# NTSB FTW93IA242: Canadair CL-600-2B16, N392PT, San Antonio, TX, August 17, 1993 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: August 17, 1993, 09:45 local (14:45 UTC) - Place: San Antonio, TX - Coordinates: 29.539825, -98.489448 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=29.5398&lon=-98.4894&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 8 uninjured - Status: Completed, report August 17, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 18682 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW93IA242 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18682/pdf - Page: https://openairdocs.org/ntsb/FTW93IA242 ## Probable cause THE FRACTURE OF THE RUDDER QUADRANT DUE TO STRESS CORROSION. A FACTOR WAS THE MANUFACTURER'S IMPROPER SELECTION OF MATERIAL. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - normal - flight control,rudder - surge - flt control syst,rudder control - fractured (cause) - flt control syst,rudder control - stress corrosion (cause) - material inadequate,improper, manufacturer (contributing factor) - precautionary landing - initiated, pilot in command ## Analysis THE CREW EXPERIENCED AN UNCOMMANDED YAW TO THE RIGHT WHILE IN CRUISE FLIGHT AT FL410 WITH THE AUTO PILOT ENGAGED. A NORMAL LANDING WAS MADE WITHOUT INCIDENT AT THE INTENDED DESTINATION. EXAMINATION OF THE AIRPLANE'S RUDDER CONTROL REVEALED THAT THE SHAFT PORTION OF THE RUDDER QUADRANT WAS FRACTURED. METALLURGICAL EVALUATION OF THE FRACTURED SURFACE REVEALED THAT THE SEPARATION OF THE SHAFT PORTION WAS THE RESULT OF STRESS CORROSION CRACKING THAT INITIATED FROM OPPOSITE SIDES OF THE SHAFT AND PROGRESSED INWARD UNTIL ABOUT 60% OF THE SHAFT CROSS SECTION CRACKED DUE TO POOR CHOICE OF MATERIAL, IMPROPER RADIUS, AND EXCESSIVE TORQUE ON THE SHAFT NUT. ## Factual narrative On August 17, 1993, at 0945 central daylight time, a Canadair CL-600-2B16, N392PT, experienced an uncommanded yaw while in cruise flight at FL410, near San Antonio, Texas. There were no injuries to the two airline transport rated pilots and their six passengers. Visual meteorological conditions prevailed for the executive flight. According to the captain, the airplane was in cruise flight at the assigned altitude of FL410 in VMC conditions, with the auto pilot engaged, when the crew noticed an uncommanded yaw to the right without any warning or indication in the cockpit. A normal descent was initiated as the airspeed was reduced to 250 knots. After switching to a secondary flight guidance computer and disconnecting the yaw damper and the auto pilot, the pilots discovered that rudder deflections to the right were not possible. They continued to the San Antonio International Airport and landed without incident. Examination of the airplane's rudder control system by a Federal Aviation Administration inspector and a manufacturer's representative revealed that the shaft portion of the rudder quadrant was fractured. Metallurgical evaluation of the fracture surface and associated hardware revealed that the separation of the shaft portion was the result of stress corrosion cracking. The cracking initiated from the opposite sides of the shaft and progressed inward until about 60% of the shaft cross section was cracked. The Metallurgist's Factual Report is an enclosure. ## Aircraft - Registration: N392PT (not matched to a registry record) - Reported make and model: CANADAIR CL-600-2B16 (CL-600-2B1) - Category: Airplane - Serial number: 5110 - Airframe hours: 434 - Engines: GE CF34-3A 9250 lbs thrust turbo fan - Damage: No damage - Flight: Executive/Corporate, Part 91 - Registered owner: Pet Incorporated - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, May 9, 1993, 120 hours before - Departed: ALN, ALTON, MO - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 47; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 7,000 total, 1,800 in this make and model, 75 in the last 90 days, 30 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 82 °F ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19930817033479I](https://openairdocs.org/incident/19930817033479I), Aug 17, 1993: Cndair CL6002B16, Shreveport, LA. Flight control problem en route. Retrimmed. Continued. Right rudder control cable quadrant broke. 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.