New design passenger aircraft must include ice prevention systems that automatically activate or warn the pilots of ice buildup.

Responding to a fatal 1994 regional airline crash in Indiana, the rule “increases safety by not relying on the pilot alone to observe whether the airplane is accumulating ice,” says the Federal Aviation Administration (FAA). While the requirement applies only to new aircraft designs, the FAA said it will consider a rule for existing airplane models.

A flight operated by Simmons Airlines for American Eagle crashed in Roselawn, Indiana, on Oct. 31, 1994, killing all 68 people on board. A ridge of ice had built up on the ATR-72, causing the turboprop to stall after holding at 10,000 feet, the National Transportation Safety Board (NTSB) concluded.

The FAA changed its certification standards for transport category airplanes to require either the automatic activation of ice protection systems or a method to tell pilots when they should be activated.

The new rule requires an effective way to ensure the ice protection system is activated at the proper time. “We’re adding another level of safety to prevent situations where pilots are either completely unaware of ice accumulation or don’t think it’s significant enough to warrant turning on their ice protection equipment,” said FAA Administrator Randy Babbitt.

Under the revised certification standards, new transport aircraft designs must have one of three methods to detect icing and to activate the airframe ice protection system:

• An ice detection system that automatically activates or alerts pilots to turn on the ice protection system;

• A definition of visual signs of ice buildup on a specified surface (e.g., wings) combined with an advisory system that alerts the pilots to activate the ice protection system; or

• Identification of temperature and moisture conditions conducive to airframe icing that would tip off pilots to activate the ice protection system.

The standards further require that after initial activation, the ice protection system must operate continuously, automatically turn on and off, or alert the pilots when the system should be cycled.

The FAA had previously addressed activation of pneumatic deicing boots on many aircraft models by requiring activation of boots at the first sign of ice accumulation. This certification standard applies to all types of ice protection systems, not just pneumatic deicing boots.

The 1994 ATR-72 crash occurred in icing conditions. It prompted the FAA to initiate a review of aircraft inflight icing safety and determine changes that could be made to increase the level of safety.

In May 1996, the FAA sponsored the International Conference on Aircraft Inflight Icing where icing specialists recommended improvements to increase the level of safety of aircraft operating in icing conditions. The FAA reviewed the conference recommendations and developed a comprehensive multi-year icing plan.

The FAA Inflight Aircraft Icing Plan dated April 1997 described various activities the FAA was contemplating to improve safety when operating in icing conditions.

In accordance with the Icing Plan, the FAA tasked the Aviation Rulemaking Advisory Committee (ARAC), through its Ice Protection Harmonization Working Group, to consider the need for ice detectors or other acceptable means to warn flightcrews of ice accretion on critical surfaces requiring crew action. This rule is based on ARAC's recommendations to the FAA.

A notice of proposed rulemaking (NPRM), published in the Federal Register on April 26, 2007 is the basis for this amendment. The comment period closed July 25, 2007.

In the NPRM, The FAA proposed to revise the airworthiness standards for type certification of transport category airplanes to add requirements to ensure the timely activation of an airframe ice protection system (IPS). The FAA also proposed to add requirements to reduce the flightcrew workload associated with operation of an airframe IPS that is manually cycled, and to ensure the Airplane Flight Manual includes IPS procedures for operation.

The first method of ice detection is the use of a primary IDS. A primary IDS usually has two ice detectors. The cost of an ice detector used in this analysis is based on Goodrich Corporation's average price of $6,000 per ice detector for a production airplane. The ARAC Ice Protection Harmonization Working Group provided the FAA with manufacturer cost estimates for system design, system qualification, hardware,
installation, and maintenance.

Assuming the primary IDS has two ice detectors, the FAA estimates the average cost for a primary IDS to be about $485,000 per certification, $12,000 ($6,000 x 2) for the hardware and $2,500 for the installation, or $14,500 ($12,000 + $2,500) per airplane.

The second method of ice detection is the use of an advisory IDS along with visual cues. The major difference between a primary and an advisory IDS is that the primary is the principal means to determine when the airframe IPS should be activated and has two ice detectors. In contrast, an advisory IDS is a backup to the flight crew and has only one ice detector.

The FAA estimates that the average cost for an advisory IDS is $447,500 per certification, $6,000 for the hardware and $1,250 for the installation, or $7,250 ($6,000 + $1,250) per airplane.

The third method of ice detection is a definition of conditions conducive to airframe icing that will be used by the flight crew to activate the airframe IPS. This definition will be included in the Airplane Flight Manual. There are no costs imposed on the airplane manufacturers with this option.

The least cost alternative is to activate the airframe IPS whenever the airplane is operating in conditions conducive to airframe icing based on a specific air temperature threshold and the presence of visible moisture. Since there are no additional certification or production costs to manufacturers through this alternative, The FAA determined there are no costs associated with such compliance.

“The FAA has determined that this final rule has benefits that justify its minimal costs. The FAA is adopting this final rule because accidents and incidents occurred where the flight crew did not operate the airframe IPS in a timely manner and because of concerns over the flight crew workload required to operate an airframe IPS that the flight crew must manually cycle.

“The final rule addresses these concerns by ensuring that flight crews are provided with a clear means to know when to activate the airframe IPS and by reducing the workload associated with an airframe IPS that operates cyclically. The safety benefit of this final rule is that it will improve the level of safety of new airplane designs for operations in icing conditions,” the aviation agency stated.

Since 1994, the FAA has issued more than 100 airworthiness directives to address icing safety issues on more than 50 specific aircraft types. These orders cover safety issues ranging from crew operating procedures in the icing environment to direct design changes. It has also changed airplane flight manuals and other operating documents to address icing safety, and issued bulletins and alerts to operators emphasizing icing safety issues.

The FAA is also developing a proposed rule to address supercooled large drop icing, which is outside the icing envelope considered by the current icing certification requirements. The proposed rule would improve safety by taking into account supercooled large-drop icing conditions for transport category airplanes most affected by these icing conditions, mixed-phase and ice-crystal conditions for all transport category airplanes, and supercooled large drop, mixed phase, and ice-crystal icing conditions for all turbine engines. An economic analysis is currently being prepared.

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