Williams, CA, USA
N9952
TRAVEL AIR C 4000
A witness reported that during takeoff, the airplane reached about 8 ft above ground level, then suddenly pitched down and descended to ground contact. Postaccident examination of the airplane revealed a fractured and separated elevator control tube. A viscous liquid was inside the fractured tubing. A mixture analysis found signatures for emulsifiers, surfactants, and amines, which are often found in combination in corrosion-inhibiting compounds. The tubing fracture surfaces had features consistent with torsional overstress. A cross-section of the tube away from the fracture was examined. Corrosion was observed on the inner surfaces of the control tube, as well as significant thinning of the control tube wall thickness, which was 1/2 to 2/3 of the thickness of the least-corroded sections. The thinner wall thickness resulting from the corrosion likely could not support the same loading conditions as the full wall thickness, and likely led to the overstress separation of the control tube.
HISTORY OF FLIGHTOn August 30, 2014, about 1221 Pacific daylight time, a Travel Air C-4000, N9952, collided with terrain during the takeoff initial climb from the Williams Gliderport, Williams, California. The owner was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The commercial pilot sustained serious injuries. The airplane sustained substantial damage to the wings and fuselage. The local personal flight was departing. Visual meteorological conditions (VMC) prevailed, and no flight plan had been filed. Witnesses stated that the airplane reached about 8 feet above ground level (agl), and suddenly went nose first into the ground. An examination by a National Transportation Safety Board (NTSB) investigator revealed a fractured and separated control tube for the elevator. The investigator observed a viscous liquid inside the tubing. The tubing was removed for further examination. ADDITIONAL INFORMATIONThe pilot did not submit the National Transportation Safety Board Pilot/Operator Aircraft Accident/ Incident Form 6120.1. TESTS AND RESEARCHThe tubing was examined by the NTSB Material's Laboratory, and specialists performing exams on the viscous liquid and the tubing itself wrote factual reports, which are in the public docket for this accident. The viscous liquid inside the tubing had hardened into a glossy, gray-beige polymeric solid by the time it reached the laboratory. A sample of it was examined by a Fourier Transform Infrared (FTIR) spectrometer. Spectral peaks corresponded to a nitrogen-hydrogen bond, a carbon-hydrogen stretching bond, a carbon-oxygen double bond (carbonyl), a nitrogen-hydrogen bending bond, and a carbon-hydrogen bending bond. The spectrum suggested that the material contained an amine and a carboxylic acid. A spectrum library search did not identify a match for a single material. A mixture analysis search found signatures for emulsifiers, surfactants, and amines. The combination of these materials are often found in corrosion inhibiting compounds. The tubing fracture surfaces were heavily smeared, and the majority were covered with the same glossy, hard substance that coated the inside of the control tube. The areas of the fracture surfaces minimally covered by the hardened substance were minimally damaged, and had features consistent with overstress. The fracture occurred in a spiral along an approximately 45-degree angle, which was consistent with torsional overstress. A cross-section of the tube away from the fracture was examined. Corrosion was observed on the inner surfaces of the control tube, as well as significant thinning of the control tube wall thickness, which was 1/2 to 2/3 of the wall thickness of the least corroded sections.
The failure of the elevator control tube due to corrosion, which resulted in a loss of elevator control and collision with terrain.
Source: NTSB Aviation Accident Database
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