On October 17, 2004, approximately 2214 mountain daylight time, the main landing gear of a Beech 99A, N955AA, struck a building during an instrument landing system (ILS) approach to runway 10L at Billings Logan International Airport, Billings, Montana. The commercial pilot executed a missed approach, and the flight proceeded to Great Falls, Montana. During the landing roll at Great Falls International Airport, the right main landing gear collapsed. The airplane was registered to and operated by Alpine Air Inc. of Provo, Utah. The pilot, the sole occupant, was not injured, and the airplane sustained substantial damage. Instrument meteorological conditions prevailed, and an IFR flight plan was filed for the Title 14 CFR Part 135 air taxi flight. The flight initially departed from Great Falls at 2130 with an intended destination of Billings.

According to information provided by the Billings Air Traffic Control Tower, the flight was cleared for the ILS RWY 10L approach to Billings at 2208:23. At 2211:44, the controller issued a low altitude alert, stating the flight "should be at 5700." At 2212:03, the controller reported the flight was 1 nautical mile (nm) outside Saige (the initial approach fix). At 2213:58, the controller issued another low altitude alert. The pilot "reported out of 3,800 and verified altimeter setting 29.63." At 2214:31, the pilot advised he was going around and reported instrument flags. Subsequently the pilot requested to return to Great Falls.

Review of the approach plate for the ILS RWY 10L approach revealed that the minimum altitude to be maintained until reaching Saige is 5,700 feet msl. The decision height for a straight in landing on runway 10L is 3,784 feet msl. The required visibility to execute the approach is 2400 RVR or 1/4 mile. The reported weather conditions at Billings at 2156 were ceiling indefinite 100 feet agl, visibility 1/4 mile, altimeter setting 29.60, wind from 010 at 8 knots, temperature and dewpoint 1 degree C.

According to a written statement provided by the pilot, after intercepting the localizer, he was told by the Billings tower controller he "had an altitude conflict, they were showing [him] 200 feet low." He asked them to repeat the altimeter setting and "it was exactly what [he] was showing." The pilot was again told he had an altitude conflict, "and this time [his] NAV flags showed on the HSI and no glide slope." He "immediately added power to go around." During the climb, the landing "gear would not retract and the hydraulic light came on." He recycled the gear and then attempted to lower it manually; however, he was unable to get a green light for the right main landing gear. He requested to return to Great Falls and upon arriving there executed an ILS approach to runway 03 "without any problems." During the landing roll, the right main gear collapsed.

Examination of the airplane by an FAA inspector revealed that the upper drag brace for the right main landing gear was torn away from the spar. Examination of the roof of a gun club building, located about 1.65 miles from the threshold of runway 10L and 607 feet left of centerline, revealed two impact marks spaced about 14 feet apart, a distance corresponding to the main gear width of a Beech 99A. Part of the metal roofing and wooden support beams were dislodged by the impact. Additionally, landing gear drag brace pieces identified as coming from a Beech 99A were found about 80 yards from the building. The elevation of the building roof was estimated by FAA inspectors to be about 3,750 feet msl.

On October 20, 2004, the FAA conducted a flight inspection of the ILS RWY 10L approach to Billings and found the facility operation to be satisfactory. On October 21, 2004, under the supervision of an FAA inspector, the navigational radios in the accident airplane were tested. The VOR, glideslope, and localizer for the number 1 navigation/communication radio (a King KX165) were all found to be within operating limits. The glideslope and localizer for the number 2 navigation/communication radio (a King KX165) were also found to be within operating limits. The VOR bearing on the number 2 radio was out of limits. Additionally, the two ADFs, the two marker beacon receivers, the two HSIs, and the pilot's encoding altimeter were tested with no anomalies found.

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