Appendix A: Background to Legal and Regulatory Positions
1. FAA and NTSB Legal Positions
1.1. The NTSB has upheld for many years a legal definition of “known icing conditions” that refers not to ice currently accreting, but to the information available to the pilot before and during the flight, information which may include forecasts (Regulatory Reference 3.2.e):
“We do not construe the adjective 'known' to mean that there must be a near certainty that icing will occur, such as might be established by pilot reports. Rather we take the entire phrase to mean that icing conditions are being reported or forecast in reports which are known to a pilot, or of which he should reasonably be aware.”
1.2. This has been further reinforced by the NTSB in Regulatory Reference 3.2.f, where it is stated that to construe a restriction on flight in known icing conditions as not being a limitation to fly in forecast icing conditions renders the limitation meaningless and has little effect as a safety measure.
1.3. When weighing between reports and forecasts, the NTSB has further ruled that it is not at a pilot’s discretion to “pick and choose” between a forecast and anecdotal PIREPs (Regulatory Reference 3.2.g):
- “While PIREPs are valuable in planning (and are used in developing the SIGMETs), they are only one factor to consider. We, thus, do not agree with respondent's claim that a pilot report will establish the absence of icing with "near certainty."; and
- “For similar reasons, pilots may not, in the face of icing forecasts for an area, reasonably rely on anecdotal information regarding freezing levels. Weather reporting is not the exact science that respondent's theory would have us assume.”
1.4. The FAA has expressed a similar position to the NTSB (at Regulatory Reference 3.2.h) with respect to forecast icing being known icing. It also provides a rationale that illustrates the Regulator’s intention to preventively keep aircraft away from icing, not reactively, given the severity of the icing hazard to aircraft:
- “If the composite information indicates to a reasonable and prudent pilot that he or she will be operating the aircraft under conditions that will cause ice to adhere to the aircraft along the proposed route and altitude of flight, then known icing conditions likely exist”; and
- “Flight in known icing conditions by an aircraft not approved and equipped for such operations presents a significant safety hazard. By the time the ice adheres to the aircraft (or more appropriately is observed to adhere to the visible parts of the aircraft), it may be too late for the pilot to take actions to assure the further safety of the flight”.
2. Regulatory Positions
2.1. The FAA clarifies that icing conditions are those conducive to icing. It further provides a quantitative means to estimate them, in Regulatory Reference 3.2.i:
“After October 21, 2013, no person may operate an airplane with a certificated maximum takeoff weight less than 60,000 pounds in conditions conducive to airframe icing unless it complies with this section. As used in this section, the phrase “conditions conducive to airframe icing” means visible moisture at or below a static air temperature of 5 °C or a total air temperature of 10 °C, unless the approved Airplane Flight Manual provides another definition.”
2.2. European Regulations at Regulatory Reference 3.2.j stress that flight through icing conditions, known icing conditions and forecast icing conditions shall only be allowed in an icing certified aircraft. They also stress that all reasonably available information (which would include forecasts) shall be used. The relevant paragraphs are as follows:
“ 2. Flight preparation
2.a. A flight must not be commenced unless it has ascertained by every reasonable means available that all the following conditions are complied with;
[…]
2.a.5. In case of flight into known or expected icing conditions, the aircraft must be certified, equipped and/or treated to operate safely in such conditions.”
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