Feature - Aircraft Icing for General Aviation...And Others

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by Paul A. Johnson, Civil Aviation Safety Inspector, Flight Crew Examinations, General Aviation, Civil Aviation, Transport Canada

Transport Canada wishes to maintain a high level of awareness within the civil aviation community on the hazards of flying with ice and snow adhering to the critical surfaces of an aircraft, and on flying into icing conditions. This article is primarily aimed at the general aviation pilot, but indeed applies to all pilots who fly in our tough climate, so please read on!

A very small amount of roughness, in thickness as low as 0.40 mm (1/64in.), caused by ice, snow or frost, disrupts the airflow over the lift and control surfaces of an aircraft. The consequence of this roughness is severe loss of lift, increased drag and impaired manoeuvrability; particularly during the take-off and initial climb phases of flight. Ice can also interfere with the movement of control surfaces or add significantly to aircraft weight, as well as block critical aircraft sensors. There is no such thing as an insignificant amount of ice.

Aircraft operating from smaller regional airports are generally de-iced by company personnel, or in some cases directly by the pilot of the aircraft, using a pressure sprayer containing an approved de-icing fluid. Aircraft must be de-iced shortly prior to takeoff. When operating under icing conditions from remote sites, aircraft operators are responsible for carrying the appropriate anti-icing and de-icing equipment on board the aircraft or storing the equipment at the airport. If conditions are too severe, pilots are prohibited from attempting a takeoff.

In all aviation operations, the pilot-in-command (PIC) has the ultimate responsibility to determine if the aircraft is in a condition for safe flight.

Ground de-icing and anti-icing procedures vary greatly depending primarily on aircraft type, type of contamination accumulation on the aircraft and freezing point depressant (FPD) or de-/anti-icing fluid type. Pilots should become familiar with applicable Canadian Aviation Regulations (CARs) and Standards, the procedures recommended by the aircraft manufacturer in the pilot operating handbook (POH), aircraft flight manual (AFM), maintenance manual and, where appropriate, the aircraft service manual. As well, they should comply with all company operations manual provisions.

Qualified fluids - A list of qualified de-icing and anti-icing fluids is included on the Transport Canada Web site in their Holdover Time (HOT) Guidelines. If reliable holdover times are to be achieved, only qualified fluids that are stored, dispensed and applied in accordance with the manufacturers' instructions are acceptable. The qualified fluids have undergone laboratory testing to quantify their protection and to confirm aerodynamic acceptability.

Manual methods - Reducing the amount of de-icing fluid used can have a positive impact on both the cost and the environment. Manual methods of snow removal should be used whenever possible, as long as safety is not compromised. There are a wide variety of devices available to assist in the removal of frozen contaminants from aircraft. Factors such as temperature, amount of contamination, wind conditions, and contaminant location must be taken into account when choosing the method.

Pilot removing frost manually on small aircraft
Pilot removing frost manually on small aircraft
Photo: http://www.cessna150-152.com/

Under extremely low temperatures, the use of glycol-based fluids is limited (refer to the fluid manufacturers' specifications for details). In these circumstances, manual methods may be the only option.

Note: Extreme care must be taken whenever manual methods are used, to protect the highly sensitive and often fragile sensors and navigation antennas. Also very vulnerable to damage are: pitot tubes, static ports, angle of attack sensors, and vortex generators. When sweeping or "pulling" contamination off an aircraft, care must be taken to use motions which pull contamination away from any openings, in order to avoid forcing the contamination into any openings on the wings or stabilizers.

Brooms - Probably the most commonly used and most readily available de-icing manual tool is the broom. Although a common household broom could be used, a larger, sturdier commercial variety is usually chosen. Care must be taken to ensure the bristles are sturdy enough to be effective, yet not so stiff as to do damage to the skin of the aircraft. The broom that is to be used to sweep snow from the aircraft should not be used to sweep floors, as this can introduce unwanted foreign contaminants and chemicals to the aircraft surfaces.

Brooms are very useful in cleaning windows and other sensitive areas (e.g. a radome) where the application of hot liquid is best avoided or prohibited.

Aircraft height requires that extra attention be paid to safety, especially when combined with the tendency to stretch the reach with a broom. If a ladder or other such device is used, personnel must be certain that it is well steadied. Slippery surfaces can make climbing somewhat dangerous.

Personnel have attempted to sweep snow from wing and tail surfaces while standing on these surfaces. This is an extremely unsafe practice with a very high risk of a slip and fall accident. As well, many surfaces are not stressed to support the weight of a person. The broom should be used in a pulling motion from leading edge to trailing edge.

Scrapers - The most common type of scraper used is the commercial variety used to remove accumulation from building roofs. Because the handles of this type of scraper will often make contact with the wing, care must be taken to protect the wing. This can be accomplished by covering the handle with a foam wrap. Normally best with wet heavy snow, the scraper should be used in a pulling motion from leading edge to trailing edge (i.e. lay the scraper high on the aircraft surface and pull towards you).

Also available commercially, and of similar benefit to the scraper, is the squeegee. Squeegees are generally available in a variety of sizes and have foam or a similarly soft material on one side and a rubber blade on the other side.

Ropes - Ropes are another method of removing contamination (usually light frost) from wings and horizontal tailplanes. The method requires two personnel and a seesaw motion back and forth across the surface to remove the contaminants. This method tends to polish thicker layers of frost, and under such conditions is not considered an acceptable method of preparing an aircraft for flight. This method would leave frost contamination on the critical surfaces prior to takeoff, which would not comply with CAR602.11 or CARs Standard622.11 [General Operating Flight Rules (GOFR)], and therefore, would not fulfill the "clean wing concept."

Portable forced air heaters - Heat from a portable forced air heater can effectively remove frost and ice from critical surfaces. These heaters are commonly found in remote and Northern Canadian locations, and are normally used to heat aircraft interiors and to pre-heat aircraft engines.

The operator directs the airflow from a flexible duct onto the contaminated surface and the combined effect of the heated air and low velocity airflow melts and evaporates contaminants.

This technique has the effect of briefly warming the wing surface and can cause snow or other contaminants to stick to the surface when precipitation is present. The operator must keep moving the duct to avoid overheating any spot, as these heaters generate enough heat to cause damage to de-ice boots and other equipment if directed at a single spot for too long. Any water tends to refreeze quickly, as no FPD fluids are used.

Hand sprayers - Extreme operational conditions often require specific solutions. Winter operations in the Canadian North pose their own problems due to the extremes in both weather and temperature. It has been noted that a number of air operators carry Type I fluids with them in the aircraft from station to station so that it is available. The containers in which the fluid is kept resemble the common garden insecticide sprayer. The fluid in this circumstance would appear to be kept at room temperature.

Small hand-sprayers can be used effectively
Small hand-sprayers can be used effectively
Photo: http://www.cessna150-152.com/

De-icing fluid is mixed with hot water to remove contamination from the aircraft. This is done from the top of the aircraft down and in a symmetrical fashion. Follow all guidance material listed in the flight manual for normal procedures. Don't forget the undercarriage and the assistance of other personnel.

CAUTION: Proper fluid coverage is absolutely essential for proper fluid performance. It is imperative that the personnel applying the fluid are properly trained and that a consistent fluid application technique is utilized.

Most aircraft ground-icing-related accidents have occurred when the aircraft was not de-iced prior to takeoff. The de-icing process is intended to restore the aircraft to a clean configuration so neither degradation of aerodynamic characteristics nor mechanical interference from contaminants will occur.

Takeoff after holdover times have been exceeded

In accordance with the operator's program, takeoff may occur after the holdover time has been exceeded only if a pre-take-off contamination inspection is conducted and it is determined that critical surfaces are not contaminated.

Subparagraph602.11(4)(a)(i) of the CARs states: "The aircraft has been inspected immediately prior to take-off to determine whether any frost, ice or snow is adhering to any of its critical surfaces."

Section6.3 of CARs Standard622.11 states, in part: "When holdover time tables are used as decision making criteria, take-off after holdover times have been exceeded can occur only if a pre-take-off contamination inspection is conducted, or the aircraft is de-iced/anti-iced again."

Transport Canada's interpretation of the phrase "inspected immediately prior to take-off," in the ground icing context, is that the inspection must be conducted within five minutes prior to beginning of the take-off roll.

This practice is not intended to be used continuously every five minutes, but as a one-time only condition after holdover times have been exceeded.

If, after conducting the contamination inspection, it is not possible to take off within five minutes, the aircraft must return for de-/anti-icing.

Failed fluid recognition

A fluid is considered failed when it is no longer able to absorb frozen precipitation. Under these circumstances, it must be assumed that the contamination is adhering to the critical surfaces.

Failed fluids can be difficult to recognize, in that a layer of clear ice may have formed under the fluid. This clear ice can usually only be detected by a tactile inspection. A failed fluid will usually lose all its glossiness and have a dulled crystalline appearance. While snow on a wing may be readily apparent, the clear ice that may have formed underneath is not. Snow that has accumulated on a wing on top of de-/anti-ice fluids means the fluid has failed and will not "blow off" on the take-off roll. Similarly, when used alone, TypeI fluid can refreeze in a matter of a few minutes after the holdover time has expired under certain precipitation conditions (especially freezing drizzle and freezing rain). The appearance is of a dulled rough coating of frost. Upon recognition of a failed fluid, the aircraft must return for further de-/anti-icing or the takeoff must be delayed until the weather improves and the contamination melts.

Action view from the cherry-picker's position
Action view from the cherry-picker's position

Here are some recommended media products available from Transport Canada:

  • Our video classics When in Doubt...Small and Large Aircraft, Aircraft Critical Surface Contamination Training (TP10643E) and When in Doubt...Ground Crew - Aircraft Critical Surface - Contamination Training (TP10647E) are available in either CD-ROM or VHS format.
  • The Icing - Awareness and Training CD-ROM (TP14189E). This recently-released CD-ROM newsletters articles, a PowerPoint presentation on winter flying, all of which speak to various aspects of runway conditions or aircraft performance during winter operations. In the video Plane Talk on Ice, a group of concerned professionals - airline pilots, light airplane pilots, helicopter pilots, flight attendants and ground crew - has gathered in a hangar to talk about ice contamination and ways of dealing with it. The group discusses such things as poor crew communication, stress, inadequate ground procedures, corporate pressure and the effects of contamination on aerodynamics. (Note that Plane Talk on Ice is also available individually as TP13637E in VHS format only).
  • Icing for General Aviation Pilots (TP14041E) and Tailplane Icing (TP13658E) were produced as a collaborative effort between the National Aeronautics and Space Administration (NASA) Glenn Research Center, the United States Federal Aviation Administration (FAA), and the Aircraft Owners and Pilot Association (AOPA) Air Safety Foundation. Both of these products were subsequently adapted in French by Transport Canada Civil Aviation. (To learn more about the Glenn Research Center's Icing Branch, visit http://icebox-esn.grc.nasa.gov/).

    • Icing for General Aviation Pilots (TP14041E) presents practical information to help pilots avoid and detect ice, minimize exposure, and safely exit icing conditions during each phase of flight. The effects of icing on aircraft performance and recovery procedures are also discussed. This video is available in CD-ROM, DVD or VHS format.
    • Tailplane Icing (TP13658E) provides information about ice-contaminated horizontal stabilizers and is intended for pilots who may encounter in-flight icing. The video presents a physical description of the tailplane icing problem, symptoms of ice contamination, and suggests recovery procedures. This video is available in either CD-ROM or VHS format.
  • Supercooled Large Droplets (SLD) Icing (TP 14342) is also a collaborative effort between NASA, the FAA, the Airline Pilot's Association (ALPA) and the National Center for Atmospheric Research (NCAR), with French language adaptation by Transport Canada. This video discusses the phenomenon of SLD icing for the professional pilot and other aviation professionals. Topics covered include how SLD icing conditions are different and exceed those required for aircraft certification; potential performance and handling hazards associated with SLD ice accretions; visual cues from the flight deck to aid early detection and escape; and finally where and how SLD form in the atmosphere to better anticipated this condition. This video is available in DVD format.
  • System Safety Winter Briefing Kit (TP14181). This collection of 14CD-ROMs contains various promotional products produced by System Safety headquarters and regional offices. This package was originally designed to provide the regional System Safety Specialists with a central bank of materials for the regional safety briefings. However, this collection could well serve industry in setting up their own safety briefings. This kit covers the following themes: 1.Runway surface and aircraft performance; 2.Icing awareness and training; 3.Meteorology and miscellaneous winter flying hazards; 4.Medical and human factors.

All of the products above can be purchased from the new Transport Canada Transact Web site at www.tc.gc.ca/transact, or by calling the Civil Aviation Communications Center at 1 800305-2059.

Here are additional icing references from the Transport Canada Web site:

Commercial and Business Aviation Advisory Circular (CBAAC) 0130R - Revised Airborne Icing Training Guidance Material http://www.tc.gc.ca/eng/civilaviation/standards/commerce-circulars-ac0130r-1762.htm.

CBAAC 0225R 'Ground icing operations update' and 'Holdover time guidelines'' http://www.tc.gc.ca/eng/civilaviation/standards/commerce-circulars-ac0225-1739.htm.

Finally, the 7thedition of the When in Doubt...Small and Large Aircraft Manual (TP10643E) dated December 2004 has been posted on the web at: http://www.tc.gc.ca/eng/civilaviation/publications/tp10643-menu-1118.htm.

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