CHI04LA085On March 8, 2004, at 2155 central standard time, a Cessna 172R, N105FS, operated by Wisconsin Aviation, piloted by a certified flight instructor (CFI), was substantially damaged following an in-flight collision with terrain as the CFI initiated a missed approach at the Dubuque Regional Airport (DBQ), Dubuque, Iowa. The 14 CFR Part 91 instructional flight was operating on an Instrument Flight Rules (IFR) flight plan at the time of the accident. Instrument meteorological conditions prevailed. The CFI, dual student and passenger reported minor injuries. The flight departed the Des Moines International Airport (DSM), Des Moines, Iowa, at 2028 with an intended destination of Dane County Regional Airport-Truax Field (MSN), Madison, Wisconsin.
In his written statement, the CFI reported that the flight encountered light rime icing at 5,000 feet mean sea level (msl) as it approached Cedar Rapids, Iowa. Initially he elected to climb in an attempt to avoid the icing conditions, however, at 7,400 feet msl the aircraft's climb performance had deteriorated significantly. He then decided to descend and was cleared to 4,000 feet msl. The flight subsequently "broke out of [the] clouds at 4,700 [feet] msl and leveled off at 4,000 [feet msl]. The CFI estimated that 1/4 inch of rime ice had accumulated on the wing leading edges and struts at that point.
The CFI stated that due to the icing encountered he decided to divert to DBQ in order to remove the ice from the aircraft and evaluate the weather conditions. He noted that the Automatic Terminal Information Service (ATIS) was reporting visibility at 5 statute miles (sm) in mist, scattered clouds at 600 feet above ground level (agl), and broken clouds at 3,400 feet agl.
The CFI reported that he requested and was cleared for a visual approach. He noted that once they made visual contact with the airport he started a descent for the runway. He stated as they "got over the runway . . . the aircraft moved to the right side of the runway for an unknown reason." He continued: "I thought about landing on [runway] 31 but did not like that idea so I maneuvered the aircraft back over runway 36."
The CFI noted that the aircraft was not in a position to land and elected to execute a missed approach. He stated: "I applied full power and raised the nose to start a climb. I then banked the aircraft to the left to circle back around for landing. At this point the aircraft bucked and shook as if it was stalling. I lowered the nose to stop the stall and noticed the ground coming up quickly. I tried to slow the descent but the aircraft continued descending and impacted the ground."
The passenger located in the right-rear seat reported that the CFI was having difficulty getting aligned with the runway for landing due to "strong winds [and] perhaps the ice on the wings." He reported that as the aircraft entered a turn it began "plunging" toward the ground and subsequently impacted the terrain with the left wing and the nose.
A DBQ airport employee reported witnessing the accident aircraft approach the airport. He stated that he heard the pilot report on final approach for runway 36. He noted that he then saw the lights of the aircraft, which appeared to be flying from west to east, almost above runway 13. He estimated the aircraft's altitude as 100 feet agl "as if [it was] on a missed approach."
The witness recalled that the aircraft's lights seemed to rock back and forth in an "abnormal manner." He stated: "Once toward the end of the runway, around taxiway Bravo and runway 31, I saw the lights seem to dip to the left as if in a turn. I looked out the door to see if I could see if the aircraft had entered the traffic pattern, I saw and heard nothing."
The wreckage was subsequently located in the grass area between runway 31 and taxiway Alpha. The aircraft was lying on its left side, supported by the left wing, which was bent upward approximately 45-degrees. The right wing was separated and located about 10 feet from the left wing tip. Initial impact appeared to be approximately 100 feet northwest of the wreckage location. Ground impact marks indicated that the direction of travel was from the northwest to the southeast; roughly parallel to runway 13.
According to the DBQ Operations Supervisor who was on-scene shortly after the accident, all leading edge surfaces including the horizontal and vertical stabilizers, as well as the radio antennas exhibited ice accumulation. He estimated the thickness as 5/16 - 3/8 inch.
The Area Forecast for the eastern one-third of Iowa specified broken ceilings at 3,500 feet msl with cloud tops to 14,000 feet msl. The forecast noted that ceilings may occasionally be as low as 1,500 feet msl and visibilities 4 sm in light snow.
An AIRMET for icing conditions was in effect for occasional moderate rime or mixed icing in clouds and/or precipitation from the freezing level to 14,000 feet msl. The freezing level was forecast to be between the surface and 4,000 feet msl.
Pilot reports for in-flight icing were on file prior to the accident aircraft's departure from DSM. At 1640, moderate mixed icing was reported 20 miles west of MSN during descent between 10,000 feet msl and 7,000 feet msl. At 1913, moderate mixed icing was reported 30 miles north of Waterloo at 7,000 feet msl. And at 1940, light rime icing was reported 20 miles west of MSN between 6,000 feet msl and 8,700 feet msl.
The routine aviation weather report (METAR) for DBQ, recorded at 2155, was 1-1/4 sm visibility in light snow and mist, few clouds at 300 feet agl, broken clouds at 600 feet agl, and overcast clouds at 3,200 feet agl. Winds were from 030 degrees at 6 knots.
The Cessna model 172R information manual states that flight into known icing conditions is prohibited.
Federal Aviation Administration (FAA) Advisory Circular (AC) 61-23C, Pilot's Handbook of Aeronautical Knowledge, states that in-flight "ice formation will alter the shape of the airfoil and adversely affect all aspects of airplane performance and control. As the ice forms on the airfoil, especially the leading edge, the flow of air over the wing is disrupted. This disruption of the smooth airflow causes the wing to lose part or all of its lifting efficiency."
FAA AC 61-67C, Stall and Spin Awareness Training, states that "any contamination or alteration of the leading edge caused by factors such as . . . ice can significantly alter the aerodynamic characteristics of the wing." It goes on to note that an "aerodynamic stall may occur with little or none of the usual cues in advance of the stall or at the occurrence of stall."
ouch!
