A decade after an ATR-72 flying in icing conditions crashed into an Illinois soybean field, killing all 68 persons aboard, airplanes continue to fly into freezing rain and freezing drizzle conditions they are not certificated to handle, and which cannot be accurately forecast, a double exposure to risk.

Yet much progress has been made since the Oct. 31, 1994, crash of the American Eagle aircraft at Roselawn, Ill., although turboprop aircraft and smaller jets of the corporate variety continue to crash in icing conditions.

The nature of the icing threat remains the same. The "flying ice-block" phenomenon can occur suddenly, catching unwary aircrews who continue on occasion to fly in known icing conditions on autopilot, which can mask the per-formance degradation from ice buildup. Improved protections against airframe icing remain un-requited on the National Transportation Safety Board's (NTSB) "Most Wanted" list of aviation safety improvements (see ASW, May 17, 2003).

The NTSB's investigation into the crash at Roselawn spawned a broad range of safety recommendations. Those recommendations revealed the range and scope of the general state of unpreparedness throughout the industry a decade ago.

The reader is invited to skim the tabulation, just to appreciate the range of deficiencies uncov-ered in the Roselawn accident post mortem, not to mention the appearance of bureaucratic "process" dominating operational "progress" in the years since the accident. The sharing of critical technical and trend data remains a problem, despite the universal nature of the icing threat, as evidenced by the current "unacceptable response" status of NTSB recommendation numbers A-96-62 and A-96-64. The need for improved information- sharing was raised in the NTSB's Oct. 26 hearing on the crash of American Airlines Flight 587, indicating that the problem extends beyond the smaller aircraft that spend more time in icing to the big jets that fly above icing but are vulnerable to other misfortunes.

Yet much has been accomplished in the decade since the Roselawn disaster. According to various sources:

• There is an increased awareness and knowledge of the icing hazard throughout the industry today.
• Some manufacturers have provided improved de-icing boot protection, some aircraft models have been outfitted with ice detectors, stickshaker thresholds have been reduced when aircraft are operating with their ice protection turned on, and warning lights on some aircraft warn if airspeed drops below the minimum specified for flight in icing protections.
• More information is generally available about operations in icing conditions. For example, the National Aeronautics and Space Administration (NASA) has produced a series of readily available training videos on icing.
• The Federal Aviation Administration (FAA) has appointed a national resource specialist (NRS) for icing. This individual serves as the single FAA point of focus for ongoing research activity and helps spread the knowledge gained to the operational community.

Some points of contention remain. For instance, NTSB officials have recommended that autopilots be turned off when flying in known icing conditions, on the grounds that the autopilot's functioning can lull the crew while ice accretes on the airplane and stall margins melt away. Some operators counter that turning off the autopilot increases pilot workload

There is a greater awareness today that all icing is not the same. Freezing rain and freezing drizzle can involve supercooled large droplets, or SLD. The prime document for certifying aircraft performance in icing conditions is known in the industry as Appendix C to the current Federal Aviation Regulations (FARs). Appendix C covers most types of icing conditions, but significantly not SLD.

John Dow, a former FAA official who participated in the Roselawn crash investigation, believes that pilots still need to be better trained to cope with in-flight icing:

"Current training for turboprop pilots in post stall recovery is to apply power and maintain pitch attitude at first sign of stall (stick shaker or stall warning). While current regulations allow for minimum altitude loss, in simulator sessions, any altitude loss is grounds to fail the session.

"However, the increased drag on an ice contaminated airplane and the reduced margin of excess thrust may not allow the airplane to accelerate to a lower angle of attack, particularly at higher altitudes. Upset - with protracted roll oscillations, marginal airplane control in unusual attitudes, usually in instrument meteorological conditions (IMC) - often results in uncontrolled flight into terrain.

"The solution for the vast majority of icing upset accidents and incidents is straightforward. Immediately upon stall warning, uncommanded movement of the ailerons, uncommanded roll, buffet, or other aerodynamic cues, promptly move the pitch control to nose down, level the wings while advancing RPM and torque, until reaching sufficient airspeed for the type and recovering. If unable to lower the nose, extend flaps from the cruise configuration, level the wings, and advance RPM and torque. With this return to basic recovery, hundreds of lives including the 68 at Roselawn could have been saved, even though Roselawn was not a wing stall but a hinge moment shift from the buildup of ice on the wing."

One source said only about 1 percent of the flights into icing conditions expose airplanes to SLD, "but that's where the accidents continue to happen." It is also the regime where it is difficult for pilots to tell that they're flying in SLD conditions. In this type of icing, the airborne droplets slap and stick on the airplane, and in areas where the buildup will not be shed by current ice protection systems. SLD excrescences can form a ridge behind the protected area covered by the de-icing boot, forming a ridge that can totally negate effective aileron control.

The NTSB's recommendation to expand the Appendix C certification envelope to include SLD is some eight years old.

The FAA has charged the Aviation Rulemaking Advisory Committee (ARAC) to propose rulemaking that would ensure safe operations in freezing drizzle and freezing rain aloft and near the ground, specifically addressing exposure to SLD.

An ARAC Ice Protection Working Group is working to define an SLD icing environment for certification purposes. This initiative likely will result in a separate appendix to the FARs, as Appendix C includes rotorcraft. A notice of proposed rulemaking (NPRM) is expected sometime in 2005. If and when the new SLD standard ultimately is adopted, the question of applicability arises. For example, can new aircraft designs be approved only to Appendix C, not the new standard, if ice detectors are installed? That's one option making the rounds.

Meanwhile, those drizzle drops larger than certification standards remain a killer threat. >> Dow, e-mail jdowsr@earthlink.net <<

Roselawn Remembered - A Mortal Stillness Broken by the Rustle of Blowing Pages

John Dow, an icing specialist with the FAA before his retirement, visited the Roselawn crash site on Nov. 2, 1994, two days after the crash. At the time he was part of the NTSB performance group for the on-site investigation. He revisited the site two days after the 10^th anniversary memorial service. He offered this vivid recollection of his first visit to ASW:

"As I struggled to make sense of the carnage and debris at the accident site, I came across a book next to the largest piece of wreckage, the tail. Its curled pages were blowing back and forth under the cool sunny skies. It was a Bible. The wind blew the pages between Job 32-37 back and forth, capturing my attention.

It was the only movement from the remains of 68 people, their luggage, and the airplane that carried them. Later that night at the hotel, I opened the Gideon Bible and read those chapters. They comprise Elihu's address about the catastrophes that befell Job and arguments about the continuing debate of right and wrong and the state of man and the authority of God. The passages talked of storms and ice and other calamity. It was one of the few places in the Bible where the word 'ice' appears. What an ancient and eloquent introduction to one of the most pivotal icing accidents in aviation."

Photos: Dow

The Flying Ice-Block Syndrome

The problem is exactly as it has always been

1. Medium turboprops normally operate at altitudes from 12,000 to 25,000 ft., putting them into heavy weather (and icing) en route.
2. Flight crews don't "see" it happening. Some turboprops feature high wings (because of the propellers), which means the critical upper surface is out of view. Icing can happen quickly, day or night. A clear (transparent) ice accretion can begin silently as soon as the airplane enters a region of icing.
3. Wing, fuselage and empennage induced drag and profile drag rise rapidly, speed drops off and stalling speed rises rapidly.
4. Asymmetry of spanwise lift (due do non-symmetrical left/right wing icing caused by port and starboard rotation direction of the props) can induce one wing to stall first at a quite higher speed than normal. Stall warning systems don't always operate reliably.
5. The aircraft auto-rotates into a spin. Any possible recovery is complicated by the dissymmetry of icing on the wings and horizontal stabilizer - and the fact that autopilot- run elevator trim is somewhere well aft of normal by the time the pilot wakes up and disconnects the autopilot. Center of gravity will also have moved some. The surprise factor is also conclusive. Many turboprop pilots will have carried out very limited single-engine spin recovery early in their training, and always from an intentionally entered slow speed induced auto-rotation (where the aircraft had to be held in the spin or it would recover itself).
6. It happens quickly. In the Dec. 21, 2002, icing-related crash of a Trans Asia ATR-72, a mere 73 seconds elapsed from the pilots' recognition of severe icing to the sudden stop of the cockpit voice recorder (see ASW, Feb. 3, 2003).

Compiled from multiple sources