f. The pilot should be familiar with any guidance provided in the AFM or POH. If the AFM does have a maximum flap limitation in icing, it is usually because of ICTS susceptibility.
A wing stall would be more common than an ICTS if the flap limitation was followed.
g. Increased power increases susceptibility to ICTS in some designs (depending on configuration), but not in others. Again, the pilot should consult the AFM or POH.
h. When ICTS or wing stall is a possibility, uncoordinated flight such as side or forward slips should be avoided and, to the extent possible, crosswind landings should be restricted because of their adverse effect on pitch control and the possibility of reduced directional control.
i. Landing with a tailwind component may result in more abrupt nose-down control inputs and should be avoided if possible. If an airplane has ice on the wings and tail, the pilot may be wise to exercise limited or no deployment of flaps, which will likely result in a higher than normal approach speed. Because of the higher speed approach, longer runways may be needed for this procedure.
7-10. ROLL UPSETS.
a. Roll upsets caused by ice accumulations forward of the ailerons also are possible during an icing encounter, particularly in SLD conditions. During the slow speeds associated with approach and landing, such control anomalies can become increasingly problematic. Pilots can remedy roll upsets using the following guidelines:
• Reduce the AOA by increasing airspeed or extending wing flaps to the first setting if at or below VFE (maximum flap extension speed.) If in a turn, the wings should be rolled level.
• Set the appropriate power, and monitor the airspeed and AOA.
• If the flaps are extended, do not retract them unless it can be determined that the upper surface of the airfoil is clear of ice. Retracting the flaps will increase the AOA at a given airspeed.
• Verify that the wing ice protection is functioning normally and symmetrically through visual observation of each wing. If there is a malfunction, follow the manufacturer’s instructions.
NOTE: These procedures are similar to those for wing stall recovery, and in some respects opposite from those for recovery from the ICTS.
b. Application of the incorrect procedure during an event can seriously compound the upset. Correct identification and application of the proper procedure is imperative. It is extremely important that the pilot maintain awareness of all possibilities during or following flight in icing.
Par 7-9 Page 53 (and 54)
Par 8-1 Page 55 CHAPTER 8. SUMMARY
a. Ice-contaminated aircraft have been involved in many accidents. Takeoff accidents have usually been due to failure to deice or anti-ice critical surfaces properly on the ground.
Proper deicing and anti-icing procedures are addressed in two other pilot guides, AC 120-58 and AC 135-17. This Pilot Guide focuses on ice that forms in flight, and should be useful to all pilots of fixed-wing aircraft. Any ice encountered in flight, even in trace amounts, can be dangerous. This guidance should help educate pilots about the potential hazards of in-flight icing, ways to avoid such hazards, and how to cope with potential hazards effectively.
b. The pilot of an aircraft that is not certificated for flight in icing conditions should avoid all icing conditions. This guide provides guidance on how to do this, and on how to exit icing conditions promptly and safely should they be inadvertently encountered.
c. The pilot of an aircraft that is certificated for flight in icing conditions can safely operate in the conditions for which the aircraft was evaluated during the certification process but should never become complacent about icing. Even short encounters with small amounts of rough icing can be very hazardous.
d. The pilot should be familiar with all information in the AFM or POH concerning flight in icing conditions and follow it carefully. Of particular importance are proper operation of ice protection systems and any airspeed minimums to be observed during or after flight in icing conditions. Airspeed loss can be very rapid, and without an autothrottle, the autopilot will not maintain airspeed. Monitor airspeed and do not rely on the airplane’s stall warning system in icing conditions. There are some icing conditions for which no aircraft is evaluated in the certification process, such as SLD conditions within or below clouds, and flight in these conditions can be very hazardous. The pilot should be familiar with any information in the AFM or POH relating to these conditions, including aircraft-specific cues for recognizing these hazardous condition.
Appendix 1 APPENDIX 1. AIRCRAFT ACCIDENTS RELATED TO ICING
1. American Eagle ATR-72 (Roselawn, Indiana).
a. Of the recent air carrier accidents, the one with arguably the most significant implications regarding in-flight icing is the October 31, 1994, crash of an ATR-72 turbopropeller transport aircraft. The aircraft was on a flight from Indianapolis, Indiana, to Chicago’s O’Hare International Airport, flying with the autopilot engaged and in a holding pattern, descending to 8,000 feet through supercooled clouds and SLD. Later analysis by the NTSB estimated that the supercooled drops in the area ranged between 0.1 mm and 2 mm in size.
b. Before the aircraft entered the hold, its engine RPM was increased to 86 percent as called for in the ATR-72’s AFM for flight in icing conditions (specified as true air temperature (TAT) of less than 7°C in the presence of visible moisture). As the aircraft began holding, the flaps were extended to 15 degrees to lower the aircraft’s AOA, and the engine RPM was reduced to 77 percent, presumably because the crew determined they were no longer flying in icing conditions. After holding for over half an hour, the aircraft was cleared to descend to 8,000 feet, and the crew retracted the flaps to avoid a flap overspeed warning.
c. According to the NTSB, the encounter with the icing conditions in the hold resulted in a ridge of ice accreting aft of the aircraft’s wing deicing boots and in front of the aircraft’s unpowered ailerons. As the aircraft descended to its cleared altitude, its AOA increased and the airflow began to separate in the area of the right aileron. This resulted in a sudden and unexpected aileron hinge reversal that exceeded the autopilot’s ability to control the aircraft, and it disconnected. This left the flightcrew in a full right-wing-down position within a quarter of a second, which was followed by a series of unsuccessful attempts to correct the aircraft’s attitude, resulting in a descent that at times reached 24,000 feet per minute and precipitated the structural failure of the aircraft’s elevators. The aircraft then impacted a soybean field at high speed resulting in the deaths of all 68 passengers and crew.
d. The NTSB’s investigation resulted in several findings, but ultimately, the most important regarding the effects of icing conditions on aircraft was the degree to which the conditions affected a properly certificated aircraft and the limited information available to the flightcrew with respect to the severity of the conditions they were experiencing.
2. Air Florida B-737 (Washington, District of Columbia).
a. Although this accident is well known because it illustrates the dangers of taking off without proper ground deicing, for the purposes of this AC, the accident offers another lesson with respect to icing and its hazards. On January 13, 1982, almost an hour after the B-737 had been deiced; it took off from Washington’s National Airport in light-to-moderate snowfall with temperatures below freezing. In addition to snow and ice forming on the aircraft fuselage during the extended taxi, ice had collected in the compressor inlet pressure probes of the two engines, apparently because the flightcrew neglected to turn on the engine anti-icing system. These inlets are used in conjunction with exhaust pressure to determine engine thrust settings for display in the cockpit as an Exhaust Pressure Ratio (EPR). As one of its functions, the engine’s anti-icing Page 1
Appendix 1 system is designed to maintain a flow of heated air over the compressor inlet to prevent the formation of ice on these probes.
b. As the flightcrew increased the engine throttles to takeoff thrust, the engines actually were developing less thrust than was indicated on the EPR gauges. This thrust deficit, combined with the accumulation of snow and ice on the wings, resulted in a stall immediately after rotation, with the aircraft climbing only to 200 or 300 feet before stalling and colliding with the 14th Street bridge.
c. While this accident, like almost all others, was caused by a combination of factors, it serves as an example to pilots that icing hazards affect not only aircraft aerodynamics but also aircraft instrumentation. In fact, studies conducted after the accident indicated that an immediate combined application of full power and lowered aircraft attitude theoretically could have allowed a safe recovery in a situation similar to this accident.
3. Northwest Orient B-727 (Thiells, New York).
a. Because this accident was a ferry flight and only the flightcrew of three was killed, it has not gained the notoriety of other airline crashes. However, it is significant to the subject matter of this AC, because it is an example of how a well-trained, professional flightcrew neglected to use the anti-icing equipment available on a modern aircraft and then became confused and disoriented by the inconsistent instrument indications that resulted.
b. On December 1, 1974, the aircraft in question was slated to conduct a nighttime ferry flight from New York’s John F. Kennedy International Airport to Buffalo, New York, to position for a return charter flight. After a normal takeoff, the aircraft was climbing to its assigned altitude of 31,000 feet when ATC received a series of radio transmissions from the flightcrew in which they declared an emergency and stated that they were out of control and in a stall. The aircraft descended rapidly, broke up in flight, and crashed in a forest near Bear Mountain, New York.
c. NTSB investigators examining the aircraft wreckage the next morning discovered that the two pitot head heater switches were in the “off” position. An analysis of the aircraft flight data recorder and cockpit voice recorder (CVR) revealed that the before-takeoff checklist was followed incorrectly by the first officer, resulting in the pitot heat being turned off instead of on as required by the checklist.
d. Investigators determined that as the aircraft was climbing through 16,000 feet at 305 knots and at a climb rate of 2,500 feet per minute, airspeed and vertical speed indicators began to climb, without any change to the engine power settings, to a point that actually exceeded the aircraft’s capability. This created confusion among the flightcrew, but the CVR revealed that they attributed the aircraft’s performance to the aircraft’s light load. As the aircraft reached 23,000 feet, the mach overspeed warning came on and the crew continued to pull on their yokes to trade speed for altitude. This resulted in an excessive AOA followed by a stall.
The flightcrew became disoriented and confused by the series of alarms and contradictory indications, resulting in a spiral dive from which they could not recover. The encounter with icing conditions was further worsened because the B-727 has tail-mounted pitot tubes for the Page 2
Appendix 1 elevator feel system that also were blocked with ice. The feel system modulates the amount of force the pilots have to exert on the elevator controls with changes in speed. Because the pitot tubes were covered with ice, smaller movements of the controls resulted in higher control movements and eventually higher vertical acceleration forces on the aircraft.
e. While the loss of a pitot static system is something that all instrument-rated pilots are trained to cope with, the insidious nature of such system malfunctions can result in confusion because the instruments often provide erroneous readings without necessarily indicating a system failure. Pilots must remain vigilant for such unusual indications from their instruments and instead rely on attitude flying.
4. Mitsubishi MU-2B-36 (Malad City, Idaho).
a. This accident demonstrates the importance of ensuring that ice protection systems are operational when flying into an environment where the possibility of encountering icing conditions exists. It also highlights how critical airspeed awareness is, especially while flying in icing conditions.
b. On January 15, 1996, a Mitsubishi MU-2 departed Salt Lake City, Utah, and climbed to 16,000 feet on a part 91 IFR flight to Pocatello, Idaho. The airplane encountered structural icing conditions while in cruise, and according to radar data, began slowing from a cruise speed of about 190 knots while slightly deviating from heading and altitude. The airspeed decreased to about 100 knots and the flightcrew declared an unspecified emergency; then radio contact was lost. The airplane began a right turn, then entered a steep descent and crashed. All aboard the airplane were killed because of the impact. The pilot of a Beech 1900 about 12 minutes in trail of the MU-2 stated that he encountered moderate rime ice at 16,000 feet. The Beech pilot activated the pneumatic boots three times and descended to 12,000 feet to exit the icing conditions. The MU-2 AFM warned that during flight in icing conditions, stall warning devices may not be accurate and should not be relied on, and, to minimize ice accumulation, pilots should maintain a minimum cruise speed of 180 knots or exit the icing conditions. An investigation determined that the captain of the MU-2 was aware of deficiencies in the timer for the pneumatic boots, along with other maintenance deficiencies. Although icing conditions were forecast in the destination area, no icing was forecast for the en route portion of the flight.
c. The NTSB determined that the probable cause of the accident was continued flight by the flightcrew into icing conditions with known faulty pneumatic equipment, structural (airframe) ice, and failure of the flightcrew to maintain adequate airspeed, which resulted in the loss of aircraft control and collision with terrain. The en route icing condition, which was not forecast, was also cited as a factor relating to the accident.
5. Piper PA-34-200T (Des Moines, Iowa).
a. The circumstances surrounding this accident demonstrate the dangers associated with tailplane icing and why proper use of deicing equipment is critical to flying in icing conditions.
b. On January 9, 1996, a Piper PA-34 departed Sioux Center, IA, bound for Des Moines, IA (DSM). In his written statement, the pilot stated that he flew a normal ILS approach with 10 degrees of flaps extended. Upon breaking out of the clouds, he checked for ice with a Page 3
Appendix 1 flashlight, and observed the windshield and the left inboard wing, to be free of ice. He elected to fly the approach fast, and with 25 degrees of flaps.
c. Upon crossing the runway threshold at DSM, the pilot stated that he lowered the flaps to 25 degrees, and that the airplane responded by pitching down. The pilot then stated that he immediately released the flaps and added power, but said the airplane was “basically uncontrollable at this point.” He then reduced power and lowered the flaps before striking the runway on its centerline and sliding 1,000 feet before coming to a stop. The accident resulted in serious injury to the pilot, who was the sole occupant.
d. Examination of the wreckage revealed heavy impact damage to the airplane’s forward fuselage, engines, and wings. Approximately one-half inch of rime ice was observed adhering to the leading edges of the left and right horizontal stabilizers and along the leading edge of the vertical stabilizer.
e. The DSM airport’s ATIS, at 2256 EST, reported that a pilot in a Cessna 210 experienced light to mixed icing, 8 miles northeast of the airport, between 2,500 and 3,700 feet MSL.
f. The NTSB determined the probable cause of the accident was the pilot’s failure to use the airplane’s deicing system, which resulted in an accumulation of empennage (tail assembly of an airplane) ice and a tailplane stall. Factors relating to this accident were the icing conditions and the pilot’s intentional flight into those known conditions.
6. Embraer EMB-120 (West Palm Beach, Florida).
a. This accident is another example of a stall in icing conditions, suspected to be SLD.
The NTSB was unable to determine if the stall warning system activated prior to stall. This accident also illustrates the rapid loss of airspeed that can occur in icing conditions and the need for pilots to monitor airspeed closely in icing conditions, even with autopilot engaged.
b. On March 19, 2001, Embraer EMB-120, operated by Comair Airlines, Inc., was en route from Nassau International Airport, Bahamas, to Orlando International Airport, Florida.
While in cruise flight at 17,000 feet, the aircraft encountered icing conditions, and departed controlled flight, descending to an altitude of about 10,000 feet. The pilots recovered control of the airplane and diverted to West Palm Beach, Florida, where they landed without further incident. Though none of the 28 persons on board was injured, the airplane sustained substantial damage to the elevators and the horizontal stabilizer.
c. In post accident interviews, the captain stated that while in visual conditions, the airplane flew normally. Flight data recorder (FDR) data indicate that about 7 minutes before the upset occurred, the airplane was at about 17,000 feet, with the autopilot engaged and airspeed stabilized near 200 knots. The data indicates the airspeed slowed to 185 knots over a several minute period as the autopilot began trimming airplane nose-up (ANU) to maintain altitude. The airspeed then decreased to about 137 knots over the next 3 minutes. The airplane continued to maintain a constant altitude as the autopilot trimmed the airplane from about 0 to about 7 degrees ANU. The first officer stated that immediately before the upset occurred, he switched the leading-edge deicing system inflation cycles switch from “light” to “heavy” and the propeller Page 4
Appendix 1 deicing system cycles switch from “norm” to “cold” because he saw “more ice accumulation than he had ever seen” on the wing and spinner. FDR data indicate that when torque indications for both engines were about 55 percent and the airspeed was about 141 knots, the autopilot was disengaged. The airplane then pitched down and rolled about 80 degrees to the left, then rolled back to near level. During the next 20 seconds, engine torque increased to about 98 percent on both engines, the airplane rolled about 110 degrees to the left, returned to level flight, rolled about 130 degrees to the right, returned to level flight, then rolled 360 degrees to the right before returning to near wings level, with torque on both engines stabilized at about 22 percent. The airplane’s behavior during the upset is consistent with an ice-induced stall event.
d. The first officer stated in post accident interviews that the stick shaker and aural stall warning, which is part of the airplane’s stall warning/protection system, activated but did not indicate whether it was before, during, or after the upset. The Safety Board’s investigation could not precisely determine whether or when the stick shaker and aural stall warning activated.
e. Meteorological data at the time of the accident indicated that Comair flight may have encountered an area of icing conducive to the formation of super-cooled large droplets (SLD).
The EMB-120 is not certified for flight in SLD conditions. FDR data indicate that airspeed had decreased to only about 137 knots before control of the airplane became difficult and altitude was no longer maintained. However, according to the Embraer EMB-120 AFM performance section, the airplane stalling speed is about 115 knots calibrated airspeed for an airplane at the accident airplane’s approximate gross weight at the time of the event (23,800 pounds).
f. The National Transportation Safety Board determined the probable cause(s) of this accident as follows:
• The failure of the flightcrew to maintain airspeed during an encounter with severe icing conditions.
• This resulted in an inadvertent stall, loss of control, and structural damage to the airplane.
7. Raytheon (Beech) BE-90 (Rawlins, Wyoming).
a. This accident is another example of a stall in icing conditions. The need for extra vigilance by pilots near a destination airport reporting precipitation (snow) near freezing is highlighted in this accident. The ice accretions on the airplane suggest the conditions may have been worse than forecast and exceeded part 25, appendix C criteria.
b. On January 11, 2005, a BE-90, operating as an air ambulance was flying from Steamboat Springs, Colorado (SBS), to Rawlins Municipal Airport/Harvey Field (RWL).
Approaching RWL, the pilot initiated a right turn outbound to maneuver for the final approach course of the VOR/GPS approach to runway 22. On the inbound course to the airport, the airplane impacted mountainous terrain, approximately 2.5 nautical miles east-northeast of the airport. The airplane, configured for landing, struck the terrain wings level, in a 45-degree nose-down dive, consistent with impact following an aerodynamic stall. There were three fatalities and one serious injury.
Appendix 1
c. Approximately 5 minutes before the accident, the ASOS at RWL reported the weather as few clouds at 500 feet above ground level (AGL), scattered clouds at 900 feet AGL, overcast ceiling at 1,500 feet AGL, visibility 2 miles with light snow and mist, temperature 32°F, dew point 32°F, winds 250 degrees at 3 knots, and altimeter 29.35 inches of mercury (Hg).
Before departing SBS, the pilot received a weather briefing from Denver Flight Service. The briefer told the pilot that there was a band of light to moderate snow shower activity half way between Rock Springs and Rawlins, spreading to the northeast. The briefer told the pilot there were adverse conditions and flight precautions along his route for occasional mountain or terrain obscurations. The pilot responded that he planned to fly instrument flight rules for the entire flight.
d. The Surface Analysis showed a north-south stationary front positioned along the front range of the Rocky Mountains beginning at the Wyoming/Montana border and extending south into north-central Colorado. Station plots indicated patchy snow over western Colorado and Wyoming. The most recent AIRMET reported, “Occasional moderate rime, or mixed icing in clouds and precipitation between the freezing level and flight level 220.” The freezing level for the area encompassing the route of flight began at the surface. Witnesses in the vicinity of RWL reported surface weather conditions varying from freezing rain to heavy snow. The Current Icing Product (CIP) showed no potential for SLD, yet an examination of the airplane showed clear ice up to 1½ inches thick adhering to the vertical stabilizer, the left and right wings, the right main landing gear tire, and the right propeller.
e. The airplane’s aerodynamic performance was degraded due to the ice contamination, leading to a stall. An examination of the airplane’s systems revealed no anomalies. FAA Advisory Circular (AC) 135-15, Emergency Medical Services/Airplane (EMS/A), addresses several subject areas that were not practiced by the operator, including the recommendation of avoiding flight in icing weather whenever possible.
f. The National Transportation Safety Board determined that the probable cause of this accident was the pilot’s inadvertent flight into adverse weather (severe icing) conditions, resulting in an aerodynamic stall and impact with rising, mountainous terrain during approach. A factor contributing to the accident was the pilot’s inadequate planning for the forecasted icing conditions.
8. Cirrus SR-22 (Childersburg, Alabama).
a. This accident shows the importance of obtaining an up-to-date weather briefing that includes icing forecasts and freezing levels. It also highlights the performance degradation that can occur when an airplane not certificated for flight in icing exceeds its limits.
b. On January 13, 2006, a Cirrus SR-22 was en route from Birmingham, AL to Orlando, FL, when it encountered icing conditions and entered an inadvertent stall and spin. The pilot deployed the ballistic recovery system parachute, and the aircraft descended into the trees leaving the three occupants of the aircraft uninjured.
c. The night before the accident, the pilot obtained a full Direct User Access Terminal (DUATS) briefing, though the briefing was not valid for the time of the accident. The National Page 6
Appendix 1 Weather Service (NWS) issued an AIRMET Zulu update 3 for icing and freezing level data valid from 1445 CST until 2100 CST. The advisory warned of occasional moderate to mixed icing-in-clouds and in precipitation between 3,000 to 8,000 feet. Within the boundaries of the advisory were the departure airport and the accident site. The pilot requested an abbreviated DUATS weather briefing at 1244 EST for his route of flight. The in-flight advisories were to expire at 1500 CST. The briefing provided several adverse weather phenomena impacting the route of flight from icing, turbulence, and thunderstorms. The pilot stated he was not aware of AIRMET ZULU UPT 3 that was issued by the NWS before he departed Birmingham, though the airplane was equipped with an XM Satellite radio and the AIRMET was transmitted by the NWS over the XM radio installed in the airplane. This was significant, considering the airplane is not certificated for flight into icing conditions.
d. The pilot stated the flight departed from runway 24 and he contacted the air traffic controller on the radio. ATC radar identified the aircraft and the pilot was instructed to climb to 7,000 feet and proceed direct to HANDE intersection. With the autopilot engaged, the airplane entered the clouds at 5,000 feet, climbing at 120 knots. Upon reaching 7,000 feet, the airplane encountered icing conditions. The pilot informed the controller that he would like to climb to 9,000 feet and that was approved.
e. As the airplane reached the cloud tops in visual flight conditions at 8,000 feet, the airplane began to buffet. The pilot looked at his airspeed indicator and it indicated 80 knots. A stall ensued, followed by a spin that descended the airplane back into instrument flight conditions. The pilot deployed the ballistic parachute system and informed the air traffic controller of his actions. The airplane descended under the parachute canopy into the trees.
f. The NTSB determined the probable cause(s) of this accident as follows:
(1) The pilot’s inadequate preflight planning, failure to obtain a current weather briefing, and his decision to operate the airplane into a known area of icing outside the airplanes certification standards.
(2) This resulted in the aircraft accumulating ice, a loss of airspeed, an inadvertent stall/spin, and subsequent collision with trees.
Appendix 2 APPENDIX 2. REGULATORY ISSUES RELATED TO ICING Title 14 CFR parts 91, 121, 125, and 135 specify the responsibilities of flightcrews concerning flight in icing conditions. Pilots are advised to check the current regulations for revisions. They are noted here for reference only and to illustrate the degree of similarity between parts 91, 121, 125, and 135 with respect to regulation of flight into icing conditions. An important distinction in each of these regulations is the restriction on flight into “known or forecast” conditions. Because of the limitations of icing forecasts, it is admittedly difficult for pilots to be certain whether the conditions in which they are flying actually will result in an icing encounter, and it is even more difficult to determine the severity of the possible encounter. Pilots can be caught inadvertently in icing conditions that exceed these legal limits.
General operating and flight rules for GA aircraft are found in part 91, but not all rules within part 91 are applicable to all GA aircraft. Section 91.501 states that the rules in subpart F apply only to large and turbojet-powered multiengine airplanes that are not covered by parts 121, 125, 129, 135, and 137. Section 91.527, Operating in icing conditions, falls within subpart F and thus is not applicable to all GA aircraft.
1. Part 91 Icing Regulations.
a. IFR. No pilot may fly an airplane under IFR into known or forecast moderate icing conditions unless one or more of the following apply:
(1) The aircraft has ice protection provisions that meet the requirements in 14 CFR part 135, appendix A, paragraph 34 of Special Federal Aviation Regulation (SFAR) No. 23.
(2) The aircraft has ice protection provisions that meet the requirements for transport category airplane type certification.
(3) The aircraft has functioning deicing or anti-icing equipment protecting each propeller, windshield, wing, stabilizing surface, control surface, airspeed instrument, altimeter, rate of climb instrument, and flight attitude instrument system.
b. VFR. No pilot may fly an airplane under VFR into known light or moderate icing conditions unless one or more of the following apply:
(1) The aircraft has ice protection provisions that meet the requirements in SFAR 23 paragraph 34 (same as part 135, appendix A, paragraph 34, and § 23.1419 at Amendment 23-14).
(2) The aircraft has ice protection provisions that meet the requirements for transport category airplane type certification.
(3) The aircraft has functioning deicing or anti-icing equipment protecting each propeller, windshield, wing, stabilizing surface vertical tail, control surface flap, aileron, elevator, airspeed instrument, altimeter, rate of climb instrument, and flight attitude instrument system.
Appendix 2
c. Severe Icing. No pilot may fly an airplane into known or forecast severe icing conditions unless:
(1) The airplane has ice protection provisions that meet the requirements in SFAR 23 paragraph 34, or;
(2) The airplane has ice protection provisions that meet the requirements for transport category airplane type certification.
NOTE: Even airplanes approved for flight into known icing conditions should not fly into severe icing. Many Airplane Flight Manual Limitations Sections require an immediate exit when these types of conditions are encountered.
NOTE: Airplane certification for flight into known icing conditions does not include freezing drizzle and freezing rain. In fact, some airplanes are prohibited from flying into freezing drizzle or freezing rain, regardless of its intensity. These conditions are very dangerous and can cause ice to form behind the protected areas. (See § 91.527, Operating in icing conditions, for the exact language of the above regulations.)
d. Aircraft Not Certificated for Flight in Icing Conditions.
(1) Aircraft certificated since the mid-1970s that are not certificated for flight in icing conditions will have a limitation in the AFM or POH and possibly a placard on the aircraft stating that flight into “known icing conditions” is prohibited. “Known icing conditions,” as defined in the AIM, are conditions in which ice is observed or detected in flight, by your aircraft or another aircraft, or an airport. Such limitations are binding under § 91.9, Civil aircraft flight manual, marking, and placard requirements, and this regulation takes precedence over §§ 91.527 and 135.227. However, if a pilot of such an airplane were to takeoff and fly in area in which icing is forecast (e.g., AIRMET Zulu), it is expected the pilot will through preflight planning and in-flight execution:
(a) First attempt to avoid areas of “potential icing conditions”, which are areas of visible moisture such as clouds at temperatures below freezing;
(b) If that is not practical, attempt to avoid areas of forecast icing by all tools available (e.g., AIRMETs, SIGMETs, CIP and FIP); and
(c) If icing is encountered, declare an emergency and exit the conditions immediately.
NOTE: Failure to follow the section above may result in enforcement action under § 91.103, Preflight action, or § 91.13, Careless or reckless operation, depending on the circumstances and the actions a reasonable pilot will take.
Pilot should remember, these airplanes were not tested for inadvertent encounters and since most icing conditions consist of small drops and low Page 2
Appendix 2 LWC, should not assume their airplane can tolerate all icing conditions after one successful encounter.
(2) Aircraft certificated prior to the mid-1970s that are not certificated for flight in icing conditions may not have any prohibitions stated in the AFM or POH. If not, they are not covered by either § 91.527 or § 91.9. However, given that information on the dangers of aircraft icing has been widely disseminated for many years, certain actions, such as taking off with wings coated with ice, could be interpreted as prohibited under § 91.13.
2. Part 121 Icing Regulations (see § 121.341, Equipment for Operations in Icing Conditions).
a. Icing Conditions. No person may fly an airplane in icing conditions unless one or more of the following apply:
(1) The aircraft has functioning deicing or anti-icing equipment protecting each propeller, windshield, wing, stabilizing surface, control surface, airspeed instrument, altimeter, rate of climb instrument, and flight attitude instrument system.
(2) The aircraft is type certificated under the transport category airworthiness requirements relating to ice protection.
(3) The aircraft is a non-transport category airplane type certificated after December 31, 1964, which meets the provisions detailed below.
b. Non-Transport Category Airplanes Type Certificated After December 31, 1964.
(1) IFR. No pilot may fly a non-transport category airplane under IFR type cerftificated after December 31, 1964, into known or forecast light or moderate icing conditions unless one or more of the following apply:
(a) The aircraft has ice protection provisions that meet part 135, appendix A, paragraph 34.
(b) The aircraft has ice protection provisions that meet the requirements for transport category airplane type certification.
(c) The aircraft has functioning deicing or anti-icing equipment protecting each propeller, windshield, wing, stabilizing surface, control surface, airspeed instrument, altimeter, rate of climb instrument, and flight attitude instrument system.
(2) VFR. No pilot may fly a non-transport category airplane under VFR type certificated after December 31, 1964, into known light or moderate icing conditions unless one or more of the following apply:
(a) The aircraft has ice protection provisions that meet part 135, appendix A, paragraph 34.