Chapter 1 - Air Law, The Clean Aircraft Concept

1.  As demonstrated in the above examples, the degradation in aircraft performance and changes to the 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 penalties and dangers are just as real.

2.  Frost, ice or snow on critical surfaces of an aircraft such as wings, propellers and stabilizers can have a significant impact on the operation of an aircraft. The aircraft can be affected in two ways.

  • The additional weight of the ice or snow adds to the total weight of the aircraft, increasing the lift required for the aircraft to take off.
     
  • The formation of frost, ice or snow also changes the airflow over the wing, reducing the overall lift a wing can produce.

3.  On March 10, 1989 at Dryden, Ontario an Air Ontario Fokker F-28 MK 1000 crashed off the end of the runway on departure. Twenty-one of the 65 passengers and three of the four crew members (including the Captain, First Officer and one Flight Attendant) on board died as a result of the crash. The aircraft was destroyed in the post crash fire.

4.  The Commission of Inquiry into this accident, concluded that information regarding the operation of aircraft on a wet and contaminated runway must be made available to persons at all levels of flight operations.

5.  The significance of these effects are such that no person shall conduct or attempt to conduct a take-off in an aircraft that has frost, ice or snow adhering to any of its critical surfaces. The Canadian Aviation Regulations (CARs) prohibit persons from conducting or attempting to conduct a take-off in an aircraft that has frost, ice or snow adhering to any of its critical surfaces such as wings and propellers. Therefore, if the Pilot-in-Command (PIC) cannot confirm that the aircraft is "clean", takeoff must not be attempted until confirmation is obtained that the aircraft is free of frozen contaminants. This is called the "Clean Aircraft Concept."

6.  Where frost, ice or snow may reasonably be expected to adhere to the aircraft, the CARs require that an inspection or inspections shall be made before take-off or attempted take-off. The type and minimum number of inspections indicated by the regulations, depends on whether or not the operator has an approved Ground Icing Operations Program using the Ground Icing Operations Standards as specified in the General Operating and Flight Rules, 622.11 (GOFR 622.11)

7.  There are strict regulations in Canada governing the removal of ice, frost and snow (deicing) and preventing their accumulation on aircraft (anti-icing) prior to departure. Air operators are responsible for having deicing and anti-icing procedures in place to comply with Canadian Aviation Regulations. An inspection by delegated company personnel or the Pilot-in-Command (PIC) must be conducted immediately prior to take-off to make sure that no frost, ice or snow is present. Transport Canada enforces its deicing and anti-icing regulations through a number of means, including a comprehensive monitoring, inspections and audits program.

8.  The Clean Aircraft Concept is essential to the maintenance of flight safety. In all aviation operations, the PIC has the ultimate responsibility to determine if the aircraft is in a condition for safe flight. However, flight crewmembers, ground or maintenance personnel, or any other operational personnel shall report frozen contamination adhering to the aircraft, to the PIC.

9.  It is imperative that take-off not be attempted on any aircraft unless the PIC has determined that all critical surfaces of the aircraft are free of frost, ice or snow contamination. This requirement may be met if the PIC obtains verification from properly trained and qualified personnel that the aircraft is ready for flight. Aircraft without rear-mounted engines are permitted to take-off with "Hoar frost" (see glossary) adhering to the fuselage only, provided this is approved in the aircraft manufacturers instructions.

10.  However, a Notice of Proposed Amendment (NPA) to the pertinent sections of CAR 602.11 and GOFR 622.11 has been submitted which, under specified conditions, would permit Canadian Air Operators and Foreign Air Operators in Canada operating aircraft with rear-mounted engines to conduct a takeoff with hoar-frost on the fuselage. At the time of printing, this NPA had not been approved.

11.  In the meantime, 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.

12.  The exemption is subject to the following conditions:

  • Hoar-frost shall be the only acceptable contaminant on the fuselage, of aircraft with engines mounted on the rear fuselage.
     
  • 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.
     
  • A copy of this exemption shall be attached to the Aircraft Deicing/Anti-icing Procedures in the Operator's Manual.

13.  The CAR's require that all personnel involved in aircraft operations shall have initial and annual personnel directly participating in aircraft operations such as, deicing crews and baggage handlers. Any person observing frozen contamination on the aircraft critical surfaces shall report this immediately to the PIC.

14.  This combination of reduced lift and increased weight can have crucial safety consequences even with small amounts of ice or snow. Test data indicates that during takeoff, frost, ice or snow formations having a thickness and surface roughness similar to medium or coarse sandpaper, on the leading edge and upper surface of a wing, can reduce wing lift by as much as 30% and increase drag by 40%. Even small amounts of contamination such as this have caused and continue to cause aircraft accidents, which result in substantial damage and loss of life. A significant part of the loss of lift can be attributed to leading edge contamination. The changes in lift and drag significantly increase stall speed, reduce controllability and alter aircraft flight characteristics. Thicker or rougher frozen contaminants can have increasing effects on lift, drag, stall speed, stability and control.

15.  The removal of the contaminants prior to flight operations is accomplished through the application of a heated deicing fluid that melts the ice and removes it from the aircraft. In addition, an ice-preventive agent (anti-icing fluid) may be applied to critical surfaces prior to take-off, to prevent the accumulation of ice on critical surfaces. Aircraft that are approved for flight into known icing conditions are equipped with devices that, while the aircraft is in flight, either break up and remove ice on critical surfaces (de-ice boots) or prevent the accumulation of ice on critical surfaces (heated wing leading edge devices).

16.  Also, a phenomenon, called "cold soaking" (discussed later), can form clear ice or frost on the wings. Under these circumstances, take-off is permitted only with the aircraft manufacturers approved instructions. In most cases, these approved instructions will specify a maximum allowable thickness for the contamination and usually limit its presence to the underside of the wing.

17.  There is no such thing as a little ice.

When in Doubt... Ask, Investigate, Check!