NTSB finding was that misconfiguration was a key component of the crash. Doesnt mean that the icing wasnt a major factor and that corrections werent called for. However the full deployment of the flaps and subsequent overspeeding/retraction directly caused the crash. I thought recommended procedures anytime ice was observed was to disengage AP and fly the approach manually. Even GA pilots are taught you never engage flaps with visible ice on the leading wing edges? I know U've got thousands of hours in all kinds of stuff...from the comparatively little I know it sure seems like some fundamental errors...assuming AP was engaged up till final.
I'm sorry
Humble, I don't want to come accross as "I have xxxx hours, u don't I know shut up". I love reading what others have to offer even if it's the intercontinental missile theory. I just like to see people here get their ideas/fact straight about aviation.
Here's the NTSB report you are talking about :
http://www.bluecoat.org/reports/NTSB_96_Roselawn_ATR.pdf ... There's no mention of "full flpas, nor misconfiguration was key". The flaps 15 did cause ice to accumulate beyond the boots, but nothing wrong having them there anyway.
3.2 Probable Cause
The National Transportation Safety Board determines that the probable causes of this accident were
the loss of control, attributed to a sudden and unexpected aileron hinge moment reversal that occurred
after a ridge of ice accreted beyond the deice boots because: 1) ATR failed to completely disclose to
operators, and incorporate in the ATR 72 airplane flight manual, flightcrew operating manual and
flightcrew training programs, adequate information concerning previously known effects of freezing
precipitation on the stability and control characteristics, autopilot and related operational procedures
when the ATR 72 was operated in such conditions; 2) the French Directorate General for Civil
Aviation’s (DGAC’s) inadequate oversight of the ATR 42 and 72, and its failure to take the necessary
corrective action to ensure continued airworthiness in icing conditions; and 3) the DGAC’s failure to
provide the FAA with timely airworthiness information developed from previous ATR incidents and
accidents in icing conditions, as specified under the Bilateral Airworthiness Agreement and Annex 8
of the International Civil Aviation Organization.
Contributing to the accident were: 1) the Federal Aviation Administration's (FAA’s) failure to ensure
that aircraft icing certification requirements, operational requirements for flight into icing conditions,
and FAA published aircraft icing information adequately accounted for the hazards that can result
from flight in freezing rain and other icing conditions not specified in 14 Code of Federal Regulations
(CFR) Part 25, Appendix C; and 2) the FAA’s inadequate oversight of the ATR 42 and 72 to ensure
continued airworthiness in icing conditions.
3.1 Findings
1. The flightcrew was properly certified and qualified in accordance with applicable regulations
to conduct the flight.
8. The flightcrew’s actions would not have been significantly different even if they had received
the available AIRMETs.
9. The flightcrew’s actions were consistent with their training and knowledge.
37. The flightcrew’s failure to increase the propeller RPM to 86 percent and activate the Level III
ice protection system in response to the 1533:56 caution alert chime was not a factor in the
accident.
Even GA pilots are taught you never engage flaps with visible ice on the leading wing edges? I never flew anything big, nor a jet, so I have limited knwoledge. All I know with boots is the planes I currently fly for my cargo airline, being the lil C402B that has boots, and a 16,000 lb turboprop with boots. Nor the FAA directives to us, our company SOP nor the flight manual prohibit from using flaps in icing.
There is an excellent NASA video about flaps in icing. You have two types of icing, the "regular icing" that accumulates on the plane, kills your airflow & add weight. In this type, the plane will stall the "regular way", due to those factors, u are advised not to land full flaps in case of you not having enought power available to maintain flight.
The other type is the tricky one, kind of called "tail icing" by some. This one is caused by changing the angle of attack/ airflow due to flaps extention. This type of icing will cause the nose to go down like a regular stall, BUT any attempt of typical remedy by the pilot by reducing the angle of attack by putting the nose down will INCREASE the stall. To correct that NASA states to "undo what you have done".
On a side note about icing, I did encounter severe icing in both the Turbo prop and the 402. In the Metro, at 17000ft the IAS went down from 180 to 130, but I could maintain flight there. In the 402, a couple of times each winter we can't maintain altitude. Once this year I droped from 13,000 to 9,500, ice accumulated from clear wings to not flying in less than 2 min. The other time, I was 10000, diped down to 9000. Sucks when the MEA is 10K
Those 402B have the tiptanks, those are the killers. I noticed the 402C without the tiptanks have significant improvement in the ice.
About those boots, on my planes they are powered by vaccum pressure like my instruments but at 18 PSI, they are ususally rendered ineffective by multiple tiny cuts/holes in the boots.
Dawger already covered all that ... rock on dude ... I'm going back to honoring Vday I guess 
