The loss of performance due to ice or snow contamination of leading edges and wing upper surfaces, particularly during the take-off phase of flight where high angles of attack are present, has been known to aircraft manufacturers, regulatory and accident investigation authorities, and operators for many years.

For almost four decades, United States Federal Aviation Regulations have prohibited take-off of aircraft when frost, snow, or ice adheres to the wings, propellers, or control surfaces of an aircraft. These regulations are known collectively as the "clean wing regulations." Additionally, in 1982 the Federal Aviation Administration issued Advisory Circular (AC) 20-117 to address frequent misconceptions concerning the effects of slight surface roughness on aircraft performance caused by ice accumulation. The circular outlines the aerodynamic principles of changes in lift and drag due to wing surface roughness and emphasizes that take-off is not to be attempted unless it has been confirmed that all critical components are free of adhering snow, frost, or other ice formations. AC 20-117 states that close inspection is the only known method of ensuring clean wings and flight control surfaces before flight.

In Canada, legislation contained in Air Navigation Order Series VII, Number 2 governing air carrier operations using large aircraft, repeats the U.S. clean wing regulations, and a section of the Aeronautical Information Publication cautions pilots against the hazards of attempting flight with wing or control surfaces contaminated by snow, ice, or frost.

In spite of existing regulations and promotional material, numerous aircraft occurrences bear witness to the fact that flight is sometimes attempted when wing surface contamination due to ice, snow, or frost is present. Accident investigations and analyses of aircraft occurrences concerning aircraft such as the Boeing 737-200 series, the McDonnell-Douglas DC-9 Series 10, and this occurrence involving a Douglas DC-8-63 series aircraft all confirm that leading edge and wing surface contamination due to ice and snow can degrade aircraft performance during the take-off phase of flight to the point where there is little to no margin of safety. This loss of performance is particularly severe in aircraft like the DC-8 which do not have leading edge devices to augment lift and to allow the aircraft to attain a higher angle of attack before the wings stall.

The Board has no doubt that flight crews understand the aerodynamic principles concerning loss of performance due to readily visible amounts of ice, snow, or frost contamination of leading edges. However, the Board believes that many flight crews do not fully comprehend the magnitude of performance penalties attributable to small amounts of ice contamination. Aircraft operating manuals and other aircraft performance documents contain little or no information on the magnitude of performance penalties possible with relatively minor amounts of surface roughness. Therefore, the CASB recommends that:

The Department of Transport initiate a national safety campaign to ensure that all pilots are aware of the potential consequences of attempting take-off with even minor amounts of contamination on the wings.

CASB 88-07

Wing Ice Detection

The Board notes that Canadian companies operating DC-9 aircraft currently use only the DC-9-30 series, which are equipped with leading edge high lift devices and which are thus less susceptible to performance degradation from wing ice contamination. However, the deficiency identified by the NTSB is applicable to DC-8 aircraft which are operated in Canada. The Board believes that the circumstances of the accidents involving the DC-9-10 at Denver and the DC-8 at Gander confirm the need for Canadian flight crew operating aircraft not equipped with wing leading edge high lift devices to be able to detect the presence of ice on the wings. Accordingly, the CASB recommends that:

As a consequence of an investigation into an accident of a McDonnell-Douglas DC-9-10 series aircraft at Denver Colorado on 15 November 1987, the NTSB recently issued two recommendations to the FAA to address the hazards of conducting a take-off in the DC-9-10 with undetected ice on the upper wing surfaces. The recommendations call for operators of this aircraft type, which is not equipped with wing leading edge high lift devices, to establish detailed procedures for detecting upper wing ice prior to take-off and, until such time as the procedures have been implemented, to anti-ice these aircraft with maximum effective strength glycol solution when icing conditions exist.

The Board notes that Canadian companies operating DC-9 aircraft currently use only the DC-9-30 series, which are equipped with leading edge high lift devices and which are thus less susceptible to performance degradation from wing ice contamination. However, the deficiency identified by the NTSB is applicable to DC-8 aircraft which are operated in Canada. The Board believes that the circumstances of the accidents involving the DC-9-10 at Denver and the DC-8 at Gander confirm the need for Canadian flight crew operating aircraft not equipped with wing leading edge high lift devices to be able to detect the presence of ice on the wings. Accordingly, the CASB recommends that:

The CASB believes that the lack of useful cockpit voice recorder (CVR) information in com bination with the inaccurate and minimal flight data recorder (FDR) information provided by five-parameter foil-type flight recorders contributed significantly to the difficulty in determining the causes and factors that led to this accident. In particular, the Board's understanding of any contributing night crew human factors is incomplete. The Board is pleased that regulatory revisions to improve the capabilities of FDRs, in keeping with the International Civil Aviation Organization (ICAO) standards and recommended practices, have been undertaken or proposed in both Canada and the United States; however, the Board believes that easily implementable procedures ensuring the serviceability of CVRs should be introduced.

For a number of years, CVRs have had the capability for flight crews to test the cockpit area microphone channel; this feature is pan of the Technical Standards Order requirement for such equipment. This self-test feature allows flight crews to functionally check the cockpit area microphone channel before flight and quickly detect an unserviceability. Canadian and U.S. regulations specify that flights must be conducted with a serviceable and functioning CVR. However, there are no prescribed procedures with respect to the nature or frequency of CVR tests. It is understood that some operators' procedures include a test prior to each flight, some require only one test daily, and others include tests on a less frequent schedule. As a result, there is potential for unserviceabilities to remain undetected through a number of flights conducted between functional tests.

The Board believes that, in the event of an occurrence, recorded cockpit communications can be vitally important in understanding the sequence of events and in assessing the influence of human factors. Accordingly, the CASB recommends that:

The Department of Transport review the procedures currently m place with respect to functional checks of cockpit voice recorders with a view to ensuring that the serviceability of the equipment is being tested adequately.

The National Transponation Safety Board consider seeking parallel action in the United States to that outlined for Canada in CASB 88-09.

The CASB accident investigation into this occurrence determined that, in the 11 days leading up to the accident, the flight crew had exceeded specified flight-time limitations twice and had less than minimum crew rest on at least one occasion. Thus, there was a potential for the development of fatigue, with its concomitant potential for adversely affecting pilot judgement and crew coordination. Furthemmore, on the day of the accident, the crew's planned ferry flight to Oakland, California after the flight to Fon Campbell would have resulted in the accumulation of about 15 flight hours in less than a 24-hour period and a duty period of almost 20 hours. Nevertheless, this would not have contravened U.S. regulations.

In 1986, the CASB identified several safety deficiencies in current Canadian legislation regarding maximum crew-flight and duty-time limitations and minimum crew-rest provisions. Three of six related recommendations issued by the Board to Transport Canada suggested that there be more stringent regulations goveming crew-duty hours and crew-rest cycles for crews of large transoort-category aircraft.

The Board notes that, in general, the U.S. FARs prescribe more stringent controls to prevent fatigue-related accidents than are applicable in Canada today. However, while FAR Pan 121 (applicable to air carriers and commercial operators of large aircraft) specifies flight-time limitations and minimum crew-rest periods, these restrictions do not always apply. Ferry flights and other non-revenue operations can be conducted under the provisions of FAR Part 91 (general operating and flight rules) which do not include any limitations on flight time nor prescribe minimum crew-rest periods. The Board believes that the flight crews of FAR Part 121 air carriers require the same degree of vigilance, judge nent, and ability to react whether they are conducting a revenue-generating or non-revenue operation. Therefore, the CASB recommends that:

The National Transponation Safety Board consider recommending a change in U.S. Federal Aviation Regulations such that the flight-time, duty-time, and crew-rest provisions of FAR Part 121 would apply to all operations of Part 121 air carriers, including non-revenue flights.

CASB 88-11