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Near Repeat of Mirabel De-Icing Mishap

The following is a summary of an incident in the central de-icing facility (CDF) at the Macdonald Cartier International Airport (CYOW) in Ottawa, Ont., and was graciously provided by the CDF management team, which did its own investigation with hopes of preventing a reoccurrence. It brings back memories of the January 21, 1995, Mirabel, Que., tragedy, when a Boeing 747 departed the de-icing facility early and three de-icing operators in the cherry-pickers were killed when their baskets were tipped to the ground by the large aircraft. The Mirabel report can be found on the TSB Web site as file A95Q0015. -Ed.

On December 7, 2005, a Regional Jet CL600 was being de-iced in the CDF at CYOW, in preparation for a scheduled flight, with both engines operating. Two de-icing vehicles were in position at the tail of the aircraft, one on each side of the aircraft with booms raised and in the process of de-/anti-icing. The flight crew reported hearing that the flight was "clear." A request was made to ICEMAN (the CDF coordinator) for departure instructions. ICEMAN issued departure instructions to the flight crew. The aircraft exited the de-icing bay and proceeded on the west taxilane. The horizontal stabilizers of the aircraft narrowly missed contacting the de-icing vehicle booms. The de-icing vehicles and persons in the buckets of the booms did experience "jet blast." There were no injuries to the individuals in the buckets or damage to the de-icing vehicles.

Before departure, the flight crew was instructed to taxi to the CDF and contact ICEMAN on frequency 122.925. At 16:06 Eastern Daylight Time (EDT), the flight was positioned in a de-icing bay where two de-icing vehicles were waiting, and was instructed to contact SNOWMAN (the de-icing crew) on 131.075. Communications between the captain and SNOWMAN established that the aircraft was configured for de-icing operations. The operation was commenced, and the vehicle operators communicated with each other on 131.075.

At 16:21 EDT, the flight crew contacted ICEMAN to inform him that de-icing was complete, and to request departure instructions. After requesting, and receiving, verbal confirmation from the flight crew that all staff and equipment were away from the aircraft, ICEMAN gave departure instructions to the flight crew, to exit the CDF (via xyz route), and to contact ground control on 121.90. The aircraft proceeded as instructed. At that time, the de-icing vehicles were de-icing the horizontal stabilizers, positioned on either side of, and perpendicular to, the fuselage, and forward of the horizontal stabilizers. Immediately after this, ICEMAN was contacted by one of the de-icing vehicles, informing him that de-icing had not been completed and that both vehicles were de-icing the tail of the aircraft at the same time it had exited Bay 4.

The flight crew reported that SNOWMAN communicated to them: "Your holdover times started 30 seconds ago. You are clear." After receiving a confirmation of de-icing fluid mixtures from SNOWMAN, the flight crew also reported hearing SNOWMAN reaffirm: "You are clear, contact ICEMAN on 122.92 for taxi." In addition, the flight crew reported seeing SNOWMAN give a wave with his left hand, followed by a departure of the de-icing vehicle from the area. The flight crew reported looking left and right to confirm the area around the aircraft was clear. Subsequently, the flight crew requested, and received, departure instructions from ICEMAN. At the time of these transmissions, the elapsed time since the beginning of the operation matched the time usually required for this kind of de-icing operation.

Above anything else, de-icing operations require clear and precise communications between all involved
Above anything else, de-icing operations require clear and precise communications between all involved

The de-icing staff reported that they received a request from the flight crew regarding fluid mixtures, and reported also that the phrase "you are clear" was used during the de-icing operation. While the phrase "you are clear" is part of the communication standard operating procedures (SOP) for de-icing operations, it could not be determined at what time during the de-icing operation this had occurred. Other than the factual history details, the de-icing staff said this was the only reported communications between them and the flight crew.

Immediately after this, the aircraft engines were heard to increase thrust and the aircraft began to move forward, exiting Bay 4.


The VHF radios in the aircraft and de-icing vehicles functioned normally; however, there was confusion in communications between the flight crew and SNOWMAN that resulted in the captain believing that the de-icing was completed.

Decision to taxi

According to the International Civil Aviation Organization (ICAO), the following information must be given to the flight crew on completion of de-icing: the type of fluid used, the time of the last application, and confirmation that the aircraft complies with the clean aircraft concept. The flight crew released the brakes under the assumption that this information had been received. The flight crew reported hearing the words "you are clear" (de-icing completed). Although this message was not preceded by the flight call-sign or the de-icing crew call-sign, the flight crew reported hearing "you are clear" twice. The duration of the operation up to that point matched the time usually required for this type of de-icing. In addition, the flight crew reported seeing a wave of a hand from SNOWMAN and subsequently, the vehicle departing the vicinity of the aircraft. The flight crew assumed the de-icing crew had left the frequency and departed the area. The flight crew then advised the ICEMAN that the aircraft was ready to taxi, and, in doing so, conveyed to the ICEMAN that de-icing was completed and the aircraft was free of obstruction. Relying on that information, ICEMAN indicated to the flight crew their assigned route for taxiing. The flight crew further interpreted the issuance of taxi instructions as confirmation that the aircraft was free of obstructions.

Standard phraseology

According to the rules of standard phraseology, to avoid confusion, radio messages must be preceded by the receiving station call-sign, followed by the sending station call-sign. While these rules may not apply to interphone communications, the "open" nature of VHF radio communications requires that the international rules of radio procedure be followed. In this case, the flight crew reported hearing the words "you are clear" and made a number of erroneous assumptions: that the radio transmission was directed at them; that the de-icing operation was completed; and that all equipment and personnel were away from the aircraft's taxi path.

Coordination of communications

During de-icing operations, the operators of both de-icing vehicles communicated with each other on 131.075, and also with the flight crew on that same frequency; this allowed the flight crew and the de-icing staff to become confused during conversations.

Control of de-icing area

The CDF coordinator (ICEMAN) performed his tasks in accordance with established procedures and his assigned responsibilities. He guided the aircraft until it was stopped at its de-icing position. The aircraft came fully under the responsibility of the captain after it was stopped for de-icing. Before issuing taxi instructions to the aircraft, ICEMAN verified that the taxiway was clear. It was not his responsibility to consult the flight crew and de-icing personnel to determine whether de-icing of the aircraft was complete and the aircraft was ready to taxi. That responsibility was assumed by the flight crew when they declared the aircraft ready to taxi.

The fact that ICEMAN issued taxi instructions when de-icing was not completed indicates that he was not aware that de-icing was in progress. Although he fully discharged his responsibilities, ICEMAN probably did not have enough information or sufficient tools to accurately assess the situation in the CDF.


SNOWMAN performed the duties of marshaller and truck driver. He was not in a position to prevent the aircraft from advancing, given that he was behind the aircraft. In addition, SNOWMAN was not monitoring the ICEMAN VHF frequency of 122.925.

Several air carriers prefer to place a marshaller in front of the aircraft to minimize the possibility of the aircraft moving until the de-icing procedure is complete and all personnel and equipment are safely out of the way. Some carriers utilize an interphone cord plugged into the aircraft to maintain constant communication between the ground crew and the flight deck. This procedure eliminates the risk of confusion between flight crew/marshaller communications and other VHF communications. The de-icing contractor had not chosen the direct interphone cord method of communication because it was felt that the area around the aircraft was too dangerous an environment in light of the slippery footing conditions due to the glycol, particularly with the engines running.

Coordination between flight crew and flight attendants

The pilots did not report consulting with the cabin crew before releasing the brakes. Given that the pilots could not see the aft section of the aircraft from the flight deck, and they did not see if the de-icing vehicles had in fact departed the area, consulting the flight attendants was a conceivable and reasonable option in this particular situation.

In summary, it was determined that the flight crew started to taxi the aircraft before its perimeter was free of obstruction, following confusion in the radio communications.


  • The flight crew and de-icing staff did not use standard aeronautical terminology and phraseology on some occasions.
  • The flight crew assumed that the reported message SNOWMAN "you are clear" meant that the de-icing was completed.
  • The line of sight from the flight deck of the tail section did not allow the flight crew to be certain if the de-icing vehicles were away from the aircraft in the vehicle safety zones.
  • ICEMAN does not have a line of sight of the entire CDF at all times.
  • Following confusion in the radio communications, the flight crew started to taxi the aircraft before its perimeter was free of obstructions.
  • SNOWMAN was not in a position to prevent the aircraft from advancing, given that he was behind the aircraft where he could not be seen by the flight crew.
  • Several air carriers favour having a marshaller in front of the aircraft and using the interphone for ground communications during de-icing. This de-icing operator uses the VHF radio to communicate with the flight crew during de-icing operations.

Safety action taken

Clear communications between flight crews and de-icing staff was the key recommendation. All de-icing providers and all aircraft operators must review procedures with a focus on communication: protocols, practices and phraseology to be used. In particular, there should be an exclusion of the word "clear." Furthermore, the investigation recommended that radio communications between staff of de-icing operators be conducted on a separate, discrete frequency from the frequency used to communicate with the flight crew.

The CDF management team reviewed and made changes to the CDF SOPs. The procedures indicate that both visual and verbal communication must be received and acknowledged by aircraft flight crew prior to exiting CDF. These revised CDF procedures have been provided to all contract carriers, both at the local base and head office levels.

Cold Weather Altimeter Error-Getting Cold Feet?
by John Tomkinson

As happens every year at this time, everyone should be doing a review of their winter operational procedures, and dusting off the cobwebs from a summer of flying in a temperate climate.

Having discussed the coming winter with many fellow pilots and controllers over the past few weeks, I've found a recurring general theme. Nearly everyone can list hazards of icing, winter weather, slippery runways, and additional human factors, but whenever the topic of cold weather altimeter error comes up, I see more long faces than I should. Discussions in online forums show that most individuals have an idea of the implications that cold weather has on altimeter readings, but most can't get all the details correct, so here is our brush-up situation.

Cold weather altimeter error is operationally similar to flying from an area of high pressure to low pressure; the altimeter reads higher than it really is. The degree to which the altimeter misreads must be corrected by the use of charts available in the Transport Canada Aeronautical Information Manual (TC AIM) RAC Figure 9.1. Simple really, but there are common misconceptions about this procedure.

Firstly, this and other altimeter corrections are not done by ATC, but are the pilot's responsibility. Radar vectoring altitudes assigned by ATC are, however, already corrected for cold temperatures. This correction is done by airspace planners while establishing all minimum safe altitudes for use by ATC.

Secondly, any correction applied to a published altitude should be relayed to ATC. There is no minimum altitude correction that can be brushed under the carpet. Even the smallest corrections can make a big difference.

Corrections calculated by pilots are to be used to ensure obstacle clearance during final approach fix crossings, procedure turns, or missed approaches.

For those who have never used an altitude correction chart, here is an example of how the Canadian chart works. The minimum safe altitude for our example aerodrome with weather reporting is 3 000 ft, and the field elevation is 1 000 ft; therefore, the height above elevation of altimeter setting is 2 000 ft. The current aerodrome temperature is -30°C. Looking at the Altitude Correction Chart below, find the column representing 2 000 ft above the aerodrome with the row corresponding to -30°C for temperature, and the value required to be added to your altitude is 380 ft. To ensure that a published altitude of 3 000 ft will truly provide obstacle clearance, the altimeter must then be reading 3 380 ft. Additionally, in examples shown in the current TC AIM, the corrected indicated altitude is rounded to the next higher 100-ft increment, so our example would become 3 400 ft.

Sound like a small correction? Is it worth pulling out charts to cross reference while briefing the approach? In an accident report published by the Canadian Aviation Safety Board [now the Transportation Safety Board of Canada (TSB)], the hazards of failing to correct for even the smallest temperature error are clear. Fortunately, there were no fatalities in this incident:

"The helicopter was dispatched at night, in IFR conditions...The crew descended on the inbound leg to 150 ft, with reference to the pilot's altimeter. The helicopter struck the sea ice and was destroyed by post-impact fire. The crew had not applied a temperature correction to the minimum descent altitude [approximately 40 ft to as much as 100 ft. -Ed.], and this omission-combined with the known 50-ft error in the pilot's altimeter-accounted for the mistaken belief the helicopter was higher." (A81W0134)

A combination of high terrain or obstacles and low aerodrome temperature can easily wear down safety margins on your approach. Our above example has an error of 400 ft, meaning we would have no terrain clearance if we flew the published altitudes uncorrected.

So how can you know if your feet are cold? The following are the guidelines in the TC AIM.

According to TC AIM RAC Figure 9.1-Altitude Correction Chart:

With respect to altitude corrections, the following procedures apply:

  1. IFR assigned altitudes may be either accepted or refused. Refusal in this case is based upon the pilot's assessment of temperature effect on obstruction clearance.
  2. IFR assigned altitudes accepted by a pilot shall not be adjusted to compensate for cold temperatures, i.e. if a pilot accepts "maintain 3 000," an altitude correction shall not be applied to 3 000 ft.
  3. Radar vectoring altitudes assigned by ATC are temperature compensated and require no corrective action by pilots.
  4. When altitude corrections are applied to a published final approach fix crossing altitude, procedure turn or missed approach altitude, pilots should advise ATC how much of a correction is to be applied.

Altitude Correction Chart


  1. The corrections have been rounded up to the next 10-ft increment.
  2. Values should be added to published minimum IFR altitudes.
  3. Temperature values from the reporting station nearest to the position of the aircraft should be used. This is normally the aerodrome.

Everyone knows the old saying "high to low, look out below." As we enter another winter flying season, let's add another reminder phrase to our repertoire, "hot to cold, don't be so bold." Don't get cold feet in your altimeter this year!

John Tomkinson is an active air traffic controller in Toronto Center and a private pilot. He is also an aviation staff writer for

Storage, Labelling, Handling and Application of De-/Anti-Icing Fluids in Canada
by Paul A. Johnson, Civil Aviation Safety Inspector, General Aviation, Civil Aviation, Transport Canada

This is a follow-up article to Paul Johnson's "Aircraft Icing for General Aviation...And Others," which was published in the Aviation Safety Letter (ASL) 3/2005. Some readers asked us to clarify storage, labelling, handling and application of de-icing and anti-icing fluids.

The Canada Labour Code (CLC), Part II, is the legislation that ensures that the health and safety of all employees who are under federal jurisdiction while at work are protected. The Aviation Occupational Safety and Health Regulations (AOSHR), Part V, identifies the prescribed standards that must be adhered to with respect to hazardous substances, which include the de-/anti-icing fluids used in conjunction with ground icing operations.

At airports where de-/anti-icing is not available from a service provider, the de-/anti-icing may have to be completed by the pilot. Under these circumstances, pilots either have to carry the required de-/anti-icing fluid on board their aircraft, or purchase it on-site, so they can apply it to the aircraft themselves before takeoff. When the above situation occurs, it is both the operator's and pilot's responsibility to make sure the de-/anti-icing fluid is properly and safely stored, labelled, handled and applied.

Operators and pilots involved in de-/anti-icing operations are to familiarize themselves with the CLC Part II and AOSHR references, with particular emphasis placed on those sections dealing specifically with hazardous substances. In addition, Transport Canada's TP 14052E, Guidelines for Aircraft Ground Icing Operations, should be reviewed for recent developments and issues pertaining to aircraft ground icing operations.

The prescribed standards cover everything from the labelling of hazardous substance storage containers (section 5.28), to the requirement that operators must have material safety data sheets (MSDS) on board their aircraft for all hazardous substances an employee may handle or be exposed to, which include de-/anti-icing fluids.

For additional information visit:

Use only qualified fluids. These are the only fluids that holdover tables relate to. Use of an unqualified fluid risks fire hazards and unknown de-ice/holdover characteristics. For example, Isopropyl alcohol continues to be used as an aircraft de-icing fluid, especially in remote areas; however, it is classified as a flammable dangerous good. Only certain limited quantities may be carried on board an aircraft, and they must be labelled correctly and carried in approved containers. Training must be conducted in accordance with an approved training program and most importantly, no holdover time (HOT) exists. For more info, access:

Transportation of Dangerous Goods (TDG) Information:

The International Air Transport Association (IATA) Dangerous Goods Regulations Manual can be purchased at:

The International Civil Aviation Organization (ICAO) Technical Instructions for the Safe Transport of Dangerous Goods by Air can be purchased at:

The use of windshield washer fluid, aviation fuel or any other type of non-approved fluid is not recommended. These products have not been tested by any manufacturer and will not guarantee any degree of protection from snow or ice accumulation. Aviation fuel has been known to damage windshields, causing them to turn "milky," not to mention the increased fire risk. An engine stack fire during a cold start could ignite these fuel vapours quickly. Other non-approved fluids can cause damage to rubber seals and paintwork, necessitating expensive repairs.

Recommended de-/anti-icing practices for small aircraft operators

The key for smaller owners/operators regarding de-/anti-icing is prevention. Having a suitable hangar, or wing covers and tail covers, can save time and money when it comes to de-/anti-icing your aircraft. Many owners/operators do not have hangar space, but utilize wing and tail covers in winter to reduce their de-/antiicing times and expenses. They are great for frost, ice and snow coverage, but can "sweat" under certain atmospheric circumstances, and cause the covers to freeze to the surfaces they are protecting when the temperature drops again. These conditions are rare, and generally the covers are convenient for most small aircraft owners/operators. Installation usually requires two people, but can be done alone with a bit of practice. The covers should come off at approximately the same time. Removing one side and then the other to save time may lead to an accumulation of frozen contaminants on the side that was exposed to the elements first, and the pilot may not notice, or may fail to recheck for, these contaminants.

In some instances, small aircraft operators carry de-icing fluid on board their aircraft while traveling to remote locations where no de-/anti-icing facilities are available. The fluids carried must be tied down in a suitable location and labelled correctly in a secured container. Most garden-type sprayers are not suitable as a storage container, as they tend to leak from the pressure changes of a flight evolution. This would create a hazardous situation in the aircraft, a slipping risk for the crew, and a potential environmental accident. A recommended practice would be to carry the fluid in an appropriately-secured, labelled container on board the aircraft with an empty garden type sprayer on board as well (or located at the remote destination), and mix the appropriate concentration at the destination, using hot water. If possible, look for a sprayer with an immersible heater that can heat the de-icing fluid to the recommended temperature for application. Remember, it is the heat and spray force that melts the ice. Heated sprayers are available from aircraft supply stores.

Placing de-/anti-icing fluid close to a high heat source, such as a Janitrol heater, creates a fire hazard and is not acceptable. If no such space is available, then sufficient quantities should be made available at away bases.

After de-icing, if anti-icing is required, spray on the correct amount, usually between 1 mm and 3 mm. Do not coat the critical surfaces with too thick a layer, as this may cause aerodynamic problems after takeoff; too thin a layer, and the fluid may not achieve the specified HOT values. The fluid manufacturer will have instructions on proper coverage.

Using a small sprayer to de-ice a larger aircraft, such as a business jet, is not practical. The amount of fluid required to correctly apply de-icing fluid can be quite large. Typically, a small business jet requires 45 to 60 litres (12 to 15 U.S. gallons) or more to de-ice, depending on the amount of frozen contamination to be removed. Using a hand sprayer to apply anti-icing fluid is not recommended either because the time involved would erode valuable HOT. Remember, the HOT starts at the commencement of the anti-icing procedure.

The fluids that have been developed are called Type I, II, III, and IV.

Type I fluid was developed initially, and is used primarily, as a heated de-icing medium. It is also used by smaller aircraft (rotation speeds over 60 kt and ground acceleration times exceeding 16 seconds), for de-/anti-icing; however, the protection is for a short period of time. See When in Doubt...Small and Large Aircraft-Aircraft Critical Surface Contamination Training for Aircrew and Groundcrew (TP 10643), Chapter 3, paragraph 42, "Low Speed Test."

Type II fluid was developed as an anti-icing protection, and is still in use today. The thickening properties of this fluid extend HOT compared to Type I fluid; however, its use is intended for aircraft with rotation speeds in excess of 100 kt and ground acceleration times greater than 23 seconds. See When in Doubt...Small and Large Aircraft-Aircraft Critical Surface Contamination Training for Aircrew and Groundcrew (TP 10643), Chapter 3, paragraph 41, "High Speed Test."

Type III fluid was developed as an anti-icing fluid similar to Type II fluid; however, its use is intended for aircraft with rotation speeds over 60 kt and ground acceleration times exceeding 16 seconds.

Type IV fluid was developed as an anti-icing fluid similar to Type II fluid but with greater HOT qualities. Its use is also for aircraft with rotation speeds in excess of 100 kt and ground acceleration times greater than 23 seconds.

When spraying to de-/anti-ice your aircraft, confirm that the fluid being used is appropriate for your aircraft type. A check in the pilots operating handbook (POH), aircraft flight manual (AFM), or with the manufacturer, will tell you which fluid is appropriate for your aircraft. Be sure to follow the instructions. Generally, smaller aircraft are limited to Type I fluid. A Type III fluid has been developed for smaller aircraft; however, it is only available in limited regions. It is anticipated that this fluid will be more widely available in the next few years. The advantage of Type III fluid is that it contains some thickeners to increase HOT. Be sure your aircraft manufacturer recommends the use of Type III fluid before you use it.

Some pilots believe that any fluid can be used on an aircraft. This is not true. Do not use Type II or Type IV fluid on an aircraft that this fluid is not approved for. De-/anti-icing fluids are only required until the aircraft becomes airborne, after which the on-board de-/antiicing systems operate. The rotation speed of an aircraft is important, as this determines which de-/anti-icing fluid should be used. Serious aerodynamic consequences can result from incorrect fluid use. The result could be disastrous, as the fluid will not shear off (blow off) on the take-off run, which may cause aerodynamic problems just after takeoff.

Remember, Canadian Aviation Regulation (CAR) 602.11(4) states (for non-airline operations):

Where conditions are such that frost, ice or snow may reasonably be expected to adhere to the aircraft, no person shall conduct or attempt to conduct a takeoff in an aircraft unless

  1. for aircraft that are not operated under Subpart 5 of Part VII,
    1. the aircraft has been inspected immediately prior to takeoff to determine whether any frost, ice or snow is adhering to any of its critical surfaces, or
    2. the operator has established an aircraft inspection program in accordance with the Operating and Flight Rules, Standards, and the dispatch and takeoff of the aircraft are in accordance with that program.

If you use a holdover table for guidance, use the correct table for the fluid being used. There are some differences between fluids produced, and the holdover tables address specific fluids. Using the incorrect holdover table will lead to incorrect values for the integrity of the fluid and your HOT.

In certain cases, where cold snow is falling on a cold wing and definitely not accumulating or adhering to the critical surfaces, it may not be necessary to de-/anti-ice; however, be prudent and double-check the critical surfaces to ensure that no contamination is adhering or accumulating on them. This can only be done on the walk-around while conducting a tactile (touch) inspection of the surfaces. Be extra careful at night or during times where visibility is restricted, as visual detection can be impossible. Tactile inspection is the only positive method to ascertain the condition of the critical surfaces.

Various methods to remove contamination were discussed in the ASL 3/2005 article, so readers may want to read it again. When removing frozen contamination from the critical surfaces, also ensure that all elevator, aileron, and flap, etc., hinge lines are clean to avoid these surfaces refreezing after takeoff.


Anti-icing fluids (Types II and IV) have been known to remain in aerodynamically quiet areas such as elevator, aileron, and flap, etc., hinge lines after takeoff. They may re-freeze while airborne, causing control restrictions or flutter. Be aware of the manufacturer's recommendations to inspect and clean these areas after anti-icing to ensure no fluid remains trapped. To date, no re-freezing problems have been recorded with Type I fluids.

Active frost

Active frost normally occurs at night when aircraft surfaces are at or below freezing (0°C) AND at or below the dew point. Therefore, expect active frost conditions when the temperature-dew point spread is small, within about
2°C, and the dew point and aircraft temperatures are below freezing. Active frost will actively grow in mass and thickness, and will continue to form after being removed; whereas inactive frost, such as hoar frost, can be removed and normally will not form again.

The above conditions, combined with the VFR conditions of clear sky and calm winds, enhance the chance for active frost. If you choose to take off in these conditions, you will have to de-ice with Type I fluid, and anti-ice with Type II or Type IV. Owners of smaller aircraft types, unable to use Type II or IV fluid, can de-ice with heated Type I fluid, then reapply Type I fluid as an "anti-ice" a second time to create a fresh layer of protection and some additional HOT.

The National Aeronautics and Space Administration (NASA) Glenn Research Centre in Cleveland, Ohio, has two excellent products on aircraft ground and in-flight icing entitled, A Pilot's Guide to Ground Icing and A Pilot's Guide to In-Flight Icing on their Web site located at:

section on de-/anti-icing general aviation aircraft.

Flying a smaller aircraft type in the winter can provide a great opportunity to fly in smooth, clear weather conditions; however, these conditions can deteriorate quickly.

Use all the resources available to you-Internet, airport personnel or local weather-to determine ground-icing factors. Sometimes the best decision is "don't go"...your life may depend on it.

When you push the weather and get into trouble, remember who put you there.

How Much is Too Much? Test Your Knowledge of Operations During Icing Conditions
by Captain Robert Kostecka, Civil Aviation Safety Inspector, Foreign Inspection, International Aviation, Civil Aviation, Transport Canada

In Canada, flying during the winter brings many challenges. Everyone who has driven a car on a slushy highway-or walked on an ice-covered sidewalk-knows that we need to be extra careful when weather conditions are poor. In addition to the problems of runway contamination, we also need to ensure that the aircraft's critical surfaces are not contaminated with frost, ice or snow.

For years, most pilots have understood that visible ice contamination on a wing can cause severe aerodynamic and control penalties. The continued occurrence of icing-related accidents makes it apparent that some pilots do not recognize that even minute amounts of ice adhering to a wing can have disastrous consequences. As far as frost, ice or snow adhering to the aircraft's critical surfaces is concerned, no amount is acceptable. Contamination makes no distinction between large aircraft, small aircraft or helicopters. The performance penalties and dangers are just as real. As winter approaches, it is a good idea to take a few moments to review flight operations during icing conditions. To help you prepare for this winter's challenges, here are a few questions that will illustrate some of what you need to know.

The questions have been divided into two groups. Part A consists of general knowledge questions that are applicable to all pilots. The questions in Part B are intended for the operators of larger and more complex aircraft that operate in ground icing conditions.

For your convenience, references and associated links have been provided. The answers to these questions can be found below.

TP 10643 When in Doubt...Small and Large Aircraft-
Aircraft Critical Surface Contamination Training for Aircrew and Groundcrew

Canadian Aviation Regulations (CARs)

NTSB Advisory-Alert to Pilots: Wing Upper Surface Ice Accumulation 05.htm

Part A: General Knowledge

1. Which of the following accidents was caused by ice on the aircraft's critical surfaces?

  1. January 13, 1982: An Air Florida Boeing 737-200 crashed into the 14th St. Bridge and the Potomac River, and sank shortly after taking off from Washington National Airport. There were 74 fatalities.
  2. March 10, 1989: An Air Ontario F28 crashed during takeoff from Dryden, Ont. There were 24 fatalities. (This crash resulted in a major investigation that led to the Air Regulations changes that are in place today.)
  3. January 4, 2002: A Canadair Challenger crashed during takeoff from Birmingham, England. All 5 on board were killed.
  4. All of the above.
Ref.: TP 10643 Chapter 1, "Air Law, The Clean Aircraft Concept"

2. For the purpose of aircraft icing, which of the following are considered to be the aircraft's "critical surfaces"?

  1. The wings, rotors and propellers.
  2. Control surfaces, horizontal stabilizers, vertical stabilizers or any other stabilizing surface of an aircraft.
  3. In the case of an aircraft that has rear-mounted engines, the upper surface of the aircraft's fuselage.
  4. All of the above.
Ref.: CAR 602.11-Aircraft Icing

3. It is a bright, crisp, clear winter day, and you are the pilot of a light training aircraft. You and your passengers are anxious to get underway. During the walk-around, you notice that there is a thin layer of frost on the upper surface of the wings.

Which of the following statements is correct?

  1. A thin layer of frost may not be a problem. This is a matter of judgement and airmanship. Takeoff is possible in this situation. The Canadian Aviation Regulations (CARs) only prohibit takeoff when the amount of ice, snow or frost will adversely affect safety.
  2. The CARs prohibit persons from conducting or attempting to conduct a takeoff in an aircraft that has frost, ice or snow adhering to any of its critical surfaces such as wings and propellers. This is called the "clean aircraft concept."
  3. Research results have shown that fine particles of frost or ice the size of a grain of table salt and distributed as sparsely as one per square centimetre over an airplane wing's upper surface can destroy enough lift to prevent that airplane from taking off.
  4. Both b) and c) are correct.
Ref.: CAR 602.11-Aircraft Icing
TP 10643 Chapter 1, "Air Law, The Clean Aircraft Concept"
NTSB Advisory- Alert to Pilots: Wing Upper Surface Ice Accumulation

4. Which of the following statements concerning frost is correct?

  1. Research results have shown that fine particles of frost or ice the size of a grain of table salt and distributed as sparsely as one per square centimetre over an airplane wing's upper surface can destroy enough lift to prevent that airplane from taking off.
  2. CAR 602.11(3) states: "...a person may conduct a takeoff in an aircraft that has frost adhering to the underside of its wings that is caused by cold-soaked fuel, if the takeoff is conducted in accordance with the aircraft manufacturer's instructions for takeoff under those conditions."
  3. Both a) and b) above are correct.
  4. None of the above is correct.
Ref.: NTSB Advisory-Alert to Pilots: Wing Upper Surface Ice Accumulation
TP 10643 Chapter 2, "Theory and Aircraft Performance- Frozen Contaminants"
CAR 602.11(3)

5. You are travelling as a passenger on an airliner. Your flight has been delayed several hours because of a mechanical problem. The passengers are quite annoyed. Eventually, the airline has another aircraft towed to the gate.

As you take your seat, you notice that there is frost on the wings. The captain welcomes everyone aboard and says that because there is no traffic ahead on the taxiway, he expects to be airborne very quickly. He makes no mention of de-icing. You don't feel comfortable about the frost.

With respect to this situation, which of the following statements is correct?

  1. In this situation, you should keep quiet and trust that everyone is doing their job. If the crew thought that de-icing was necessary they would do it. This is not your concern.
  2. You should tell a flight attendant that there is frost on the wings. If a flight attendant observes that there is frost, ice or snow adhering to the wings of the aircraft, the CARs require that they must immediately report that observation to the pilot-in-command. The pilot-in- command or a flight crew member designated by the pilot-in-command must inspect the wings of the aircraft before takeoff.
  3. Before an aircraft is de-iced or anti-iced, the pilot-incommand of the aircraft must ensure that the crew members and passengers are informed of the decision to do so.
  4. Both b) and c) are correct.
Ref.: CAR 602.11(6)
CAR 602.11(7)
Aviation Safety Letter 1/2004

Part B: For Operators of Aircraft That Operate in Ground Icing Conditions

1. With respect to holdover times, which of the following statements is true?

  1. Holdover time tables are referred to as holdover time"guidelines" because this term more appropriately represents their function in providing guidance to flight crew and the need for the flight crew to use judgment in their interpretation.
  2. Holdover time guidelines provide an estimate of the length of time anti-icing fluids will be effective.
  3. The actual time that a fluid is effective can be less than that published in the holdover time guidelines. Factors including strong winds and jet blast may reduce holdover times.
  4. All of the above statements are true.
Ref.: TP 10643 Chapter 2, "Theory and Aircraft Performance- Frozen Contaminants"

2. With respect to holdover times, which of the following statements is true?

  1. Aircraft anti-icing fluid holdover times have not been evaluated under moderate and heavy freezing rain conditions.
  2. The capability of anti-icing fluid to tolerate a heavy snowfall rate has not been evaluated; therefore holdover times for heavy snow conditions have not been generated.
  3. Both a) and b) above are true.
  4. None of the above is true.
Ref.: TP 10643 Chapter 2, "Theory and Aircraft Performance-Frozen Contaminants"

3. With respect to SAE Type I (de-ice) fluids, which of the following statements are correct?

  1. SAE Type I (orange) fluids are used for de-icing or anti-icing, but provide very limited anti-icing protection.
  2. It is the heat contained by the Type I (de-ice) fluid and the hydraulic forces that remove the frozen contaminants.
  3. Extra vigilance is required by flight crews when conducting operations after spraying with Type I fluids only. Flash freeze over (fluid failure) can occur in a very short period of time after the holdover time expires, even in very light precipitation conditions. This results in a contaminated critical surface and an unsafe condition for flight.
  4. All of the above.
Ref.: TP 10643 Chapter 3, "De-icing/Anti-icing Fluids-Fluid Properties"

4. With respect to SAE Type IV fluids, which of the following statements is correct?

  1. Type IV anti-icing fluids should only be used on aircraft with rotation speeds (Vr) above 100 kt.
  2. Type IV anti-icing fluid is dyed emerald green to provide for application of a more consistent layer of fluid to the aircraft and to reduce the likelihood that fluid will be mistaken for ice.
  3. Both a) and b) are correct
  4. None of the above.
Ref.: TP 10643 Chapter 3, "De-icing/Anti-icing Fluids-Fluid Properties"

5. An exemption to CARs 602.11(1) and (2) has been issued. The purpose of this exemption is to permit Canadian air operators and foreign air operators in Canada, utilizing aircraft with engines mounted on the rear of the fuselage, to conduct a takeoff with hoar-frost on the fuselage only, after it has been determined that no other contamination is adhering to the fuselage.

What are the conditions of this exemption?

  1. Hoar-frost shall be the only acceptable contaminant on the fuselage of aircraft with engines mounted on the rear fuselage.
  2. Prior to conducting a takeoff, the operator shall ensure that the hoar-frost is not mixed with other contaminants such as ice or snow. If any other contaminant or contaminants are on the fuselage, the operator shall de-ice the entire fuselage.
  3. A copy of this exemption shall be attached to the aircraft de-icing/anti-icing procedures in the operator's manual.
  4. All of the above.
Ref.: TP 10643 Chapter 1, "Air Law, The Clean Aircraft Concept"

Answers to "How Much is Too Much?" Quiz

Part A: (1) d, (2) d, (3) d, (4) c, (5) d. Part B: (1) d, (2) c, (3) d, (4) c, (5) d.

There is no such thing as a little ice. In airline operations where large numbers of aircraft are dispatched, the process of assuring that each flight will be safe must be a team effort. In smaller commercial and in private operations, the pilot may have to perform all the functions. In all cases, the pilot-in-command is ultimately responsible for ensuring that the aircraft is in a condition for safe flight. If the pilot cannot confirm that the aircraft's critical surfaces are free of contamination, takeoff must not be attempted.

2006–2007 Ground Icing Operations Update

In July 2006, the Winter 2006–200 Holdover Time (HOT) Guidelines were published by Transport Canada. As per previous years, TP 14052, Guidelines for Aircraft Ground Icing Operations, should be used in conjunction with the HOT Guidelines. Both documents are available for download at the following Transport Canada Web site: If you have any questions or comments regarding the above, please contact Doug Ingold at

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