JACKSONVILLE, IL, USA
N8640A
BEECH A35
THE PILOT REPORTED THAT HIS EN ROUTE ALTITUDE WAS 4,500 FT MSL, AND THAT HE ENCOUNTERED NO TURBULENCE. HE BEGAN A 150-155 MPH DESCENT BY REDUCING POWER TO 20 INCHES AND APPLYING LIGHT FORWARD PRESSURE TO THE YOKE. HE FELT A VIOLENT SHUDDER AND RELEASED THE PRESSURE ON THE YOKE, WHICH STOPPED THE SHUDDER. INSPECTION OF THE AIRPLANE REVEALED BUCKLED AND WRINKLED SKIN, POPPED RIVETS, AND BULKHEAD CRACKS. THE RUDDERVATORS HAD IMPROPER HARDWARE INSTALLED, A LOOSE BEARING, AND IMPROPERLY INSTALLED ELEVATOR TRIM TABS. THE RUDDERVATORS WERE TESTED FOR BALANCE. THE RIGHT RUDDERVATOR HAD A BALANCE OF 19.26 INCH-POUNDS AND THE LEFT RUDDERVATOR HAD A BALANCE OF 20.05 INCH-POUNDS. THE RIGHT RUDDERVATOR WAS WITHIN THE BALANCE LIMITS OF 16.8 TO 19.8 INCH-POUNDS, AND THE LEFT RUDDERVATOR WAS OUT OF BALANCE.
On June 4, 1995, at 1100 central daylight time, a Beech A35, N8640A, sustained substantial damage during descent near Jacksonville, Illinois. The private pilot reported no injury. The 14 CFR Part 91 flight departed Carbondale, Illinois, en route to Springfield, Illinois. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that he had climbed to 4500 feet en route to Jacksonville, Illinois, and encountered no turbulence. He had set the power settings at 22 inches of manifold pressure and 2200 RPM, which equated to 150-155 miles per hour airspeed. About 15 to 20 miles south of Jacksonville, he started his descent. He reported that he reduced the power to 20 inches of manifold pressure, and with his left hand he applied forward pressure to the yoke to set up a 400 to 500 foot per minute rate of descent. He reported that at that moment he felt and heard a very severe shudder in the tail. Startled, he released the forward pressure on the yoke, which immediately stopped the shudder. He reduced the power to 17 inches of manifold pressure and slowed the airplane to 125 miles per hour. After landing at Jacksonville Airport, he inspected the aircraft and discovered the damage to the tail. The aircraft was inspected by the airplane manufacturer's representative on June 7, 1995. A representative from the Federal Aviation Administration was present for a brief period prior to the inspection. The National Transportation Safety Board was notified of the aircraft accident on June 15, 1995. The results of the airplane manufacturer's inspection revealed that the empennage had sustained substantial damage. The aft fuselage skin exhibited signs of wrinkles and buckling, loose screws, and bulkhead cracks. Both stabilizer skins exhibited buckling on the top and bottom surfaces. Both ruddervators exhibited slight downward twisting of the outboard trailing edges, but neither ruddervator exhibited buckling. The inspection revealed that the left ruddervator inboard hinge support bearing had 0.010 radial and 1/32 inch axial wear. The inboard end of the left ruddervator could move about 1/32 inch perpendicular to its hinge line. An improper bolt was installed which was 1/32 inch too long. The trim tab hinge was misthreaded, and the trim tab could be moved 3/16 inch perpendicular to its hinge line. The right ruddervator exhibited negligible axial and radial wear. An improper bolt was installed which was 1/16 inch too long. The trim tab was misthreaded, and could move 3/16 inch perpendicular to its hinge line. The aircraft manufacturer's representative removed the ruddervators from the airplane and checked the balance of the ruddervators using the force balance method per the Bonanza 35 Series Shop Manual. He reported that both ruddervators exhibited a static underbalance moment of 18.54 inch pounds, which was within the required static balance range of 16.8 to 19.8 inch pounds. However, it was later determined that he had failed to attach the bolts and associated hardware on the pitch change horns on the ruddervator trim tabs, which resulted in an inaccurate measurement. (See attachments) On June 15, 1995, an Airworthiness Inspector from the Federal Aviation Administration examined the aircraft. He reported that the empennage had sustained substantial damage. The damage included buckled and wrinkled skin, popped rivets, and bulkhead cracks. (See attachment) The airplane's pitot/static system was checked to determine if the airspeed indicator was reliable. The test revealed that the system had excessive leakage. (See attachment) The airspeed indicator was removed and tested. The test revealed that airspeeds of 140 and 160 miles per hour were indicating higher airspeeds of 147 and 164 miles per hour, respectively. (See attachment) Examinations of the aircraft logbooks and maintenance work orders revealed that the ruddervators had been reskinned with factory new skins by a firm in Oklahoma on November 29, 1990, but had not been rebalanced. The ruddervators were balanced on January 22, 1991, by a firm in Illinois. The left ruddervator had a balance of 19.62 inch pounds, and the right ruddervator had a balance of 18.99 inch pounds. The aircraft control system rigging and cable tension were set on February 7, 1994, by a third firm located in St. Louis, Missouri. (See attachments) An annual inspection of the aircraft had been signed off on about March 4, 1994. The records show that all applicable Airworthiness Directives (AD) had been complied with, including AD 87-20-02R. (See attachments) The aircraft was purchased by the owner/pilot in August of 1994. A preinspection was performed by an Airframe and Powerplant (A&P) mechanic. On May 1, 1995, the same A&P mechanic performed an annual inspection of the aircraft. He noted in the logbook that AD 94-02-04, which superseded AD 87-20-02R, had been complied with. (See attachments) The ruddervators were delivered to the National Transportation Safety Board for inspection. The inspection revealed that the trim tabs on the ruddervators were misthreaded. The Beechcraft Bonanza 35 Series Shop Manual diagram of the trim tab shows how to install the trim tab the "right" way and the "wrong" way. The trim tabs had been installed the "wrong" way. The ruddervators had been reskinned in November of 1990 and since that time at least five A&P mechanics had not discovered the discrepancy. (See attachment) A series of tests were performed on the ruddervators to check for balance using the Actual Force Measurement method specified by the Beechcraft Bonanza 35 Series Shop Manual. It was determined that the right ruddervator had a balance of 19.26 inch pounds, and the left ruddervator had a balance of 20.05 inch pounds. The tests determined that the right ruddervator was within the balance limits of 16.8 to 19.8 inch pounds, and the left ruddervator was out of balance. (See attachment)
improper maintenance and inspection of the airplane's ruddervators.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
