On December 29, 2006, about 0200 mountain standard time, a Beech B-99, N99TH, piloted by a commercial pilot, sustained substantial damage when it impacted the ground during an instrument approach to runway 32 at the Rapid City Regional Airport (RAP), Rapid City, South Dakota. The 14 CFR Part 135 cargo flight was operated by Alpine Aviation as Alpine flight 408 (AIP408) and was in night instrument meteorological conditions on an instrument flight rules flight plan. The pilot received minor injuries. The flight originated from the Pierre Regional Airport, Pierre, South Dakota, about one hour prior to the accident.

In a written statement, the pilot reported that he elected to use the 7 nautical mile DME arc of the VOR Runway 32 approach to transition to the ILS approach and he used an altitude of 4,700 feet for the transition. He stated that after turning inbound on the final approach course he performed the before landing checklist, set the gear and flaps, and reported inbound on the common traffic advisory frequency. He stated that less than five minutes later, he felt a "sharp blow", added full power, and pitched the nose up but the recovery attempt was unsuccessful.

The pilot held a commercial pilot certificate with single engine land, multiengine land, and instrument airplane ratings. He also held a second class airman medical certificate issued on April 12, 2006. The medical certificate listed no limitations.

The pilot reported having a total of 3,652 hours of total flight experience, including 2,895 hours in the same make and model as the accident airplane. He listed 222 hours and 74 hours of flight experience in the preceding 90 and 30 days, respectively.

The airplane was a Beech model B-99, twin-engine airplane powered by two Pratt and Whitney PT6A turbopropeller engines. Each engine was rated 550 shaft horsepower. The airplane's maximum gross weight was listed as 10,900 pounds. The airplane was maintained in accordance with an approved airworthiness inspection program. The airplane had accumulated 39,795 hours time in service as of the airplane's most recent inspection performed on November 8, 2006.

At 0211, the reported weather at RAP was: wind 340 at 18 knots, gusting to 25 knots; visibility 2.5 miles; broken ceiling 1,300 feet; temperature -3 degrees Celsius; dew point -6 degrees Celsius; altimeter setting 30.35 inches of Mercury.

The ILS runway 32 approach to RAP provided lateral and vertical guidance to aircraft approaching for landing. The approach chart did not depict a DME arc as an approved method of intercepting the ILS final approach course. The ILS runway 32 approach chart depicted the initial approach fix (IAF) as the Ranch locator outer marker. A procedure turn, at a minimum altitude of 5,500 feet, was depicted as the method for establishing an inbound course after flying outbound from the IAF. The chart depicted the final approach glide path altitude at the Ranch LOM, 4.6 nautical miles from the airport, as 4,688 feet.

Flight inspection reports for the RAP ILS runway 32 approach were obtained. The inspections performed on July 27, 2006, and February 28, 2007, listed satisfactory results for localizer and glideslope operation.

According to communications transcripts, AIP408 checked on frequency with the Denver Air Route Traffic Control Center at 0112. At that time, AIP408 reported the airplane's altitude as 10,000 feet. The air traffic controller acknowledged and then provided AIP 408 with the current weather conditions at RAP, which included an altimeter setting of 30.31 inches of mercury. At 0118, AIP408 was cleared for the ILS Runway 32 approach to RAP. The flight was instructed to cross the initial approach fix at an altitude of 6,000 feet or higher. At 0127, air traffic control advised AIP408 that radar contact was lost and requested that the AIP408 report reaching 6,000 feet. At 0129 AIP408 reported reaching 6,000 feet. Denver ARTCC then advised AIP408 of approval to change to the airport advisory frequency, which AIP408 acknowledged. No further transmissions were received from AIP408 by the Denver ARTCC.

RAP is located an elevation of 3,204 feet and was equipped with two intersecting runways. Runway 5/23 was 3,601 feet by 75 feet, and runway 14/32 was 8,701 feet by 150 feet. Five instrument approach procedures were listed for RAP including the ILS/LOC runway 32, and the VOR/TACAN runway 32 approaches. RAP is equipped with a control tower; however, at the time of the accident the control tower was not in operation.

The airplane impacted the ground about 7 miles from RAP at an elevation of about 3,200 feet. Examination of the airplane subsequent to the accident revealed no anomalies with respect to the airframe, control systems, or engines.

The airplane's number one altimeter had a Kohlsman setting of 30.44 inches of mercury. The number two altimeter's Kohlsman setting was not recorded; however, the setting did not match the current altimeter setting reported at the time of the accident. The airplane's altimeters were removed and their readings compared to a master altimeter at a certified repair station. The number one altimeter read 360 feet high, and the number two altimeter read 10 feet low when compared to the master altimeter's reading. No determination was made as to whether the number one altimeter's error existed prior to impact. The pilot did not report any pre-flight discrepancies with regard to the airplane's altimeters. No other flight instrument anomalies were identified.

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