In-Flight Icing and How Airlines Are Coping

Abstract

The hazards posed by in-flight icing are an important issue in commercial aviation. Extensive research into methods for coping with in-flight icing has been continuing for many years. This paper addresses the issues pertaining to in-flight icing including causes, impact on commercial aviation, and initiatives undertaken to avoid in-flight icing mishaps today and in the future. INTRODUCTION During 20 minutes of cruise flying in icing conditions, the airplane's speed decreased from about 200 knots to 158 knots. Just three seconds after the captain uttered 'severe icing,' the airplane's stall protection system activated. The radar track of its flight showed the airplane falling with the dead weight of a brick at a rate of more than 22,000 feet per minute. The circumstances are similar to those of other events involving various airplane types in cruise, hold, climb or even descent7'(Dow, 2003, p.1). The crash of TranAsia Airways Flight GE791 is under investigation by the Aviation Safety Council (ASC) of Taiwan. Recently, the ASC issued a bulletin calling upon French manufacturer Avions de Transport Regional (ATR), and on regulatory authorities in Taiwan, France and Canada to emphasize training in crew awareness of icing conditions (Dow, 2003). The pilots commented they were in severe icing 73 seconds before the abrupt end of the cockpit voice recording. The progression from concern to genuine alarm is all too familiar. They might have recovered with a descent to warmer levels. Not to go for a rapid descent is to invite the classic stall, upset and spin. Once the airplane starts to auto-rotate into a spin, recovery under the disorienting conditions at night-as in this case-would have been difficult. If crews miss the insidious rearward motion of the elevator trim wheel (or indicator) as speed bleeds off and angle-of-attack increases to compensate for increased drag, maybe yet another warning system is in order (Dow, 2003). John Dow, a recently retired Federal Aviation Administration (FAA) expert on in-flight icing, said he could wallpaper a room with digital flight data recorder tracings of icing incidents and accidents that look like this crash, based on the details at this early stage in the postmortem-the steady erosion of speed, the increase in nose-up trim by the autopilot, perhaps the final addition of power, and the wrenching roll and departure from controlled flight (Dow, 2003). Dow has described the nature of icing as one where the insidious trap is set when stall speed increases from ice buildup on the wing, and then the trap is sprung on a surprised crew. With insufficient available thrust, the crew would be unable to accelerate while remaining in level flight and so would need to unload the airplane by applying nosedown elevator. This method of escape increases airspeed and reduces angle-of-attack away from the deadly stalling angle--where lateral control easily can be lost (Dow, 2003). Where to Expect Icing Winter weather patterns provide all the right ingredients to produce major problems with icing. Icing can occur in both stratiform and cumuliform clouds, but in winter, it's more likely to be encountered in solid overcast, stratiform clouds, spread over hundreds of miles. Cumuliform clouds, in contrast, can produce more intense icing, but the icing conditions are relatively isolated, especially in winter. Notably, cumuliform buildups, embedded in warm front stratus clouds, can cause serious icing (George, 2003). JAAER, Spring 2004 Page 33 1 Golding: In-Flight Icing and How Airlines Are Coping Published by ERAU Scholarly Commons, 2004