History of Flight
On April 20, 2008, about 1330 eastern daylight time, a Beech G35, N4606D, sustained substantial damage following uncommanded pitch and roll oscillations in cruise flight near New Smyrna Beach, Florida. The certificated commercial pilot and the pilot-rated passenger were not injured. Visual meteorological conditions prevailed for the flight that originated at Henry County Airport (PHT), Paris, Tennessee, and was destined for Melbourne International Airport (MLB), Melbourne, Florida. No flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91.
In a written statement, the pilot described an uneventful flight until he requested his arrival descent from air traffic control. At that time, the airplane was level at 9,000 feet, at about 125 knots indicated airspeed, with the GPS showing 147 knots true airspeed. Prior to initiating the descent, the pilot "heard and felt 5-6 sharp vibrations with about a 2-3 hertz frequency. The aircraft pitched up and down violently a few degrees and rolled a few degrees to the left." The pilot-rated passenger reported hearing "popping and tearing" from the area of the baggage door.
The pilot disengaged the autopilot, slowed the airplane, and the vibrations stopped. He then performed a slow descent and completed a safe landing at Melbourne Regional Airport. After landing, the pilot noted that the g meter had recorded loads of +3.9 g's to -1 g. Typical loads during moderate turbulence encounters were "+0.5 g's to +2.0 g's."
Interpolation of radar data revealed level cruise airspeed above design maneuvering speed (VA-114 kts) and airspeeds above design cruising speed (VC-153 kts) during descent. There was no evidence of airspeeds above the airplane's never-exceed speed (VNE-176 kts).
A hand-held Global Positioning System (GPS) receiver was on board and in use. The GPS unit was requested from the pilot multiple times but was not submitted for examination.
Personnel Information
The pilot held an airline transport pilot certificate with ratings for airplane single-engine land and sea, multi-engine land, and instrument airplane. He also held a flight instructor certificate with ratings for airplane single-engine, multi-engine, and instrument airplane. His most recent FAA second-class medical certificate was issued on December 15, 2007. The pilot reported 8,200 total hours of flight experience, 3,500 hours in single-engine airplanes, and 120 hours in the Beech G35.
Aircraft Information
According to FAA and maintenance records, the airplane was manufactured in 1956 and had accrued 4,964 total aircraft hours. The most recent annual inspection was completed on May 4, 2007, at 4,937 total aircraft hours. The airplane was in compliance with Beech Service Bulletin 2188 (Tail Reinforcing Kit 35-4016-3S), which was installed on October 14, 1987.
Meteorological Information
At 1347, the weather reported at New Smyrna Municipal Airport (EVB) included scattered clouds at 10,000 feet, winds from 030 degrees at 6 knots, visibility 10 miles, temperature 19 degrees Celsius, and dew point 5 degrees Celsius. There were no weather advisories current over central Florida surrounding the period of the accident.
A weather study from a National Transportation Safety Board Senior Meteorologist revealed cumulus clouds developing in the area on satellite and WSR-88D imagery, indicating potential for convectively induced turbulence from towering cumulus clouds. Soundings noted an inversion near 9,500 feet with rapidly drying air above. Vertical wind shear was 5 knots per 1,000 feet at that layer, corresponding to moderate or greater turbulence. No weather advisories were current over central Florida.
Wreckage and Impact Information
Examination of the airplane, a monoplane with a "V" tail, by Hawker-Beechcraft representatives revealed rear fuselage skin and stringer buckling between flight station 233 and flight station 256 bulkheads. There was downward bending of the rear fuselage with diagonal buckling of the skin on each side and tearing of the skin on the bottom.
The two elevators were found properly attached and properly balanced. Control rigging could not be confirmed due to aircraft damage, but the cables were found "taught" using hand force. The propeller and the engine's dynamic shock mounts were in "good" condition. An FAA aviation safety inspector supervised the examination and concurred with the manufacturer's field notes.