Clean Aircraft Concept

The continuing number of accidents involving all types and classes of aircraft indicates that misconceptions exist regarding the effect on performance of frost, snow or ice accumulation on aircraft.

Most commercial transport aircraft, as well as some other aircraft types, have demonstrated some capability to fly in icing conditions and have been so certified. This capacity is provided by installing de-icing or anti-icing equipment on or in critical areas of equipment, such as the leading edges of the wings and empennage, engine cowls, compressor inlets, propellers, stall warning devices, windshields and pitots. However, this equipment does not provide any means of de-icing or anti-icing the wings or empennage of an aircraft that is on the ground.

Where frost, ice or snow may reasonably be expected to adhere to the aircraft, the Canadian Aviation Regulations require that an inspection or inspections be made before takeoff or attempted takeoff. The type and minimum number of inspections is indicated by the regulations, and depends on whether or not the operator has an approved Operator’s Ground Icing Operations Program using the Ground Icing Operations Standard as specified in CAR 622.11 – Operating and Flight Rules Standards.

The reasons for the regulations are straightforward. The degradation in aircraft performance and changes in flight characteristics when frozen contaminants are present are wide ranging and unpredictable. Contamination makes no distinction between large aircraft, small aircraft or helicopters, the performance penalites and dangers are just as real.

The significance of these effects are such that takeoff should not be attempted unless the pilot-in-command has determined, as required by the CARs, that frost ice or snow contamination is not adhering to any aircraft critical surfaces.

Critical surfaces of an aircraft mean the wings, control surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilizing surface of an aircraft which, in the case of an aircraft that has rear-mounted engines, includes the upper surface of its fuselage.

Flight safety during ground operations in conditions conducive to frost, ice or snow contamination requires a knowledge of:

Adverse effects of frost, ice or snow on aircraft performance and flight characteristics, which are generally reflected in the form of decreased thrust, decreased lift, increased drag, increased stall speed, trim changes, altered stall characteristics and handling qualities.
Various procedures available for aircraft ground de-icing and anti-icing, and the capabilities and limitations of these procedures in various weather conditions, including the use and effectiveness of freezing point depressant (FPD) fluids
Holdover time, which is the estimated time that an application of an approved de-icing/anti-icing fluid is effective in preventing frost, ice, or snow from adhering to treated surfaces. Holdover time is calculated as beginning at the start of the final application of an approved de-icing/anti-icing fluid and as expiring when the fluid is no longer effective. The fluid is no longer effective when its ability to absorb more precipitation has been exceeded. This produces a visible surface build-up of contamination.

CARs prohibit takeoff when frost, ice or snow is adhering to any critical surface of the aircraft. This is referred to as “The Clean Aircraft Concept”.

It is imperative that takeoff not be attempted in any aircraft unless the pilot-in-command has determined that all critical components of the aircraft are free of frost, ice or snow contamination. This requirement may be met if the pilot-in-command obtains verification from properly trained and qualified personnel that the aircraft is ready for flight.