NTSB Identification: WPR11FA170
14 CFR Part 91: General Aviation
Accident occurred Saturday, March 19, 2011 in Butte, MT
Probable Cause Approval Date: 04/20/2012
Aircraft: CESSNA T310R, registration: N4914A
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

Shortly before embarking on the flight, the instrument-rated pilot filed an instrument flight plan and checked the weather using a computer-based filing system. At that time, the destination airport was reporting visual meteorological conditions, with similar conditions forecast for the planned arrival time. The pilot did not list an alternate airport in the flight plan. About halfway through the flight, the pilot contacted the air traffic controller responsible for the destination airport’s airspace. By that time, the weather conditions at the destination had deteriorated, with reports of snow and fog and visibility below the instrument approach minimums. The controller provided updated weather information and asked the pilot if he wanted to continue with the initial approach. He responded that he did and that he would divert to an alternate airport if necessary. The pilot was then cleared for the approach, and the airplane began to descend toward the initial approach fix (IAF).

Shortly thereafter, a scheduled air carrier airplane destined for the same airport contacted the same controller. The controller relayed the weather information, and the crew of that airplane responded that they would delay the approach to see if the weather conditions improved. About that time, the accident airplane reached the IAF and began the approach. The air carrier pilot then requested and received approval to divert to an alternate airport due to the weather conditions. The accident pilot most likely did not hear this exchange because he had switched to the airport frequency. Due to limitations in radar coverage, the air traffic controller was not able to see the airplane once it had descended to the approach altitude.

About 4 minutes after the air carrier airplane began to divert, the accident pilot reported that he was performing a missed approach. The controller provided missed approach instructions and asked for the pilot's intentions. The pilot read back the instructions but did not state his intentions. The controller asked if he would like to divert to the alternate airport, and, after a series of delayed and partial responses from the pilot, a call of "Mayday Mayday" was heard on the controller's frequency. For the next 35 minutes, the controller unsuccessfully attempted to contact the pilot. During that period, an air medical flight also canceled a landing approach into the airport due to deteriorating weather conditions. Multiple witnesses reported the sounds of a loud, low-flying airplane northwest of the airport about the time of the landing attempt. The witnesses reported the sudden onset of a gusting wind, heavy snow, low visibility, and ice accumulations during that period.

The airplane wreckage was located a few miles from the witnesses, about midway between the airport and the missed approach hold location. The wreckage distribution and flight instrument readings were indicative of a high-speed, steep nose-down, left-turning descent into the ground, with a heading almost opposite the direction of the missed approach route. Engine instrument indications, and both the engine and propeller damage signatures, were consistent with the engines producing similar amounts of power at the time of impact. The airplane was equipped with instruments and systems required for flight in instrument meteorological conditions (IMC) and flight into known icing. Additional equipment included an autopilot and a global positioning system (GPS) navigation and communication transceiver capable of receiving and displaying current weather information via satellite. Impact damage prevented a determination of the operational status of those systems.

Available ground-based radar tracking data indicated smooth heading and altitude changes and minimal altitude deviations prior to the pilot being cleared for the approach, consistent with autopilot use. According to the prior owner of the airplane, the autopilot was susceptible to becoming disengaged during turbulent conditions, and, as such, it is possible that at some point during the approach the pilot was forced to revert to flying the airplane manually. Under such circumstances, the pilot's workload would have rapidly increased. Additionally, the likely accumulation of ice on the airplane's airframe would have reduced flight performance and added to his workload as he attempted to monitor the ice accumulation and operate the deice system. The pilot had recently purchased the airplane and likely had minimal solo experience flying it in IMC.

The airplane was about 2 months overdue for its annual inspection, and 12 months overdue for its transponder, static, and altitude reporting systems check. However, postaccident examination of the airframe remnants did not reveal any failures or malfunctions which would have precluded normal operation. The engines exhibited indications of wear that would have resulted in a gradual reduction in engine power over its life, rather than a sudden loss of power.

Although the severe weather conditions were not forecast, the pilot was accurately advised of the deteriorating conditions by the controller prior to the approach, and he would have had access to airport terminal reports via the airplane's radio and his GPS navigation system. The lack of a filed alternate airport indicates that the pilot was not prepared for the severity of the weather conditions. The airplane was carrying ample reserves of fuel, with enough to return to the departure airport if necessary.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's loss of airplane control during the missed approach for undetermined reasons. Contributing to the accident was the rapid and unforecast deterioration of the weather conditions to below the landing minimum and the pilot's decision to attempt the approach despite his knowledge of those conditions.

Full narrative available

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