The Federal Aviation Administration (FAA) is proposing to amend the airworthiness standards for transport category airplanes certificated for flight in icing conditions and would apply to new designs. The FAA wants to specify an automated IPS (Ice Protection System) that not only warns but acts. The Agency says such systems would remove any question of when pilots are required to activate such measures. By being automated, proactive and pre-emptive, needless accidents could be avoided. It is a laudable exercise that up until now has been frozen technical limitations and deficient design, according to Air Safety Week, RAN's sister publication, which, this week, produced an in-depth analysis of the proposed rule. Comments are due July 25.
This proposed rule is based on Aviation Rulemaking Advisory Committee (ARAC) recommendations to the FAA from the ARAC Ice Protection Harmonization Working Group or IPHWG). ARAC was asked to advise on ice detectors or other acceptable means to warn flightcrews of ice accretion on critical surfaces requiring crew action. Under existing regulations, the certification rules require that: ‘‘the airplane must be able to operate safely in the continuous maximum and intermittent maximum icing conditions of appendix C. Specifically addressed are operations in icing conditions that might adversely affect safety and installation of certain types of ice protection equipment and wing illumination equipment. Surprisingly, neither the operating regulations nor the certification regulations require a means to warn flightcrews of ice accretion on critical surfaces requiring crew action.
The benchmark accidents that are often cited as classic examples of icing perils are once again::
•The ATR 72 accident in Roselawn, Indiana on October 31, 1994, where 68 people died. The accident airplane crashed during a rapid descent after an uncommanded roll excursion while operating in icing conditions. The National Transportation Safety Board recommended that the FAA require a means for flight crews to positively determine when they are in icing conditions that exceed the limits for aircraft certification.
• The Embraer Brasilia accident near Monroe, Michigan, on January 9, 1997, where 29 people died. The accident airplane crashed while operating in icing conditions. The flight crew may not have activated the airframe ice protection system. The NTSB recommended that the FAA require manufacturers and operators to revise their manuals and training to emphasize that leading edge deicing boots should be activated as soon as the airplane enters icing conditions.
What the FAA does not address in this NPRM are the aspects covered by the ARAC which are most problematic and ,thus far, defy easy solutions:
• Part 121 recommendations to address activation of ice protection systems.
• Part 121 recommendations to require certain airplanes to exit icing conditions.
• Part 25 and 33 recommendations to address operations in supercooled large droplet, mixed phase, and glaciated icing conditions.
According to the NPRM, these issues may be the subject of further rulemaking. The subject of supercooled large droplets (SLD) -- rain-ice or freezing rain -- is the most vexing. Rather than broad-brush the whole subject however, the NPRM concentrates upon the IPHWG’s review of icing events and the accidents and incidents where the flight crew was either completely unaware of ice accretion on the airframe, or was aware of ice accretion, but judged that it was not significant enough to warrant operation of the airframe ice protection system. The IPHWG concluded (and recommended to the FAA) that flight crews must be provided with a clear means to know when to activate the IPS.
The FAA has, for certain airplane types, issued directives as to exactly when pilots should activate anti- and de-ice systems - in particular, deicing boots but concedes that darkness, high workload and the transparency of clear ice may make it difficult for pilots to determine the need. It also recognizes that the difficulties of observing ice accretions are applicable to any IPS that relies on the flight crew’s observations for activating the system, not just pneumatic deicing boots. The IPHWG concluded that installing a device to alert the flight crew to activate the IPS would be an improved means to address these situations for future airplanes. A primary ice detection system would be one acceptable means. An advisory ice detection system, in conjunction with substantiated visual cues, would also be an acceptable means. For a complete report on the issues surrounding primary ice detection systems and an advisory system as well as technology advancement include the use of lasers to rid the aircraft of ice is in the May 7 issue of Air Safety Week.