The flight instructor reported that, during a long cross-country flight, they encountered deteriorating weather conditions, and in order to remain VFR, altered course and destination. En route, while approaching a ridge line, he "noticed that [the airplane's] airspeed started to drop toward 65 miles an hour". He added that "[he] thought that maybe [they] were picking up carburetor ice and [he] reached for the carburetor heat and pulled it out". The student pilot reported that after the flight instructor stated, "watch your airspeed", he looked at the Revolutions Per Minute (RPM) gauge and noted that it was indicating 1800-1900 RPM. He added that, the flight instructor took over the flight controls and the airplane impacted the top of the ridge. A review of multiple weather observation stations, located around the four corners of the accident site, revealed similar conditions, temperature 55°F, and dew point 43°F. Review of the Federal Aviation Administration Carburetor Icing Chart for the given temperature and dew point revealed that the conditions were conducive to "serious icing at cruise power". (For more information see Special Airworthiness Information Bulletin CE-09-35 in the public docket.) The airplane sustained substantial damage to the right wing.