(5) Speed limitations (if any) and minimum temperature for deicing boot operation for airplanes equipped with boots.
(6) Environmental limitations for equipment operations as applicable (e.g., minimum temperature for boot operation or maximum altitude for boot operation).
(7) Minimum engine speed if the airframe ice protection system does not function properly below this speed.
(8) A list of required placards.
(9) For airplanes with unpowered roll controls and pneumatic deicing boots, a warning should be provided for severe icing that may result from environmental conditions outside the icing envelope established as the basis of the approval defined in Appendix C (reference the AFM information in paragraphs 12d(3) and (4)).
b. Operating Procedures Section .
(1) Section 25.1585(a)(6) requires that the pilot be provided with recommended procedures for the use of ice protection equipment. This should include any preflight action necessary to minimize the potential of enroute emergencies associated with the ice protection system. The system components should be described with sufficient clarity and depth that the pilot can understand their function. Unless flightcrew actions are accepted as normal airmanship, the appropriate procedures should be included in the FAA-approved AFM, AFM revision, or AFM supplement. These procedures should include proper pilot response to cockpit warnings, a means to diagnose system failures, and the use of the system(s) in a safe manner.
(2) Procedures should be provided to optimize airplane operation during penetration of icing conditions, including climb, holding, and approach configurations and speeds. The AFM should define when the ice protection equipment should be activated.
(3) Emergency or abnormal procedures, including procedures to be followed when ice protection systems fail and/or warning or monitor alerts occur, should be provided.
(4) For fluid anti-ice/deice systems, information and method(s) for determining the remaining flight operation time should be provided.
(5) For airplanes that cannot supply adequate electrical power for all systems at low engine speeds, load-shedding instructions should be provided to the pilot for approach and landing in icing conditions.
c. Performance Information Section . Data should be provided so that the maximum landing weight, as limited by approach and landing climb performance (§§ 25.121(d) and 25.119 respectively) can be determined in icing conditions. These data should include the effect of drag due to residual ice on protected and unprotected surfaces, the power extraction associated with ice protection system operation, and any changes in operating speeds due to icing. The effect on landing distance due to revised approach speeds, and/or landing configurations, should be shown.
d. Airworthiness Directives for Severe Icing Conditions .
(1) In October 1994, an accident involving a transport category airplane occurred in which severe icing conditions were reported in the area. During extensive testing the accident profile was replicated by ice shapes developed from testing in an icing cloud having droplets in the size range of freezing drizzle at a temperature near freezing. This condition created a ridge of ice aft of the deicing boots and forward of the ailerons, which resulted in uncommanded motion of the ailerons and rapid roll of the aircraft.
(2) Following this accident the FAA determined that flightcrews are not currently provided with the information necessary to determine when the airplane is operating in icing
21 conditions that have been shown to be unsafe and for which the airplane is not certificated; or what action to take when such conditions are encountered. Therefore, the FAA determined that flightcrews must be provided with such information, and must be made aware of certain visual cues that may indicate when the airplane is operating in atmospheric conditions that are outside the part 25, Appendix C icing envelope.
(3) The FAA is particularly concerned with airplanes that are equipped with pneumatic deicing boots and non-powered roll control systems, since non-powered roll flight controls do not have the physical advantage of hydraulic or electrical power to assist the pilot in overcoming the large control forces that may exist from differential pressure resulting from flow separation over the roll control surfaces. The FAA issued a series of Airworthiness Directives (AD’s) in April 1996 and February 1998 on airplanes equipped with pneumatic deicing boots and nonpowered roll control systems. The AD’s require revising the Airplane Flight Manual (AFM) to provide the flight crew with recognition cues for, and procedures for exiting from, severe icing conditions, and to limit or prohibit the use of various flight control devices. Other similarly equipped aircraft should also include this information in the AFM.
(4) The limitations and procedures specified in Airworthiness Directive (AD) 96-09-25 are an acceptable means of providing this information. These limitations and procedures include, but are not limited to, the following:
(a) Visual cues that the airplane is in severe icing conditions;
(b) Prohibition on the use of the autopilot when the visual cues are observed;
(c) All icing detection lights operative prior to flight into icing conditions at night;
(d) Immediate exiting of the severe icing conditions; and
(e) If the flaps are extended, do not retract them until the airframe is clear of ice.
Note: The retraction of the flaps is contingent upon the existence of a means to determine if the airframe is clear of ice.