JACKSON, MS, USA
N35WK
Beech F35
The pilot stated that he reduced the manifold pressure to 16 inches, and trimmed the airplane for a 650 feet per minute rate of descent, which increased the airspeed to about 155-160 mph indicated airspeed. He said the aircraft was stabilized at that speed, and he never exceeded that airspeed at anytime. He said the flight was in smooth air also, and all of a sudden, the ruddervators and whole tail started to "flutter" without any advance warning. He said he heard a "woofing" noise at perhaps a 1.5 to 2.0 hertz frequency, but further stated that not much shaking could be felt. He said he then reduced manifold pressure to idle, lowered the gear, trying to minimize control movements on the tail. After the speed was reduced, the pilot said that the "flutter" stopped. He said the total time the "flutter" occurred was about 5 seconds. He said at that time, he had nearly leveled the aircraft, and the speed had stabilized at 120 mph. According to the pilot, after an otherwise uneventful landing, he parked the aircraft and conducted a walk-around inspection, noting that there was extensive damage in the area of the aft empennage. The aircraft was examined and repaired by Trim-Aire Inc., Mexia, Texas, and the technician at Trim-Aire found that the empennage flight controls were out of rigging limits.
HISTORY OF FLIGHT On May 7, 2000, about 1700 central daylight time, a Beech F35, N35WK, registered to and operated by a private owner as a Title 14 CFR Part 91 personal flight, incurred substantial damage during descent to Jackson, Mississippi. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The private-rated pilot was not injured. The flight originated in Malden, Missouri, the same day, about 1440. The pilot stated that he had received vectors for the ILS runway 16L approach at Jackson, and was descending to 4,000 feet. The pilot further stated that the entire cruise had been done at 2,100 rpms, 21 inches of manifold pressure, and the airspeed was 135 mph indicated. The pilot said that after he was cleared to descend he reduced the manifold pressure to 16 inches, and trimmed the airplane for a 650 feet-per-minute rate of descent, which increased the airspeed to about 155-160 mph indicated airspeed. He said he stabilized the aircraft at that speed, and never exceeded that airspeed at anytime. According to the pilot, the flight was in smooth air, and the ruddervators and whole tail started to "flutter" without any advance warning. He said he heard a "woofing" noise at perhaps a 1.5 to 2.0 hertz frequency, but not much shaking could be felt. He said he then reduced manifold pressure to idle, lowered the gear, and tried not to introduce any control movements on the tail. After the speed was reduced, the pilot said that the "flutter" stopped, and the total time the "flutter" occurred was about 5 seconds. He said he had nearly leveled the aircraft, and the speed had stabilized at 120 mph. According to the pilot, at that time, the aircraft was normal to fly and trim, and although he was a bit shaken, he felt he had complete control again. He said he then continued the ILS approach, intercepting the localizer, followed by a normal landing and taxi to the fixed-based operator (FBO). After arriving at the FBO, the pilot said he conducted a walk-around inspection, and noted that there was extensive damage in the area of the empennage. The skin had wrinkled, paint had chipped, rivets had sheared, and stringers had buckled. PERSONNEL INFORMATION The pilot held an FAA private pilot certificate, with airplane single engine land and instrument ratings. The pilot also held an FAA second-class medical certificate, issued on July 28, 2000, which had the limitation, "must wear corrective lenses." The pilot had accumulated about 444 total flight hours, with about 88 flight hours in the same make and model as the accident airplane. AIRCRAFT INFORMATION The airplane is a 1955 model "v-tail" Beech 35 Bonanza, serial number D4366. The airframe total time was about 5,054 flight hours, and the recording tachometer showed about 1,012 hours at the time of the accident. The engine on the accident aircraft is a Continental E-225-8 engine, serial number 36026-D-4-8-R. The aircraft is equipped with a Hartzell HCA2V20-4A1 propeller, serial number AK391, under STC SAI-570, and had been overhauled at an airframe time of 4,953 flight hours. A detailed review of the aircraft's logbooks revealed the following: On July 31, 1973, a serviceable left aileron and a serviceable left elevator was installed. On November 16, 1973, the aircraft had been stripped, painted, and the elevator balanced. An entry on April 1, 1985, showed that the elevators were reinstalled but no reason was given. On July 27, 1987, Beech Kit 35-4016 -3 was installed in accordance with Beech Bulletin 2188. On June 17, 1988, AD-87-20-2 inspection was performed, and the aircraft and CG determined, along with the elevators being balanced. On August 3, 1991, the central elevator hinge on the right horizontal stabilizer was replaced, and the elevators were rigged. On March 14, 1997, the aircraft received an annual inspection, and the logbook annotated, "94-20-04 NA at this time." The airplane had received and annual inspection on June 5, 1999, at a total time of about 4802.6 flight hours, and October 29, 1999, the airplane was given a prepurchase inspection. As part of the prepurchase inspection, the logbook was annotated, "CW AD 94-20-04 Part (b) by inspection of fuselage bulkheads. Next inspection due at 5,073.0 hours total time." On October 7, 1999, the propeller was overhauled and shortly after, installed on the accident airplane. On October 24, the propeller was removed due to an oil transfer unit leak. The inner seal of the oil transfer unit was missing its rubber seal, and the rear-centering gasket, was also missing. The seals were replaced and the propeller reinstalled. METEOROLOGICAL INFORMATION Visual meteorological conditions prevailed at the time of the accident, and an instrument flight rules flight was filed. The Jackson International Airport 1654 surface weather observation was winds 210 degrees at 6 knots, gusting to 14 knots, visibility 10 statute miles, sky few clouds at 5,500 feet, temperature 84 degrees F, dew point temperature 66 degrees F, altimeter setting 29.99 inches Hg. The NTSB conducted a meteorological analysis of weather conditions along the N35WK's route of flight, and there was no evidence of any significant turbulence along the route of flight. For additional information, please see the Meteorological Factual Report,an attachment to this report. WRECKAGE AND IMPACT INFORMATION On May 10, 2000, the NTSB, the FAA and a representative from Raytheon Corporation examined the aircraft, and the examination revealed the following damage: On the left side, the aft left side fuselage, there was a diagonal crease from the top corner of FS233.5 and it proceeded at a 45-degree angle to the upper left corner of the access panel. The crease continued through the bottom center of the access panel to 6 inches forward of FS256.9 lower edge. Buckling had also occurred in the shape of a chevron, beginning at the bottom center of the access panel, and traveling aft to FS256.9, 3 inches forward and 1 inch up, back directly below the point of origination. There was also compression damage, 2 inches forward of FS272.0, 2 inches up from the bottom. The tail cone exhibited compression damage 5 inches below the cutout, and continued aft for 2 inches. There were also impact marks on the left leading edge of the cone that coincided with the location of fasteners. The bottom of the tail cone had some paint missing, and there was buckling between the rivets in a fore an aft direction. The rivet line in the tail cone area of the fuselage was elongated in an upward and aft direction, at an angle of about 45 degrees. On the right side there were two diagonal creases that started at the top of the fuselage, about 5 inches forward of FS246.3 and that traveled aft to both the right and left corners where the main spar of the stabilizer mated with the empennage. There was also a diagonal crease, which started at the upper corner of FS233.5, and continued down to the bottom of FS256.9. There were also diagonal creases that started at the rivet lines and proceeded aft to a point at FS256.9. The skin had pulled from FS256.9 in the following areas: At the first rivet line, four rivets had been pulled to the left. At the second rivet line seven rivets had pulled to the left. At the third rivet line, nine rivets had pulled to the right, and at the fourth rivet line, four rivets had pulled to the right. In addition, the lower skin between FS246.3 and FS256.9 was missing paint, and had displayed multiple creases. TESTS AND RESEARCH During the initial examination of the accident airplane, a pitot-static test was performed on the airplane. The results of the pitot-static test indicated that there was a static leak in the system somewhere in the vicinity of the left sidewall of the cabin. The static line was intact from the rear fuselage ports up to the rear baggage compartment, and the pitot-static lines to the airspeed, altimeter, and vertical speed indicator were also all intact. On May 11, 2000, a ruddervator balance check was performed, and the right ruddervator was 19.95 in-lbs static under balanced. The ruddervator weighed 8.28 lbs, and the counterweight weighed 2.97 lbs. The left ruddervator was 21.125 in. lbs static under balanced, with the ruddervator weighing 7.85 lbs, and the counterweight weighing 2.59 lbs. On June 2, 2000, an engine/propeller vibration analysis was performed, using a TEC Aviation Division Model 1000 vibration analyzer. Based on the manufacturer's guidelines, the mechanic recorded vibration values, averaging 1.15 Inches Per Second {IPS} Peak Amplitude, which are characterized as, "very rough ... a propeller balance is recommended." The vibration analysis had been performed with the spinner installed, and according to the mechanic, one of the engine's cylinders was soft at the time the propeller vibration analysis was done. The FAA's National Track Analysis Program (NTAP) of recorded radar data that contains position and altitude information, in 10- and 12-second intervals, showed that accident aircraft's airspeed to be about 120 knots, +/- 8 knots at 8,000 feet. NTAP data was not available during the descent, and approach to land phases of the flight. After the accident, the wings were removed and the aircraft was transported to Trim-Aire Aviation Inc, Mexia, Texas, for detailed examination and repair. The technician at Trim-Aire stated that he found that the empennage flight controls were out of rigging limits. In particular, the technician stated that after consulting the Beech 35 shop manual, he found that the travel stops, which should have been set to 35 degrees +/-2 degrees up, and 30 degrees +/- 2 degrees down, had been set instead to an average of 5 degrees. In addition, the technician stated that he found it impossible to install the differential jig assembly due to the adjacent bulkhead, and the right arm being about 2 inches ahead of the left. According to the technician, the lower elevator cable between the reduction bell crank and the elevator control arm was 23.62 inches, with several threads showing at the turnbuckle, instead of the Beech 35 shop manual's stated requirement that no threads on turnbuckle be visible. Furthermore, the technician said he found that the right side of the differential mechanism assembly had been erroneously positioned, and was being offset by lengthening the right aft push pull rod.
improper rigging of the rudder/elevators and differential mechanism assembly by unknown person(s), which resulting in what the pilot describes as inflight flutter of the tail section, which resulted in damage to the aft empennage area.
Source: NTSB Aviation Accident Database
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