Most Wanted
Transportation Safety
Improvements
AVIATION
Reduce Dangers to Aircraft Flying in Icing Conditions
Objectives
Importance
The 1994 in-flight icing encounter and subsequent loss of control and crash of a commuter airliner in Roselawn, Indiana, which took 68 lives, prompted the Safety Board to examine the issue of airframe structural icing and conclude that the icing certification process has been inadequate because the process has not required manufacturers to demonstrate the airplane’s flight handling and stall characteristics under a realistic range of adverse ice accretion/flight-handling conditions. The FAA has not adopted a systematic and proactive approach to the certification and operational issues of turbine-engine-driven transport-category airplane icing.
The consequences of operating an airplane in icing conditions without first having thoroughly demonstrated adequate handling/controllability characteristics in those conditions are sufficiently severe that they warrant a thorough certification test program, including the application of revised standards to airplanes currently certificated for flight in icing conditions.
Revise Icing Certification Criteria and Testing
As a result of the Roselawn, Indiana, accident, the Safety Board called on the FAA to revise the icing criteria and icing testing requirements necessary for an airplane design to be approved within the United States, and the operational requirements that specify under what icing conditions it is permissible to operate an aircraft. More than 10 years ago, this work was referred to an ARAC, which has recommended to the FAA changes to the design requirements for new airplanes to evaluate performance and handling characteristics in icing conditions. In March 2002, 6 years after it started this work, the ARAC approved a concept to revise the icing criteria in the design requirements for new airplanes.
Currently, there are five rulemaking activities concerning icing:
In response to the second rulemaking activity, on April 26, 2007, the FAA published an NPRM, “Activation of Ice Protection; Proposed Rule,” which proposes to amend Part 25 to require a means to ensure timely activation of the airframe ice protection system (IPS) on newly certified transport category airplanes for flight in icing conditions. Specifically, the rule would require that airplane manufacturers provide a means to detect ice and to ensure that the airframe IPS is activated.
Within the past year, the FAA has been taking action in response to these recommendations. In addition to the April 26, 2007, NPRM concerning IPS activation, on August 8, 2007, the FAA published the final rule concerning revisions to Part 25 for evaluating airplane performance and handling characteristics in icing conditions. The final rule became effective on October 9, 2007. The ARAC is still working on regulations concerning SLD and mixed-phase icing for both Part 25 and Part 23. The Safety Board has learned of FAA activities in response to recommendations concerning icing issued as a result of the February 16, 2005, crash of a Cessna Citation 560 during approach to landing in icing conditions at Pueblo, Colorado. This accident occurred in SLD conditions, and FAA and Cessna flight testing in response to the investigation used procedures and tests suggested by the ARAC to analyze airplane handling characteristics in SLD conditions. This suggests that the FAA may be near developing and issuing regulations concerning SLD. However, the FAA has not provided any projected dates for development and issuance of an NPRM and final rule. The pace of the FAA’s activities in response to these recommendations remains unacceptably slow, despite recent encouraging action.
As a result of the Safety Board’s investigation of the in-flight encounter with icing and subsequent uncontrolled collision with terrain of Comair flight 3272, an Embraer 120RT, near Monroe, Michigan, on January 9, 1997, in which all 29 persons onboard the airplane were killed, the Safety Board asked the FAA to review the icing certification of all turbopropeller-driven airplanes currently certificated for operation in icing conditions, and to perform additional testing. On August 16, 2006, the FAA issued AC 20-73A, “Aircraft Ice Protection” which includes certification guidance relative to the effects and criticality of deicing boot intercycle and residual ice accumulations, and ice accumulations on unprotected surfaces aft of protected surfaces. The FAA and NASA conducted testing and research on these issues in 1999 and 2000. The FAA stated in a letter to the Safety Board in September 2001 that additional testing and research were necessary to develop the needed guidance, and that it was developing and pursuing this research. In an October 26, 2005, letter, the FAA indicated that the revisions to the AC were based on the testing and research performed in 1999 and 2000. As part of its evaluation of the revised AC, the Safety Board has asked the FAA whether additional research and testing were conducted after the FAA’s September 2001 letter.
The icing certification regulations and advisory material developed by the FAA are sufficiently developed to determine whether additional action is required for any airplanes currently certificated and in service. The FAA has stated that no unsafe conditions exist that warrant actions beyond those that have already been completed or are in the process of being completed. The Board is concerned that the FAA has reached this conclusion based on a lack of accidents or serious incidents. During the 1990s, a number of accidents occurred involving airplanes that had passed the certification standards and for which the FAA believed there was no unsafe condition requiring action. Before another accident or serious incident occurs, the FAA should evaluate all existing turbo-propeller driven airplanes in service using the new information available, such as critical ice shapes and stall warning margins in icing conditions.
Action Remaining
Complete efforts to revise icing certification criteria, testing requirements, and restrictions on operations in icing conditions. Evaluate all aircraft certified for flight in icing conditions using the new criteria and standards.
Safety Recommendations
A-96-54 (FAA)
Issued August 15, 1996
Added to the Most Wanted List: 1997
Status: Open—Unacceptable Response
Revise the icing criteria published in 14 [Code of Federal Regulations] CFR Parts 23 and 25, in light of both recent research into aircraft ice accretion under varying conditions of liquid water content, drop size distribution, and temperature, and recent developments in both the design and use of aircraft. Also, expand the Appendix C icing certification envelope to include freezing drizzle/freezing rain and mixed water/ice crystal conditions, as necessary. (Source:Report on the in-flight icing encounter and loss of control of American Eagle flight 4184, ATR 72-212, near Roselawn, Indiana, on October 31, 1994 [NTSB/AAR-96-01])
A-96-56 (FAA)
Issued August 15, 1996
Added to the Most Wanted List: 1997
Status: Open—Unacceptable Response
Revise the icing certification testing regulation to ensure that airplanes are properly tested for all conditions in which they are authorized to operate, or are otherwise shown to be capable of safe flight into such conditions. If safe operations cannot be demonstrated by the manufacturer, operational limitations should be imposed to prohibit flight in such conditions and flightcrews should be provided with the means to positively determine when they are in icing conditions that exceed the limits for aircraft certification. (Source:Report on the in-flight icing encounter and loss of control of American Eagle flight 4184, ATR 72-212, near Roselawn, Indiana, on October 31, 1994 [NTSB/AAR-96-01])
A-98-92 (FAA)
Issued November 30, 1998
Added to the Most Wanted List: 2003
Status: Open—Unacceptable Response
With the National Aeronautics and Space Administration [NASA] and other interested aviation organizations, conduct additional research to identify realistic ice accumulations, to include intercycle and residual ice accumulations and ice accumulations on unprotected surfaces aft of the deicing boots, and to determine the effects and criticality of such ice accumulations; further, the information developed through such research should be incorporated into aircraft certification requirements and pilot training programs at all levels. (Source:Report on the in-flight icing encounter and uncontrolled collision with terrain of Comair flight 3272, an Embraer EMB-120RT, near Monroe, Michigan, on January 9, 1997 [NTSB/AAR-98-04])
A-07-16 (FAA)
Issued February 27, 2007 (Superseded A-98-100)
Added to the Most Wanted List: 2007
Status: Open—Unacceptable Response
When the revised icing certification standards and criteria are complete, review the icing certification of pneumatic deice boot-equipped airplanes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the requirements of the revised icing certification standards. (Source: Report on crash during approach to landing, Circuit City Stores, Inc., Cessna Citation 560, N500AT, Pueblo, Colorado, on February 16, 2005. [NTSB/AAR-07-02])
November 2007