# NTSB DEN08IA030: Beech C90A, N871KS, Emporia, KS, September 22, 2007 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: September 22, 2007, 00:15 local (05:15 UTC) - Place: Emporia, KS - Coordinates: 38.331943, -96.191108 - Nearby events: https://openairdocs.org/map.md?lat=38.3319&lon=-96.1911&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 8 uninjured - Status: Completed, report April 30, 2008 - Report: Approved by Office Director - Parties: Federal Aviation Administration - NTSB case key (mKey): 67096 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN08IA030 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/67096/pdf - Page: https://openairdocs.org/ntsb/DEN08IA030 ## Probable cause The improper installation of the right elevator trim tab attachment hardware by maintenance personnel which resulted in excessive wear, fatigue, and the failure of the push-pull tube. ## Analysis While in cruise flight at 12,000 feet mean sea level, the airplane suddenly began "shuddering with a severe high frequency vibration." The pilot stated that the "vibration was in the entire airframe, not specifically the flight controls, so I had no clue where it was coming from." The pilot reduced the power on the left engine; however, the vibration continued. The pilot reduced the power on the right engine, and the vibration stopped. The pilot then shutdown and secured the right engine. Within a couple minutes of securing the right engine, the vibration "returned just as bad as before." The pilot then elected to divert to a nearby airport. The pilot lowered the landing gear during the approach, and the vibration stopped again. The airplane landed uneventfully. During a post flight inspection, the pilot observed the right elevator trim tab push rod was broken. The clevis which connected to the trim tab surface was "pinched due to an overtorqued bolt and nut." Metallurgical examination of the broken rod revealed a fatigue crack that propagated through at least 95 percent of the thread cross section. Maintenance records revealed the right elevator trim tab push-pull tube bolts and bushings were removed and replaced. At the time of the incident, the airframe had accumulated 101.5 flight hours since the inspection, and no additional maintenance to the right elevator trim system was noted in the maintenance records. ## Factual narrative On September 22, 2007, approximately 0015 central daylight time, a Beech C90A twin-turboprop airplane, N871KS, experienced a failure of the right elevator trim-tab pushrod during cruise flight and the flight crew executed an emergency landing to Emporia, Kansas. The pilot, co-pilot, and 6 passengers were not injured. The airplane was registered to and operated by the Kansas State University, Salina, Kansas. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the Title 14 Code of Federal Regulations Part 91 business flight. The flight departed Tulsa, Oklahoma, and was destined for Manhattan, Kansas. According to the pilot, while in cruise flight at 12,000 feet mean sea level, the airplane suddenly began "shuddering with a severe high frequency vibration. The vibration was in the entire airframe, not specifically the flight controls, so I had no clue where it was coming from." The pilot reduced the power on the left engine, however, the vibration continued; the pilot reduced the power on the right engine, and the vibration stopped. The pilot then shutdown and secured the right engine. Within a couple minutes of securing the right engine, the vibration "returned just as bad as before." The pilot then elected to divert to Emporia. The pilot lowered the landing gear during the approach, and the vibration stopped again. Subsequently, the airplane landed uneventfully at Emporia. During a post flight inspection, the pilot observed the right elevator trim tab push rod was broken. According to a mechanic who removed the broken push rod, the clevis which connected to the trim tab surface was "pinched due to an overtorqued bolt and nut." Breakaway torque was not measured during the removal of the rod. The trim tab surface horn inner bushing was free to rotate within the outer bushing. The pilot, who regularly piloted the incident airplane, stated that he noted no abnormal operations with the trim system prior to the failure. On November 19, 2007, the NTSB materials laboratory in Washington, DC, examined the broken push rod. According to the metallurgist, the torque tube/linkage contained a rod end on each side of the fracture. One rod end fractured at the thread portion. Detailed bench binocular and scanning electron microscope examination of the fracture face from the rod end revealed a fatigue crack that propagated through at least 95 percent of the thread cross section. A review of the airframe maintenance records revealed that the airplane was maintained in accordance with a manufacturer's approved inspection program. On February 14, 2007, during a phase 3 and 4 inspection at a Raytheon service center, the right elevator trim tab push-pull tube bolts and bushings were removed and replaced. At the time of the incident, the airframe had accumulated 101.5 flight hours since the inspection, and no additional maintenance to the right elevator trim system was noted in the maintenance records. The following is an excerpt from the airframe maintenance manual elevator trim tab installation procedures: "Insure proper lubrication and install the bolt and nut, torque to 25-30 inch-pounds and install the cotter pin. The bolt, inner bushing, and clevis must be held tightly so they will rotate together when the trim tab is operated. The bolt must not turn in the inner bushing. Movement should be between the bushings." ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - maintenance,installation - improper, other maintenance personnel (cause) - flight control surfaces/attachments - overtorque (cause) - flt control syst,elevator control cable/rod - fatigue (cause) - flt control syst,elevator control cable/rod - failure (cause) - Loss of control - in flight, cruise ## Aircraft - Registration: [N871KS](https://openairdocs.org/deregistered/N871KS-2024-08-15), registration cancelled 2024-08-15, S/N LJ-1277, built 1991 (OpenAirDocs) - Reported make and model: Beech C90A - Registry model: [Beech C90A](https://openairdocs.org/model/beech-c90a) (registry code 1152911) (OpenAirDocs) - Registry engine: [Pratt & Whitney Canada PT6A-21](https://openairdocs.org/engine/pratt-whitney-canada-pt6a-21) (registry code 52172, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: LJ-1277 - Airframe hours: 3688 - Engines: Pratt & Whitney Canada PT6A-21 550 horsepower turbo prop - Damage: No damage - Flight: Business, Part 91 - Registered owner: Kansas State University - Airworthiness certificate: Standard, Normal - Last inspection: Continuous airworthiness, February 1, 2007, 101.5 hours before - Departed: TUL, TULSA, OK - Destination: MHK, MANHATTAN, KS - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 54; injuries: none; airline transport; airplane ratings: single-engine land, multi-engine land, single-engine sea; instrument ratings: airplane, helicopter; medical: class 2, without waivers/limitations; last flight review June 1, 2007; seat: left; flight hours: 9,546 total, 999 in this make and model, 8,494 as pilot in command, 65 in the last 90 days, 33 in the last 30 days, 7 in the last 24 hours - Co-pilot; age 22; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review December 1, 2006; seat: right; flight hours: 883 total, 8 in this make and model, 479 as pilot in command, 100 in the last 90 days, 8 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night - Visibility: 10 statute miles - Lowest ceiling: 8,000 ft broken 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.