Summer is almost upon us in the northern hemisphere, but the FAA is embroiled in two significant icing-related issues: a proposed new rule for when de-ice systems are activated and a new interpretation of the term “known icing.”
The notice of proposed rulemaking (Docket No. FAA-2007-27654) is titled “Activation of Ice Protection” and applies to Part 25 transport-category airplanes. It should be noted that Part 25 airplanes have many fewer icing-related accidents than Part 23 airplanes, yet the FAA has not indicated whether it will propose a similar rule for Part 23 certification.
The proposed new rule would add paragraphs (e) through (h) to FAR 25.1419, which specifies ice-protection requirements for certification of transport-category airplanes. The new paragraphs will require manufacturers to add ice-detection and activation systems or specific procedures for flight crews to identify and recognize the first signs of ice accretion so that they can immediately activate ice-protection systems.
This rule would apply to all phases of flight, and it also would mandate that ice-protection systems operate continuously using an automatic system unless they are equipped with an ice-detection system that tells the crew “each time the ice protection system must be cycled.”
This rule appears to target aircraft whose flight manuals instruct pilots to wait for ice to build to one-quarter to one-half inch before inflating de-ice boots, such as the Cessna Citation series and Beech King Airs. This new rule appears to force manufacturers not to allow pilots to wait for ice to build before activating ice-protection systems, which would also eliminate seemingly contradictory AFM instructions such as those for the Citation 560, which directs pilots to wait for ice to build before inflating the boots except during approach, when they should inflate the boots as soon as ice begins accumulating. The rule would apply only to airplanes certified after the rule becomes final.
The comment period closes July 25. The FAA planned to issue a draft advisory circular that suggests how manufacturers can comply with the new rule, but that AC was not on the FAA Web site as of May 10.
‘Known Icing’ Redefined
In other icing news, the comment period closed recently on an FAA draft letter of interpretation that attempts to clarify the meaning of the term “known icing.” The new draft letter of interpretation was issued after the aviation industry expressed concern to the FAA about a June 2006 letter of interpretation (LOI) by an FAA regional counsel that defined known icing as existing “when visible moisture or high relative humidity combines with temperatures near or below freezing.”
The letter also warned pilots that “flying through clouds at an altitude that is near or below freezing would constitute flight into known icing conditions.”
The FAA’s draft letter of interpretation tries to clarify the issue by defining known icing as follows: “If the composite information indicates to a reasonable and prudent pilot that he or she will encounter visible moisture at freezing or near freezing temperatures and that ice will adhere to the aircraft along the proposed route and altitude of flight, then known icing conditions likely exist.”
In its comments about the draft letter of interpretation, the National Air Transportation Association (NATA) wrote, “This most recent version is an overly restrictive interpretation and does not improve on the flawed 2006 LOI.”
NATA pointed out that there is plenty of guidance about the definition of known icing, found in the Aeronautical Information Manual and Advisory Circulars AC 91-74, AC 00-6A and AC 00-45E:
• Known Icing Conditions: Atmospheric conditions in which the formation of ice is observed or detected in flight.
• Potential Icing Conditions: Atmospheric icing conditions that are typically defined by airframe manufacturers relative to temperature and visible moisture that may result in aircraft ice accretion on the ground or in flight. The potential icing conditions are typically defined in the Airplane Flight Manual or in the Airplane Operation Manual.
• Forecast Icing Conditions: Environmental conditions expected by a National Weather Service or an FAA-approved weather provider to be conducive to the formation of in-flight icing on aircraft.
NATA’s letter went on to say that the draft letter of interpretation “inappropriately mixes three readily discernible concepts: known icing conditions, forecast icing conditions and potential icing conditions. It is the association’s contention that by blending these three concepts the FAA has all but negated the use of the term ‘known icing condition.’”
NATA cited an NTSB civil case (No. 76-4273), in which the Safety Board defined “known icing to mean icing that is known to the pilot.” According to NATA, “Known icing conditions can exist only when ice is actually detected–either by a pilot or an ice detection device.”
The FAA’s use of the phrase “known icing conditions likely exist” in the draft letter of interpretation is particularly troublesome to NATA. “‘Known icing conditions’ either exist or they do not,” the association commented.
“There is either ice on an aircraft, or there is not. There can be no ‘likely’ in this concept, as ‘known icing conditions’ cannot be a subjective determination. Visible moisture and an aircraft surface temperature at or below zero degrees Celsius are two prerequisites for icing, but these two conditions do not guarantee ice will form. The additional variables for icing are infinite. Therefore, icing can be determined only if there is a physical presence of ice.”
NATA asked the FAA to rescind the draft letter of interpretation.