponsorship issues remain, he adds.

Although unclear when such a system could be certified for aircraft, Ratvasky says it can be fielded. “This is not pie-in-the-sky. This is a legitimate approach to enhancing flight safety, as the UIUC’s preliminary research showed.”

This new system would evaluate actual icing conditions on an aircraft in real-time and update the onboard stall protection systems, if necessary, providing information to keep the aircraft in a safe flight envelope,” said Ratvasky.

Today’s Colgan-related News

Pilot of doomed flight described as 'by the book'