MITSUBISHI MU-2B-35, HILTON HEAD, S.C., AUG. 1, 2001–The NTSB determined the probable cause of this accident was improper maintenance/installation and inadequate inspection of the airplane’s flap torque tube joints, which resulted in the right flap torque tube assembly coupler becoming detached and the flaps developing asymmetrical lift when extended, resulting in an uncontrolled roll, a descent and impact with a tree during approach to land.
At about 7:51 a.m. MU-2 N1VY, registered to MU-2 LLC and operated by Bankair as a Part 91 positioning flight, crashed in Hilton Head. An IFR flight plan had been filed, though the aircraft was in VMC. The sole-occupant commercial pilot was killed and the aircraft was destroyed. The flight originated from Savannah, Ga., at about 7:41 a.m.
The pilot reported that he had the airport in sight and was given approval to make a frequency change and told to squawk 1200. At 7:50 a.m., the Savannah controller noticed on radar that the aircraft had initiated a gradual descent from 2,000 feet to 1,000 feet. At 7:51, the altitude increased to 1,300 feet and then the aircraft disappeared from the radar screen.
A witness at HXD who was monitoring Unicom reported that the pilot called for a traffic advisory. The witness replied that traffic was landing and departing from Runway 3, which the pilot acknowledged. Witnesses reported seeing the aircraft in a right-wing-down, nose-low attitude as it initially hit trees and then the grounds of a golf course. A fire ensued and the aircraft was destroyed.
The pilot held an FAA commercial certificate, a current second-class medical and an A&P license. Bankair records showed that after starting with the company as a mechanic he became a pilot. He had accumulated about 500 flight hours in type, and about 114 flight hours during the past 90 days, of which about 77 were in the MU-2.
Examination revealed that the aircraft’s left wing flap was extended to 40 degrees and the right to about 20 degrees. The right flap torque tube assembly between the flap motor and the flap-stop assembly had disconnected because a cotter pin had not been placed through the spline and the coupler consistent with normal installation according to Mitsubishi’s maintenance manual, or as specified in AD 88-23-01.
Instead, the cotter pin had missed the male spline on the flap motor. In addition, the flap coupler on the opposite side of the flap motor was found not to have a cotter pin installed.
Maintenance records showed that about 87 flight hours before the accident, the airplane was inspected per Airworthiness Directive 88-23-01, which required the disassembly, inspection and reassembly of the flap torque tube joints. On July 9, 2001, the airplane was given a phase 1 inspection, and Bankair records showed that the applicable maintenance items were performed, and the airplane returned to service.
The damage on both engines was consistent with their operating normally at the time of impact, and the propeller damage indicated that both were rotating with power applied at impact.
Toxicological tests were conducted for carbon monoxide, cyanide, volatiles and drugs, and the results for each were negative.