Kalispell, MT, USA
N1920E
Cessna 340A
While extending the landing gear the pilot heard a "loud bang" in the nose of the airplane. With both main landing gear having extended normally and the nose gear failing to extend, the pilot carried out the emergency landing gear checklist, but was unable to get the nose gear to extend. Air traffic control tower personnel subsequently confimred that the nose landing gear had not extended after the pilot did two flybys. The pilot then landed the airplane on both main landing gear, letting the aircraft settle onto its nose as airspeed bleed off, and it came to rest approximately 2,000 feet down the runway. A post-accident examination revealed that the adjusting bellcrank was fractured at the upper end where the fork bolt is normally inserted. The fracture features were consistent with overstress, and there was no evidence of any preexisting damage. The deformation and fractures appeared consistent with the bellcrank rotating relative to a stationary fork bolt during nose gear extension, such as could occur as a result of some obstruction or binding in the linkage forward of the bellcrank. The nature and cause of the binding in the linkages could not be determined.
On October 1, 2006, approximately 1800 mountain daylight time, a Cessna 340A, N1920E, sustained substantial damage following an emergency landing as a result of the airplane's nose landing gear failing to extend prior to landing at the Glacier Park International Airport (GPI), Kalispell, Montana. The left seat airline transport-rated student and the right seat commercial-rated flight instructor pilot were not injured. Visual meteorological conditions prevailed for the 14 CFR Part 91 instructional flight, and a flight plan was not filed. The local flight departed GPI about 1630. In a statement submitted to the NTSB investigator-in-charge (IIC), the pilot-rated student reported that after taking off, the landing gear retracted normally. The pilot-rated student stated that during the subsequent practice instrument approach the landing gear was extended during the initial configuration, and retracted again during the missed approach procedure; the extension and retraction were both normal. The pilot-rated student revealed that while configuring during the second practice instrument approach, and during the landing gear extension sequence, "We heard a loud bang in the nose of the aircraft. I looked at [the instructor] and then at the landing gear lights. We saw the main gear lights come on but no nose gear light, and the [nose] gear unsafe light remained on." The pilot-rated student and instructor then referred to the airplane's Pilot Operating Handbook, carried out the emergency landing gear checklist, but were unable to extend the nose gear to the down and locked position. After doing two flybys in close proximity to the Federal Aviation Administration control tower, tower personnel confirmed that both main landing gear were down, while the nose landing gear remained in the retracted position. After shutting both engines down on short final, the pilot-rated student landed the airplane on Runway 02. The airplane came to rest approximately 2,000 feet down the runway, resting on its nose and both main landing gear. The IIC retained the adjusting bellcrank from the nose landing gear retraction linkage, which was subsequently sent to the NTSB Materials Laboratory in Washington, D.C., for examination. An NTSB Senior Materials Engineer reported that the bellcrank was fractured at the upper end where the fork bolt is normally inserted, and that the fracture features were uniform light gray and rough, consistent with overstress fracture. The engineer stated that the upper piece of the bellcrank was also cracked and deformed, with the greatest crack opening distance located at the forward end of the bellcrank, with corresponding upward deformation at the upper side of the piece adjacent to the crack. The lower piece of the bellcrank contained portions of the forwardmost 6 threads for attaching the fork bolt, with thread peaks on the lower piece of the bellcrank deformed to the aft. (Refer to the Materials Laboratory Factual Report for a detailed description of the examination.)
The fracture of the adjusting bellcrank in overstress due to binding in a linkage forward of the bell crank.
Source: NTSB Aviation Accident Database
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