Feb 15, 2009

Icing certification envelope

Every model of airliner has been tested and certified to fly into known icing conditions. But as with every other certification parameter, there are set limits and envelopes that the pilots are responsible to know and respect. This burden does not fall exclusively on the pilots.

The certification authorities are responsible to set realistic limits and ensure that the manufacturer's have adequately tested and demonstrated these limits. Manufacturers must properly design and fully test the capabilities of their aircraft, and publish clear limitations, guidelines and procedures for operators to follow. And airlines must properly pass these parameters on to their pilots through Standard Operating Procedures and appropriate training.

Here's an accident from 1994 that will certainly be considered by the accident investigators of Colgan Flight 3047:

American Eagle Flight 4184


The National Transportation Safety Board (NTSB) stated that the probable cause of this crash was the flight into known icing conditions, with the aircraft being operated outside its "icing certification envelope". While the ATR's deicing boots were able to remove ice along the leading edge, it rapidly re-formed behind the boots as runback ice, where it could not be removed. This separated the airflow from the wing's surface and made the aileron control inadequate or non-existent. The ATR family of aircraft has had a history of known and reported control problems in icing conditions. For that reason, the NTSB also mentioned as contributing factors the "inadequate response" on part of the manufacturer and the French DGAC and United States' Federal Aviation Administration aviation authorities to these reports.

Here's a video explaining the limitations of wing de-icing systems and the problems that can occur from prolonged exposures to ice build up...

1 comment:

globalgal said...

I remember the 1994 accident involving the ATR because suddenly the carrier operating regional flights from Houston to my hometown in South Texas moved their ATRs south. I remember how the local community was up in arms because they misinterpreted the media coverage and believed the ATR to be an unsafe aircraft.