# NTSB CHI96LA235: Beech B35, N5001C, Chesterfield, MO, June 24, 1996 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 23, 1996, 21:30 local (Jun 24, 1996, 02:30 UTC) - Place: Chesterfield, MO - Coordinates: 38.649223, -90.580619 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=38.6492&lon=-90.5806&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report July 28, 1997 - Report: Approved by Office Director - NTSB case key (mKey): 10306 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI96LA235 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/10306/pdf - Page: https://openairdocs.org/ntsb/CHI96LA235 ## Probable cause improperly balanced ruddervators and improperly installed ruddervator (elevator) trim tabs, due to improper maintenance, which resulted in ruddervator flutter and substantial damage in the area of the aft fuselage. Factors relating to the accident were: improper planning/decision by the owner/operator (pilot) by failing to ensure that the annual inspection and required aircraft maintenance were performed; and turbulence that led to vibration of the improperly balanced ruddervator. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - maintenance,annual inspection - not complied with, company/operator management (contributing factor) - maintenance - improper, other maintenance personnel (cause) - flight control,ruddervator - out of balance (cause) - flight control,elevator tab - improper (cause) - planning/decision - improper, pilot in command (contributing factor) - weather condition - turbulence (contributing factor) - flight control,ruddervator - flutter (cause) ## Analysis The pilot/owner reported that he was flying at 140 mph when he encountered light turbulence, and the airplane started to shake. The shaking lasted for about three seconds before the pilot/owner could reduce power and pull back on the yoke to slow the airplane. He then continued on to his destination where he made a normal landing. After landing, extensive damage was found in the area of the aft fuselage. An investigation revealed the airplane did not have a current annual inspection. There were pinholes in the pitot tube where it had been welded. The airspeed indicator was tested, and it did not meet specifications. The ruddervators were examined for proper balance and rigging. The service balance range for the ruddervators is 16.8 to 19.8 inch-pounds trailing edge heavy (underbalance). Using the counterbalance method, the underbalance of the left and right ruddervators was determined to be 22.53 and 22.68 inch-pounds, respectively. Both the left and right ruddervator trim tab hinge pins had been installed incorrectly. The incorrectly installed trim tabs exhibited significant vertical free play near the inboard end; the tabs also had restricted up and down angular travel. The ruddervator balance and the trim tab installation had been performed by two different aircraft maintenance facilities. ## Factual narrative On June 23, 1996, at 2130 central daylight time, a Beech B-35, N5001C, sustained substantial damage when it encountered moderate turbulence during cruise near Chesterfield, Missouri. After landing, the pilot inspected the airplane and discovered structural damage to the fuselage and stabilators. The private pilot reported no injuries himself or to the one passenger. The 14 CFR Part 91 flight departed Jefferson City, Missouri, en route to Chesterfield, Missouri. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that he was flying at 2,500 feet mean sea level (MSL) at 140 MPH. He reported encountering light turbulence and that the airplane started to shake. The shaking lasted for about three seconds before he could reduce the power and pull back on the yoke. He slowed the aircraft and was able to continue on to his destination where he made a normal landing. In a separate statement to the Federal Aviation Administration (FAA), the pilot indicated that the airspeed may have been higher than what was initially reported. The pilot reported to the FAA that the airspeed was 5 to 10 knots over the Red Line of 125 knots that was marked on the airspeed indicator. An examination of the aircraft and logbooks by an Airworthiness Inspector of the FAA revealed that the aircraft did not have a current annual inspection. An inspection of the pitot tube revealed that there were pinholes in the tube where it had been welded. The airspeed indicator was tested and it was determined that it did not meet specifications. Maintenance records and invoices indicated that the aircraft was extensively refurbished between November 1994 and May 1995. An invoice dated March 9, 1995, indicated that the trim tabs were installed on the ruddervators and were rigged and balanced. The annual inspection was signed on May 20, 1995. Included in the annual inspection sign-off was the statement, "Installed overhaul + balanced ruddervators." The aircraft logbook indicated that the aircraft was painted on August 16, 1995. The logbook entry reads: "...Ailerons, flaps, and ruddervators were removed. Repainted and reinstalled I.A.W. Manufacturers Specifications. The static balance check on the ailerons and ruddervators has been done. Aircraft approved for return to service." An inspection of the aircraft by the National Transportation Safety Board (NTSB) revealed extensive structural damage to the empennage of the airplane. The ruddervators were examined for proper balance and rigging. The service balance range for the ruddervators was 16.8 to 19.8 inch-pounds trailing edge heavy (underbalance). Using the counterbalance method, the underbalance of the left and right ruddervators was determined to be 22.53 and 22.68 inch-pounds, respectively. The lead counterweight in the left ruddervator balance horn weighed 1.94 pounds. Some of the lead had been removed by drilling and there were no mounting screws or washers installed. The lead counterweight for the right ruddervator weighed 2.17 pounds. Six lead washers of undetermined origin were attached and weighed 0.32 pounds. Both the left and right ruddervator trim tab hinge pins had been installed incorrectly. The left hinge pin was removed and reinstalled correctly for comparison purposes. The correctly installed tab exhibited no free play and could be rotated easily up and down. By comparison, the incorrectly installed right trim tab exhibited significant vertical free play near its inboard end and restricted up and down angular travel. (See Structural Factual Report) ## Aircraft - Registration: [N5001C](https://openairdocs.org/deregistered/N5001C-2015-05-27), registration cancelled 2015-05-27, S/N D-2263, built 1950 (OpenAirDocs) - Reported make and model: Beech B35 - Registry model: [Beech B35](https://openairdocs.org/model/beech-b35) (registry code 1151506) (OpenAirDocs) - Registry engine: [Continental E185 series](https://openairdocs.org/engine/continental-e185-series) (registry code 17014, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: D2263 - Airframe hours: 3620 - Engines: Continental E-225-8 225 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Kevin P. Cullinan - Airworthiness certificate: Standard, Normal - Last inspection: Annual, May 20, 1995, 84 hours before - Departed: JEF, JEFFERSON CITY, MO - Destination: SUS ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 36; private; airplane ratings: single-engine land; medical: class 3, valid medical--no waivers/lim.; seat: left; flight hours: 115 total, 31 in this make and model ## Weather - Conditions: Visual (VMC), Night/bright - Wind: 360° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 81 °F - Altimeter: 30.00 inHg ## Other investigations on N5001C (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB SEA67D0093](https://openairdocs.org/ntsb/SEA67D0093), Jul 28, 1966: Beech 35 (N5001C), Royal City, WA, substantial damage From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.