SAFETY OF FLIGHT

Icing accidents persist even for experienced IFR pilots

Accretion vulnerabilities pose dangers that require awareness both on ground and aloft.




General Electric Global Research Center is developing nanostructured surfaces which are superhydrophobic, with nanotextured surfaces to repel water and prevent or delay the formation of ice and reduce its adhesion.

The second method involves a Technology Service Corp (TSC) prototype dual-frequency airborne radar system to remotely sense the hazardous inflight icing conditions. This system will integrate a Ka-band radar into a commercial X-band weather radar. Pilots need an onboard means to observe, in a timely manner, whether conditions ahead of the aircraft represent an icing hazard, so that evasive action can be taken.

This requires the additional ability to remotely measure cloud region temperature to an accuracy sufficient to determine if the temperature is in the range of 0°C to –10°C, ie, is in the liquid water supercooled region.

Given their geometry, the system is more promising for cumuliform clouds than for stratiform clouds.

If successful, this program will be a practical solution to the challenge of inflight icing detection that can be employed on most aircraft using current weather radars, including helicopters and RPVs.

An alternative method proposes use of multispectral geostationary operational environmental satellites (GOES), which show great promise as icing diagnosis tools.

Several algorithms have been developed using combinations of visible and long and short-wavelength infrared channels to determine locations of supercooled liquid cloud tops.
For many pilots, the challenge of icing detection has another perspective—determining whether the vertical stabilizer and tailplane are contaminated as an aid in distinguishing a tailplane stall.

Innovative Dynamics Inc (IDI) has developed an icing onset sensor using a thin film capacitive-based sensor that monitors airfoil icing. The sensor identifies 2 levels of icing conditions—trace and ice. A "trace" light alerts the pilot when a trace of ice has formed on the airfoil. An "ice" light warns that ice formation has grown to a thickness that can be verified by the pilot.

New anti-icing designs focus on the opportunities afforded by nanotechnologies. Special nanocoatings on aircraft engine parts could repel water and possibly ice. If the need for expensive, energy-intensive systems to prevent icing could be eliminated, large efficiency gains could be realized.

US R&D organization Battelle mixes conductive carbon nanotubes (CNTs) into aircraft paint to produce a lightweight, low-power anti-icing coating that is easy to apply and repair. (See photo on p 2.)

EADS Innovation Works is investigating water-repellent coatings to prevent ice adhesion and accretion. However, its results bring into question the recent emphasis on super-water-repellent surface formulations for ice formation retardation and suggest that anti-icing design must optimize the competing influences of both wettability and roughness.

Systems currently used for deicing aircraft are either pneumatic (boots inflated by air but subject to damage and erosion) or electrothermal (using heated air, which is expensive in terms of energy required). Cox & Co claims its lightweight, low-power electromechanical expulsive deicing system (EMEDS) is the 1st new ice protection technology certified for flight into known icing conditions by FAA in over 40 years. (See illustration below.)

IDI, in collaboration with NASA Glenn Research Center and Lockheed Martin, has developed electroimpulsive deicing (EIDI) systems for use on aircraft. A version of the system is currently in use on the horizontal stabilizer of the Hawker Beechcraft Premier I. EIDI systems use electromagnetic coils underneath a rigid or semirigid icing-prone surface to produce an impulsive force sufficiently large to debond and expel the ice.

Regulatory enhancements

Electromechanical expulsion deicing systems use actuators—typically installed beneath the skin of the protected surface—which, when activated, induce a shock wave that dislodges the ice.

In Mar 2011, EASA published a proposal to update the certification specifications for large airplanes (CS-25) and turbine engines (CS-E) for flights in icing conditions. This is expected to go into force in 2Q­2012.

In Sep 2011, FAA issued a new rule to enhance aviation safety by requiring scheduled airlines to install ice detection equipment in their existing fleets or to update their flight manuals to make sure crews know when they should activate their ice protection systems.

The new rule targets scheduled airlines with aircraft weighing 60,000 lbs or less. Since studies show that smaller planes are more affected by undetected icing or late activation of the ice protection system, it may be worth examining whether this rule should be applied to aircraft operated under other rules as well.

Conclusion

Icing is a hazard that has threatened aviation since the earliest days. So much has been learned from the 1994 crash of a Simmons ATR72 at Roselawn IN and the 2009 crashes of a Colgan DHC8-Q400 at BUF (Buffalo NY) and an Air France A330 in the Atlantic Ocean. Emerging technology pro­mises improved detection capabilities, more tolerant airplane designs and greater ice protection.

Nonetheless, experience shows that atmospheric conditions bordering the icing certification envelope merit further investigation. Moreover, as we learned from the PC12/ 45 accident near Butte MN, pilot decisions may still foil the sound defenses technology provides. In the meantime, for definitive guidance, pilots must consult the flight manuals, operating manuals and maintenance manuals as appropriate.

The overarching strategy is to couple the clean-airplane concept with superior decisionmaking and alternative planning. Icing is a serious threat for which the most effective solutions remain to be discovered.

Don Van Dyke is an 18,000-hr TT pilot and instructor with extensive experience in charter, business and airline operations. A former IATA ops director, he has served on several ICAO expert panels and is a Fellow of the Royal Aeronautical Society.


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