N159MC

On December 28, 1995, at 1748 central standard time (CST), a Fairchild SA227-AC, N159MC, operated by Mesaba Airlines, of Minneapolis, Minnesota, received no damage after the captain reported that the airplane had restricted elevator travel on landing at Bemidji County Airport, Bemidji, Minnesota. There were no injuries to the two crew members, or 14 passengers aboard the airplane. There was no emergency evacuation. The flight was a domestic passenger flight, operating under 14 CFR Part 135, from Minneapolis to Bemidji, Minnesota. Visual meteorological conditions prevailed at the time, and an IFR flight plan was filed.

According to the pilot's written statement, during a normal descent on short final (100 to 200 feet above ground) in landing configuration, the crew reported that the airplane pitched down excessively and the elevator could not be moved to the full up position. The crew initiated a go-around and used power to control pitch for landing. The landing was hard and flat. Sixteen flights before this incident, the tail section had maintenance conducted on it according to Mesaba's maintenance records.

The Federal Aviation Administration Principal Maintenance Inspector (PMI) stated that Mesaba records show maintenance performed on N159MC in the area of the elevator quadrant. During the maintenance, a mechanic following maintenance manual procedures, removed the upper elevator bolt and related hardware.

A mechanic who performed maintenance on the airplane stated that with the quadrant removed and on a bench, another mechanic loosely installed the hardware back on to the quadrant, so the hardware would not be lost. "Loosely installed" as stated by the mechanic refers to the bolt and related hardware installed, with the self locking nut tightened manually and not properly torqued. The self locking feature of the nut was deteriorated. The nut that was removed from N159MC could be run down on the bolt to a point where one thread extended beyond the nut. This position on the nut is close to the appearance of a nut installed with the proper torque. The FAA Inspector stated that in comparison to a new nut it could only be run down a few turns on the bolt. Mesaba's inspector did not notice the improper installation.

The post-maintenance investigation found a worked out upper elevator stop bolt in the elevator quadrant prevented elevator movement from about neutral to full up position. The bolt worked out about two inches. Upon movement of the control column to the full up position, the worked out bolt, moving upward with the elevator control quadrant, contacted the underside of a stringer (the first stringer just above the related access panel on the right side of the vertical stabilizer). This contact prevented further movement of the elevator in the up direction. The bolt appeared to be bent from this contact and force exerted by the crew when pulling the control column back.