Honorable Deborah Hersman, NTSB Board MemberTestimony of Deborah A.P. Hersman, Chairman
National Transportation Safety Board
Before the Aviation Subcommittee, Committee on Transportation and Infrastructure
U.S. House of Representatives
Aircraft Icing
February 24, 2010

 

 


Chairman Costello, Mr. Petri, and Members of the Subcommittee:

Thank you for the opportunity to join the discussion today regarding the safety of aircraft in icing conditions.  This is an issue of great concern to the National Transportation Safety Board (NTSB), and we appreciate the opportunity to offer our viewpoint.

The NTSB is an independent Federal agency chartered by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation.  Last week, the NTSB adopted its Most Wanted List of Transportation Safety Improvements for 2010, which includes a number of open recommendations, including four which seek to reduce the dangers to aircraft flying in icing conditions.  The Board voted to retain the issue area “Reduce Dangers to Aircraft Flying in Icing Conditions” on the Most Wanted List and also to retain the red classification which reflects an unacceptable response to this issue area which has been on the Most Wanted List since 1997. 

Since its inception in 1990, the Most Wanted List represents a group of safety recommendations selected for intensive follow-up.  The recommendations are combined into issue areas, such as in-flight structural aircraft icing.  These recommendations are selected because they will benefit or enhance the safety of the national transportation system; have a high level of public visibility or interest; or will benefit from this special form of encouragement and heightened attention. 

From 1998 to 2007, the NTSB has investigated fifty Part 121 and 135, and 214 General Aviation accidents involving airplane icing, resulting in 202 fatalities. The accidents have involved aircraft, powerplants, aircraft systems (excluding carbureter icing) and/or runway and surface conditions.  During that same period of time, the NTSB has issued 48 recommendations addressing various safety issues that, if addressed, would improve aviation safety.  While the NTSB relies on others to implement our recommendations, we have worked to educate the pilot community about some of the hazards associated with icing conditions through Safety Alerts (Ground Aircraft Icing – December 2006; De-ice Boot Activation – December 2008).

The following tables represent the range of investigations and recommendations that the NTSB has addressed between 1998 and 2007.  However, my testimony today will focus on the areas addressed in our Most Wanted List.

NTSB Accident Records 1998-2007
Involving U.S.-Registered Airplanes
Aircraft/Powerplant/Systems Icing (other than carburetor icing)
  Total Accidents Fatal Accidents Fatalities
Part 121 1 0 0
Part 135 36 15 27
Part 91, 137, and 125 163 79 175
Total 200 94 202

NTSB Accident Records 1998-2007
Involving U.S.-Registered Airplanes
Runway/Surface Icing
  Total Accidents Fatal Accidents Fatalities
Part 121 4 0 0
Part 135 10 0 0
Part 91, 137, and 125 54 0 0
Total 68 0 0

One Part 135 accident (CHI00LA073) and three part 91 accidents (FTW00LA084, CHI01LA086, and CHI03LA038) cited both airframe/powerplant/systems and runway/surface icing and appear in both tables.

Safety Recommendations Issued 1998-2007 Involving Icing
Topic Total
Engine Icing 1
In-flight  Icing 32
Runway and Ground 9
Total 48*

* 2 of the 48 recommendations were “Closed –Reconsidered” and therefore not included in the status count.

Safety Recommendations Issued 1998-2007 Involving Icing
Status of Recommendations Total Percentage of Recommendations
Open – Acceptable 16 35%
Open - Unacceptable 4 9%
Open – Awaiting Response 1 2%
Closed – Acceptable 19 41%
Closed - Unacceptable 6 13%
Total 46  

The NTSB has long been concerned about aircraft operating in icing conditions.  In September 1981, the NTSB published a report entitled “Aircraft Icing Avoidance and Protection,” which recommended that the FAA review the icing certification criteria. The report was the result of a special study following a series of icing-related accidents in which the NTSB identified concerns about aircraft operations in icing conditions and the varying consequences that ice accretions had on different aircraft types. As a result of two accidents during the 1990s, the NTSB became concerned about airplanes that fly in supercooled large droplet (SLD) conditions, and that use pneumatic boots to deice the aircraft in flight. These aircraft are typically, but not exclusively, turbo-prop aircraft that use pneumatic boots and fly at altitudes where they are more likely to encounter SLD conditions.

A significant icing accident occurred in 1994 in Roselawn, Indiana, involving an American Eagle ATR-72 in-flight icing encounter and subsequent loss of control, resulting in a crash that claimed 68 lives.  That accident investigation prompted the NTSB to re-examine the issue of airframe structural icing and conclude that the icing certification process continued to be inadequate because it did not require manufacturers to demonstrate the airplane’s flight handling and stall characteristic under a realistic range of adverse ice accretion conditions, including supercooled large droplets. 

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 application of revised standards to airplanes currently certificated for flight in icing conditions.

On January 9, 1997, a Comair Embraer EMB-120 departed controlled flight and crashed in icing conditions over Monroe, Michigan, while on approach to Detroit Metropolitan Airport.  All 29 people on board were killed.  The investigation of this accident, and of several control upset incidents that occurred prior to the Monroe accident that involved a delayed activation of the deice boots, revealed a widespread and firmly held, but incorrect, belief within the aviation community that the activation of deice boots should be delayed until ¼ to ½ inch of ice builds up to prevent “ice bridging.”  As a result, in many cases, flight crews do not activate the deice boots until after the build up of dangerous accumulations of ice on the aircraft.

In both the Roselawn and Monroe accidents, the pilots were using the autopilot before the icing-induced upset began.  Because the pilots were not manually flying the aircraft, they were not aware that the autopilot was having increasing difficulty maintaining stable flight until the autopilot suddenly disconnected, and the airplane entered an uncontrollable flight regime.

NTSB recommendations stemming from the Roselawn and the Monroe accidents called on the FAA to use current research on freezing rain and SLD to revise the way aircraft are designed and approved for flight in icing conditions; to apply revised icing requirements to currently certificated aircraft; and to require the pilots of airplanes with pneumatic deice boots to activate the boots as soon as the airplane enters icing conditions.  The FAA referred this work to an Aviation Rulemaking Advisory Committee (ARAC) more than 10 years ago.  Six years later, the ARAC approved a concept to revise the icing design requirements for new airplanes.  In December 2005, the ARAC completed its final report and recommended appropriate revisions to the design and operational requirements for flight in icing conditions.  In the more than four years since that report, the FAA has yet to issue a notice of proposed rulemaking (NPRM) to require consideration of more realistic icing conditions.

In the last few years the FAA has issued a number of final and proposed rules; some of those actions have been responsive to NTSB recommendations. On August 3, 2007, the FAA issued a final rule that revised the certification standards for the handling and controllability characteristics of newly designed Part 25 aircraft in icing conditions; however the rule did not include revisions to reflect SLD conditions, a particularly dangerous flight environment that the NTSB asked the FAA to address.  On August 3, 2009, the FAA issued a final rule regarding the activation of ice protection systems on newly designed Part 25 aircraft certified for flight in icing conditions.  On November 23, 2009, the FAA issued an NPRM regarding activation of the ice protection system on aircraft operated under Part 121.  The NTSB has commented on the NPRM which does not address other categories of aircraft such as business aircraft and Part 135 air-taxi operations or those aircraft weighing over 60,000 pounds, effectively exempting some aircraft types operating in regional airline operations such as the Bombardier DHC-8, Q-400.  In addition, the NTSB recommendation that prompted this NPRM resulted from the Pueblo, Colorado crash of a business jet operating under Part 91.  Therefore, the NPRM would not have prevented that accident.

While the FAA’s rules have addressed some of the recommendations relating to deice boot operations, not all of the NTSB recommendations have been fully addressed.  In particular, the NTSB has recommended that the FAA use a full range of icing conditions, including SLD, for icing certification testing.  This would include freezing rain, freezing drizzle, and freezing mist.

Unfortunately, the NTSB continues to investigate accidents and incidents in which in-flight icing has been a factor.  Each of the following incidents or accidents reinforces the need for the FAA to address SLD in icing certification:

Finally, the NTSB is investigating an accident that occurred in January 2009, in Lubbock, Texas, involving an ATR‑42 that was on a final approach to the airport.  During the NTSB’s two-day public hearing in September 2009, factual information established that this accident involved a flap asymmetry and the autopilot disconnected when the stick shaker activated.  The captain declined to perform a go-around, even when it was suggested by the first officer.  The captain took control of the aircraft and it subsequently crashed 300 feet short of the runway and was destroyed in post-crash fire.  Airframe icing was noted by the flightcrew.  The National Weather Service had forecast light freezing drizzle, which by definition is an SLD condition.  However, because severe icing conditions were not forecast or reported, the air carrier operating specification, approved by the FAA, allowed the flight to be dispatched into such conditions.  Testimony at the public hearing indicated that this information affected the captain’s decision on the go-around. 

This investigation is ongoing, but it suggests, as did the accidents in the early 1990s, that flightcrews are encountering icing conditions for which their aircraft are not suitably designed to handle, and for which their training is inadequate.  Although the FAA received a proposal from the ARAC for an expanded icing envelope to include SLD in 2005, the publication of an NPRM has been delayed numerous times, and the FAA now expects to issue an NPRM in June of this year. 

While there has been progress on the part of the FAA, the NTSB is concerned that the process for incorporating these recommended changes is slow.  In March 2009, 13 years after the NTSB issued the recommendations regarding expansion of icing conditions considered when certifying an aircraft, the FAA decided to form an advisory committee for Part 23 aircraft.  Part 23 airplanes tend to be smaller aircraft such as are used in business jet and air taxi operations.(1)  As of our most recent update at the end of 2009, this advisory committee had not yet been formed or met.  At the current rate, we would not expect these regulatory changes to be in place until almost 20 years after the Roselawn accident.

Although not an in-flight aircraft icing recommendation, the Safety Board has been concerned with the broader issue of excursions due to runway contamination.  Performing landing distance assessments, which assure an adequate safety margin for landing, is another important issue included on the Safety Board’s Most Wanted List.   The recommendation asks the FAA to require operators to incorporate a 15 percent safety margin for landing on contaminated runways and was issued as a result of the NTSB’s investigation of a fatal runway excursion involving Southwest Airlines at Chicago-Midway Airport in December 2005.

When the NTSB issues a safety recommendation with an “urgent” designation, it expects that the action can be completed within one year after the recommendation is issued.  However, in this case, the FAA has only issued guidance and encouraged operators to conduct a landing distance assessment.  The FAA has not made this a requirement and recent investigations have revealed that some of the FAA’s inspectors are not aware the guidance exists.  Since the guidance was issued, the Safety Board has investigated several accidents involving runway overruns on wet or contaminated runways, including Shuttle America flight 6448 in Cleveland; Pinnacle Airlines flight 4712 in Traverse City, Michigan; a Hawker Beechcraft Part 135 flight in Owatonna, Minnesota; and, we are supporting the Jamaican authorities as they investigate the recent American Airlines runway excursion that occurred on December 22, 2009, in Kingston.

Mr. Chairman, this concludes my testimony.  I look forward to answering any questions that you and the members of the Subcommittee may have.

 


Footnote:

1. Part 23 Normal category is Max TOW 12,500 pounds or less, nine seats or less (excluding pilot seats); Commuter category multiengine aircraft may be certified under Part 23 if propeller driven, 19 seats or less (excluding pilot seats) and Max TOW less than 19,000 pounds.


 

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