THE US FEDERAL Aviation Administration plans to require manufacturers of 26 regional-turboprop types to test their aircraft for susceptibility to large-droplet icing, suspected to have caused the October 1994 crash of an American Eagle ATR 72.
The FAA wants the testing completed by the start of the next US icing season in November. Ideally, the agency wants manufacturers to perform flight tests similar to those conducted by ATR, which determined that super-cooled large-droplet icing could result in un-commanded roll.
The US Air Force Boeing NKC-135A icing tanker used for the ATR tests is due to be retired on 1 June, however, and the FAA has asked the US Air Force to delay decommissioning the aircraft. The USAF has reportedly made another proposal to test the 26 aircraft types identified by the FAA.
The FAA wants large-droplet icing tests conducted an all turboprop-aircraft types in scheduled-airline service, which have manual flight-controls and pneumatic de-icing. High-speed taxi and icing-tunnel tests are possible alternative means of testing the aircraft, the FAA says.
"This is not a certification issue," emphasises John Dow, of the FAA's aircraft-certification service. "The objective is to ensure there is no unsafe condition for inadvertent encounter [of super-cooled large-droplet icing]." Flight tests would allow manufacturers to develop procedures to enable crews to identify and escape the icing conditions.
The FAA will complete a study of super-cooled large-droplet icing in July, Dow says, and will then consider whether it is practical to require aircraft certification for operation in such conditions.
While ATR was able, in the first series of tanker tests, to induce the ice formation believed to have caused the ATR 72 crash, it was unable to repeat this on a second series of flights conducted to test enlarged de-icing boots. The manufacturer has subsequently observed similar icing during certification tests of its ATR 42-500, but only by deliberate prolonged exposure of the aircraft to suitable weather conditions.
Source: Flight International
