CL650/Operations Reference/Operations in Icing Conditions

This information is simplified for simulation.

Icing conditions exist at a Total Air Temperature (TAT) of 10 °C (50 °F) or below with visible moisture in any form (such as clouds, rain, snow, sleet, or ice crystals), except when Static Air Temperature (SAT) is −40 °C (−40 °F) or below.

SAT −40 °C ≤ ICING RANGE ≤ TAT 10 °C

Icing on the Ground

The Challenger is equipped with a cowl anti-ice system to protect the engines and nacelles, and a wing anti-ice system to protect the wings from ice accretion in flight. It must be remembered that the wing anti-ice system will only protect the aircraft in flight. Snow and ice buildup on the ground must be removed using the simulated de-ice/anti-ice service. Request de-icing either via the FBO or by calling the de-ice crew on VHF frequency 136.925 MHz (select the frequency and then operate the R/T switch on the audio control panel). The de-ice crew will offer to either de-ice the aircraft, or de-ice and then anti-ice the aircraft.

“De-ice only” will remove existing snow and ice from the aircraft, but will not provide any longer term protection against further ice accumulation. This is most suitable on a cold, clear day with no active precipitation after overnight frost. “De-ice and anti-ice” will begin with a de-ice treatment (as above) to remove any contamination, and then a second fluid treatment will begin to provide protection against further contamination for a certain period of time, referred to as the “holdover time.” Holdover time begins at the start of the second treatment, and ends depending on fluid type and precipitation intensity. The FAA provides publicly accessible holdover tables, linked below. De-icing is performed with Type I (1) fluid, while anti-icing is performed with Type II (2) or Type IV (4) fluid, with Type IV being the default if no preference is given in the FBO.

Fluid Type	Color	Example Holdover (Snow)	Example Holdover (Rain on cold wing)
I (1)	Red / Orange	5 minutes	2–5  minutes
II (2)	Straw	20 minutes	4–25 minutes
IV (4)	Green	35 minutes	9–75 minutes

Source:

It is absolutely vital to ensure the wing is free from contamination before take-off. The Challenger's wings employ a supercritical airfoil, which improves fuel efficiency at high Mach number, but which is particularly susceptible to a reduction in critical stall angle of attack if its leading edge and upper wing surface become contaminated by any ice buildup or foreign object debris (FOD). Supercritical airfoils feature a fairly flat upper wing shape with very little curvature, which spreads the generated low-pressure lifting region over a greater portion of the wing's upper surface. This limits the local acceleration of air in high speed flight, minimizing the formation of shock waves, and reducing high speed drag. This efficiency gain comes at the cost that any shape imperfections of the upper wing surface significantly impact its ability to generate lift at higher angles of attack, reducing the stall margin. Contamination by even small amounts of frost, ice, or snow can lead to a significant reduction in lift and a loss of control during take-off.

Anti-icing fluid is only designed to protect the aircraft up to the point of take-off, and take-off must be carried out within the holdover time. By 100 knots the fluid will have been blown off the wings. It’s important to recognize that were this not the case, the thick anti-ice fluid could also be considered a contaminant that would affect flight safety and performance.

Due to the comparative sensitivity of the Challenger wing to contamination there was the addition of the Supplemental Ground Wing Anti-Ice System (SGWAIS). This provides low temperature ice protection on the ground for the wing leading edges, and is active whenever the Cowl Anti-Ice system is switched on while the Wing Anti-Ice system remains switched off. This system is designed to maintain the wing leading edges at a relatively low temperature, as a high temperature in the leading edges combined with fluid anti-ice treatment can result in damage to the wing skin as a result of overheating the fluid. It will not protect the wings against active precipitation, and does not improve holdover times.

In addition to the SGWAIS, there is an additional procedure to operate the Wing Anti-Ice system during the final stages of taxi in order to ensure there is no residual ice or frost on the leading edges. This procedure must not be carried out if the aircraft has been treated with anti-ice fluid. When taxiing with an Outside Air Temperature (OAT) of 5 °C or less the Wing Anti-Ice system should be selected to NORM, and should be left selected until a green “WING A/ICE ON” message is shown on the Crew Alerting System (CAS). Should Wing Anti-Ice not be required for take-off, the system can be switched off again. Note: This procedure is required even when not in icing conditions—the only controlling factor is the Outside Air Temperature.

Finally, Wing Anti-Ice must be selected NORM before take-off when the OAT is below 5 °C and visible moisture (clouds, precipitation, wet, or contaminated runway) is present below 400 ft. If the aircraft has not been treated with anti-ice fluid then the system can remain selected NORM after the additional procedure detailed above. If anti-ice fluid has been applied the Wing Anti-Ice system must be selected NORM immediately prior to selecting take-off thrust.

To summarize ground operations in icing conditions:

• Single engine taxiing in icing conditions is not authorized.

• Any contamination on the aircraft must be removed by de-icing treatment before take-off.

• Cowl Anti-Ice must be selected ON during taxi in any icing conditions.

• When the aircraft has not been treated with anti-ice fluid, the Wing Anti-Ice must be selected NORM during the final stages of taxi with OAT is below 5 °C regardless of icing conditions, until a green “WING A/ICE ON” message is shown on the CAS. If not required for take-off it can then be selected OFF.

• Wing Anti-Ice must be selected NORM for take-off when the OAT is below 5 °C and visible moisture in any form is present below 400 ft, or whenever the runway is wet, or with any precipitation.
  • If the aircraft has been treated with anti-ice fluid the Wing Anti-Ice system should be selected NORM immediately before setting take-off thrust.
  • If no fluid treatment has occurred the Wing Anti-Ice system should be selected NORM in the final stages of taxi.

Icing in Flight

Operation of the Cowl Anti-Ice system is as previously described. It must be selected ON whenever flying in icing conditions.

Operation of the Wing Anti-Ice system is more complex. When flying below 22,000 ft the system must be selected NORM whenever flying in icing conditions, regardless of whether or not ice is detected on the airframe. Wing Anti-Ice should also be selected NORM whenever there is any ice detected by the ice detection system. This will indicate with an amber “ICE” shown on the CAS.

To ensure correct operation, check for a green “WING A/ICE ON” on the CAS. In some situations this requires a minimum of 78% N₂. The N₂ gauge will show in amber if 78% is not achieved. Note: The Auto Throttle System (ATS) may need to be disengaged in order to maintain the 78% N₂ minimum. (See Special Performance Approach.)

Finally, to ensure the wing is free from any residual ice, the Wing Anti-Ice system must be selected NORM prior to selecting flaps for approach whenever the TAT is 10 °C or below, regardless of icing conditions. Provided the aircraft remains clear of icing conditions and no ice is detected by the ice detection system, the Wing Anti-Ice can be selected OFF after the WING L HEAT and WING R HEAT indicators show on the anti-ice panel and a green “WING A/ICE ON” message is shown on the CAS.

Further reading

• NASA Aircraft Icing: https://aircrafticing.grc.nasa.gov/
• Aviation Safety Report, N90AG: https://aviation-safety.net/database/record.php?id=20020104-0