SEA04LA038

The flight instructor and non-instrument rated private pilot departed Pocatello, Idaho, on an instrument trainer for the private pilot. The instructor had filed an IFR flight plan to Rexburg, Idaho, and acknowledged an awareness of an AIRMET advising of occasional moderate rime to mixed icing-in-clouds below 16,000 feet. En route to Rexburg the aircraft entered a holding pattern at Idaho Falls, Idaho, during which it picked up what the private pilot described as "light" ice and the instructor characterized as a "trace" during the hold. Both pilots reported removing ice from the aircraft following the landing at Rexburg. The student obtained an updated weather brief where icing was again discussed and he filed an IFR flight plan from Rexburg back to Pocatello. The student and instructor then departed Rexburg for Pocatello. During the climb the aircraft began picking up ice and the instructor initially attempted to divert to Idaho Falls but upon breaking out of the clouds and noting the Rigby, Idaho, airport passing abeam, changed his intended landing site to Rigby. During the student's course reversal back toward Rigby the aircraft began descending rapidly eventually stalling prior to ground impact in a snow-covered agricultural field. The Cessna 172N was not equipped with any anti-icing or de-icing equipment with the exception of carburetor heat. The Pilot's Operating Handbook (POH) for the aircraft cautions that "Flight into known icing conditions is prohibited" both as a placard within the aircraft and as a flight limitation.

History of flight

On January 28, 2004, approximately 1020 mountain standard time, a Cessna 172N, N734CB, registered to an individual, operated by Avcenter, Inc., and being flown by a commercial flight instructor and a private pilot, sustained substantial damage during a loss of control and in-flight collision with terrain near Rigby, Idaho. Both pilots suffered serious injuries. Instrument meteorological conditions prevailed and an IFR flight plan from Rexburg to Pocatello, Idaho, had been filed. The flight, which was instructional, was operated under 14CFR91, and had originated from Pocatello (PIH), Idaho, approximately 0900.

The flight instructor reported that the left seat (private) pilot was undergoing training toward his instrument rating. He reported that he and the student "...called the tower (at Pocatello) to ask if my company (Skywest) received any icing on the climb out of PIH, which was a negative...." The two pilots departed PIH and flew a VOR approach into Rexburg, Idaho, their destination, after holding for 20 minutes at Idaho Falls (IDA). The instructor reported that "...We landed with a trace of ice on the aircraft" and "we cleaned the aircraft off..." (refer to attached NTSB Form 6120.1/2).

The student then filed an IFR flight plan from Rexburg back to Pocatello and the instructor reported that "...He got the weather and we departed at approx[imately] 10:00 am...." After departure the aircraft was cleared to 8,000 feet and the aircraft began picking up ice. Unable to reach 8,000 feet a request for 7,000 feet was cleared and the instructor "...requested vectors for the localizer into IDA [Idaho Falls airport]...." A descent was initiated and the instructor reported breaking out at 5,200 feet as the aircraft was passing the Rigby airport (refer to CHART I). The instructor elected to attempt a landing there. He reported "...Into the turn, I could tell the aircraft was not going to fly, so elected to land it into a field. At ground effect I reduced the power, and the tail stalled, and we nosed in...."

The private pilot reported he and the instructor departed Pocatello on the instrument trainer and that he "...was under the hood for simulated IFR conditions...." The aircraft encountered IFR conditions and was required to hold at IDA, and after one complete circuit of the holding pattern the student then executed the approach into Rexburg landing without incident. He reported, "...while on the ground at Rexburg we removed ice from the airplane that had accumulated during our hold at Idaho Falls..." and the instructor then boarded the aircraft "...while I finished up the ice removal. It was on both the front and rear wings and the propeller..."(refer to attached NTSB Form 6120.1/2).

The private pilot reported that they departed Rexburg with a climb to 8,000 feet and a clearance direct to PIH and he did not have the hood on as they were in IFR conditions. He continued reporting, "...My speed was quite slow. Between 60-70kts, which did cause me concern and prevented me from climbing at a normal rate...." Unable to climb to 8,000 feet the altitude was amended to 7,000 feet but upon reaching that altitude the aircraft began to lose altitude. The instructor then requested a clearance for the ILS approach into Idaho Falls and the private pilot reported, "...that the 10 miles we had to go to Idaho Falls was not going to be possible...." The instructor then noted the Rigby airport advising the private pilot to land there and "...I turned to the left...." The private pilot estimated the altitude as 6,500 feet and reported "...When I turned left the plane would not level out again and we seemed to be descending at a greater rate at this point...." He remembered the initial impact but reported having a poor recollection of events after that.

The aircraft crashed in an open, agricultural, snow-covered field approximately one nautical mile south of the Rigby-Jefferson County airport. Local law enforcement personnel and a representative from the Operator who drove up from Pocatello shortly after the accident reported significant amounts of ice adhering to the aircraft's wing leading edges (refer to graphic images 1 through 5).

Personnel information

The flight instructor possessed a commercial pilot certificate with airplane single-engine, multi-engine and instrument ratings. He also possessed a flight instructor's certificate with airplane single-engine and instrument ratings. He reported a total of 4,365 hours of flight experience of which 601 were in the Cessna 172 and 2,701 hours were in multi-engine aircraft. Of the 1,905 hours of pilot-in-command time logged, 601 hours were logged in the Cessna 172. He also reported a total of 1,029 hours as flight instructor of which 509 were in the Cessna 172. His most recent (equivalent) biennial flight review was conducted on October 23, 2003, in the Embraer EMB-120 aircraft. He held a first class medical certificate, which was conducted on April 17, 2003, with no restrictions or waivers.

The student pilot possessed a private pilot certificate with an airplane single-engine land rating. He reported a total of 130 hours of flight experience of which 100 hours was in the Cessna 172, 90 as pilot-in-command. His most recent biennial flight review was conducted on August 1, 2003, in the Cessna 172 aircraft. He held a third class medical certificate, which was conducted on December 10, 2002, with the restriction the he must wear corrective lenses.

Aircraft information

The Cessna 172N was not equipped with any anti-icing or de-icing equipment with the exception of carburetor heat. The Pilot's Operating Handbook (POH) for the Cessna 172N cautions that "Flight into known icing conditions is prohibited" both as a placard within the aircraft and as a flight limitation in Section 2 (refer to Attachment POH-I).

Meteorological information

The special aviation weather observation taken at Fanning Field (IDA), Idaho Falls, Idaho, for 1026 on the morning of the accident reported the following conditions.

Winds from 200 degrees magnetic at 21 knots, visibility 10 statute miles, ceiling 500 foot overcast, temperature/dew point 1/0 degrees Celsius respectively, altimeter 30.00 inches of Mercury, and peak wind from 200 at 26 knots at 1026.

Fanning Field lies 9 nautical miles bearing 206 degrees magnetic from the accident site and the station elevation is 4,740 feet above mean sea level (MSL).

Upper air soundings from Boise, Idaho, and Riverton, Wyoming, were reviewed, and interpolated data indicated that the Lifted Condensation Level (LCL, i.e. cloud base) was 1,630 feet above ground with cloud tops approximately 13,000 feet. The soundings supported light to moderate rime icing-in-clouds and in-precipitation from the surface to 13,000 feet as well as a mixture of snow, freezing rain, and sleet (refer to attached Weather Study).

A pilot report from an aircraft (unknown type) over IDA at 1050 local time and 8,000 feet MSL reported moderate mixed icing from 5,300 feet to 8,000 feet. A pilot report from a Cessna 402 over IDA at 1053 local time and descending reported sky overcast at 5,300 feet MSL and tops at 8,000 feet MSL with moderate mixed icing in clouds (refer to attached Weather Study).

Several AIRMETs (Airman's Meteorological Information) were in effect in the area of the accident. AIRMET Zulu advised of occasional moderate rime to mixed icing-in-clouds and in precipitation below 16,000 feet (refer to attached Weather Study).

The investigator in charge reviewed a rerecording of two telephonic communications with the Boise Automated Flight Service Station (AFSS), which transpired on the morning of the accident. The first took place between Boise AFSS and the flight instructor about 0725-0730. An IFR flight plan was filed however, no weather briefing information was provided. The AFSS specialist asked the pilot if he was awar