The Dangers of Airframe Icing and Helicopter Ice Ingestion


Slack Davis Sanger aviation attorneys have specific expertise in investigating and successfully resolving cases in which airframe icing was a significant factor in the crash. The issues related to airframe icing are complex and typically involve questions about piloting procedures, aircraft characteristics, weather and pilot training. Some aircraft, such as the Cessna Caravan, have proven to be more susceptible to airframe icing than other aircraft and are susceptible to sudden loss of control in benign icing conditions.

What is Airframe Icing?
Airframe icing occurs when water droplets freeze on the external surfaces of an aircraft. In general, airframe icing is a potential flight hazard since it adds unintended weight and can significantly disrupt and destroy the functions of the aerodynamic surfaces and degrade performance of the aircraft’s propulsion system. Airframe icing alters the airplane geometry and destroys the intended aerodynamic functions of the wings, tail, ailerons, rudder, elevators and flaps. Airframe icing also affects propellers and significantly reduces engine power by blocking or clogging engine inlets.

Airframe icing can occur while the aircraft is on the ground and frost forms on the airframe. This type of icing contamination can usually be removed on larger aircraft by spraying the aircraft, before take-off, with a de-icing chemical. Frost is removed from smaller aircraft by mechanically cleaning the affected areas.

Airframe icing is more problematic after the aircraft takes flight. When icing occurs in flight the pilot must first recognize the potential hazard and react in a timely and appropriate fashion. Even though the aircraft may be certified to fly in icing conditions and is equipped with a de-icing or anti-icing system, the aircraft’s de-icing or anti-icing systems must be able to prevent or remove sufficient ice such that the functions of the aerodynamic surfaces and the engine are preserved and protected.

Aircraft Certification Issues
Many aircraft are certified to fly in icing conditions. Despite the certification, the aircraft’s actual capability to perform in the icing environment can present serious safety issues. The Cessna Caravan is an example of an aircraft which is very susceptible to loss of control in icing conditions, but which is nonetheless certified for flight in icing conditions. A similar situation was noted in the 1994 crash of American Eagle Flight 4184 near Roselawn, Indiana.

Cessna Caravan 208B
The Cessna 208B Caravan equipped with pneumatic de-icing boots is very susceptible to airframe icing, especially in-flight airframe icing. The Caravan is certified to fly in icing conditions; however documents and testimony obtained by Slack Davis Sanger aviation attorneys in connection with the November 2002 crash of aircraft N514DB near Parks, Arizona, contain substantial evidence that the icing certification of the 208B model was inadequate and does not meet minimum certification standards. Both the National Transportation Safety Board (NTSB), in late 2005, and the Canadian Transportation Safety Board, in early 2006, issued safety recommendations and expressed concerns about the safety of the Caravan flying under icing conditions. But the Federal Aviation Administration (FAA), which has known about the Caravan problem for years, has not taken appropriate action. The NTSB has characterized the FAA’s action, or inaction, on the NTSB’s list of icing safety issues as “unacceptable.”

American Eagle Flight 4184 (Roselawn, Indiana)
On October 31, 1994, American Eagle Flight 4184 crashed near Roselawn, Indiana. The resulting litigation, in which Slack Davis Sanger participated, developed strong evidence that, as designed and certified, the ATR aircraft was susceptible to a loss of control in icing conditions. The control problems faced by the pilots included an aerodynamic phenomena called “control reversal” in which certain aerodynamic characteristics of the aircraft in icing were opposite to what the pilots expected. There was also evidence developed that pointed to a delay in the pilots’ recognition of and failure to appreciate the severity of the icing.

Ice Ingestion

Helicopters and Ice Ingestion

Turbine engines are known for being highly susceptible to ice. It only takes between 20 and 40 grams of ice to cause a complete engine flameout depending on the engine. To put that in perspective, a normal freezer ice cube is approximately 10 grams, so it only takes 2–4 ice cubes to completely shut down the most popular engines used on single engine helicopters. While a number of ice ingestion accidents involve the LTS101, the Turbomeca Arriel engine has also been involved in several ice ingestion accidents.  Some after-market air inlet modifications further increase the risk of ice ingestion accidents because they create water collection points that cannot been seen during a normal pre-flight inspection.

What Happens with Ice Ingestion?

Ice ingestion accidents can occur in two primary ways: first, there is water that enters the air inlet in liquid form then freezes in the inlet; second, ice forms from water vapor due to the venture effect similar to carburetor icing.  In fact, operators are reminded that the FAA issued a Special Airworthiness Information Bulletin (SW-08-03R3) covering this topic. The Bulletin describes procedures for reducing the probability of engine shutdown due to snow and/or ice ingestion.

How Can Ice Ingestion be Avoided?

The FAA has issued a number of precautions that can drastically reduce the possibility of an engine shutdown:

  1. Conduct a thorough preflight weather evaluation while aircraft is still on the ground.
  2. When an aircraft is grounded and its engines are shut down, install engine inlet and exhaust inserts/covers.
  3. Grounded aircraft should refrain from prolonged engine idling/running.
  4. Prior to flight takeoff, conduct a thorough inspection of inlets for ice/snow.
  5. Use de-icing fluid or heated air to remove any ice/snow from inlets; do not scrape the ice away.

When An Aircraft Crashes as a Result of Ice Ingestion, Whose Responsibility Is It?

The key to avoiding those disastrous incidents is to keep moisture out of the air inlet. This solution has been shared far and wide using safety alerts and bulletins. In 2013, Transport Canada issued the warning; Eurocopter has done the same. These companies believe that by calling out the precautions, responsibility for a crash ideally will shift more toward the pilot. Another issue has been raised by Transport Canada regarding the feasibility of a vigilant inspection before every takeoff. Yet some of the Arriel inlets, like the Honeywell LTS101 and the FDC/aerofilters plenum, are designed such that it’s impossible for a pilot to conduct inspection in the most critical areas where ice can form.

Slack Davis Sanger Representative Ice Ingestion Cases

Slack Davis Sanger has handled several accidents involving engine failures due to ice ingestion.  All of these cases have involved Airbus/Eurocopter helicopters.  In some cases the original helicopter was modified with a sand filter, FDC barrier filter, or Soloy engine conversion, which created a new air inlet to mate with the Honeywell LTS-101 engine. Tragically, in every instance the ice caused complete flameout of the engine and a subsequent crash.

Why is Slack Davis Sanger the Best Choice for Airbus Helicopter Crashes?  

Slack Davis Sanger have helicopter accident attorneys with extensive experience in a variety of helicopter crash claims. Many of its attorneys are not only experienced trial lawyers, but also licensed pilots. For example, attorney Ladd Sanger adds an additional level of insight as a helicopter pilot. This kind of hands-on technical knowledge and clear understanding of all facets of the aviation industry are behind many of Slack Davis Sanger’ successful cases. Also, aviation attorney Michael Slack has authored papers and given presentations about how to make air medical services safer. As acknowledged by its mission statement, the firm’s well-rounded attorneys know how to aggressively seek advantageous resolutions for its clients in the shortest time possible.

Slack Davis Sanger aviation lawyers represent passengers and families involved in icing and ice ingestion air crashes. We invite you to contact us to learn more.