Okeechobee, FL, USA
N3315C
Beech E35
While climbing on course shortly after takeoff on a cross-country flight, the engine briefly ran roughly before losing partial power. The private pilot maneuvered the airplane and executed an off airport forced landing with the landing gear retracted. A postimpact fire on the right side of the airplane ensued after it came to rest, and the airplane was destroyed. Examination of the engine following accident revealed the throttle control cable was separated from the intact carburetor throttle control lever. Examination of a bolt with an attached washer, a separate washer, and a castellated nut found in the engine compartment revealed the nut was not self-locking and the tare torque was no greater than 0.2 pound-force-inch. There were no remains of a cotter pin in the recovered drilled bolt. Although the mixture control cable remained attached to the intact mixture control lever, a castellated nut and cotter pin were not attached to the bolt. Further examination of the engine and its systems otherwise revealed no evidence of preimpact mechanical failure or malfunction; Given this evidence, it is likely that the loss of engine power was due to the separation of the throttle control cable from the carburetor, which rendered sustained flight impossible. A review of the maintenance records indicated that more than 13 months before the accident, the pressure carburetor was overhauled then reinstalled. It was the subject of two scheduled inspections before the accident. The maintenance records did not document any subsequent work to the throttle or mixture control cables. The mechanic indicated that he was certain that the proper hardware to secure the throttle cable to the throttle control lever was installed at carburetor installation and during both subsequent scheduled inspections. Although the nut lacked any appreciable tare torque, it could not be determined when it separated or if the mechanic failed to install a cotter pin to secure the throttle cable to the throttle control lever more than 13 months and a minimum of 192 flight hours earlier. Although possible, it is unlikely that the mechanic would have twice overlooked the lack of proper securing hardware during the subsequent scheduled inspections.
HISTORY OF FLIGHTOn November 23, 2019, about 1244 eastern standard time, a Beech E35, N3315C, was destroyed when it was involved in an accident near Okeechobee, Florida. The pilot and two passengers sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that after starting the engine, he taxied to the active runway, where he allowed the engine oil temperature to come to normal operating temperature due to the short taxi. Once the oil temperature was normal, he did an engine run-up, which included a check of the magnetos; each magneto drop was about 75 rpm. He also checked the vacuum pump reading, instruments, and verified the flight controls moved in the proper direction and were free and clear. After takeoff he retracted the landing gear. The pilot had no recollection of events from shortly after takeoff until November 26. The passenger seated in the right front seat reported that everything seemed normal to him until the pilot began a right climbing turn. Within seconds after starting the turn, the engine ran rough and then lost power. He recalled the pilot attempting to try to restart the engine, levelling off, then maintaining a controlled descent straight ahead. The passenger did not notice what any engine instruments were reading nor did he see the stall warning light illuminate or hear the stall warning horn. There was no fire prior to impact with the ground, but there was a fire on the right side of the airplane when it came to rest. AIRCRAFT INFORMATIONThe airplane’s fuel metering system consisted of a pressure carburetor that was controlled from the cockpit by throttle and mixture controls. The throttle control assembly connected to the throttle lever at the pressure carburetor by a drilled bolt, castellated nut, cotter pin, and washers as necessary. Review of the maintenance records revealed on October 1, 2018, at a tachometer time of 1,318.8 hours, or 4,866.9 total engine hours, the pressure carburetor was overhauled, and re-installed. A 100-hour inspection of the engine was performed on March 23, 2019, at a tachometer time of 1,443.16 hours, or 4,991.26 total engine hours. The engine’s last annual/100-hour inspection was performed on October 1, 2019, at a tachometer time of 1,511.1 hours, or 5,059.2 total engine hours. The airplane had accrued about 192 hours at the last annual/100-hour inspection since the carburetor was installed. There were no other entries in the engine maintenance records documenting any work to the throttle or mixture control cables. The mechanic who signed off the installation of the carburetor and the subsequent two scheduled inspections stated that he was certain that during the carburetor installation and scheduled inspections, the proper hardware to secure the throttle cable would have been installed. AIRPORT INFORMATIONThe airplane’s fuel metering system consisted of a pressure carburetor that was controlled from the cockpit by throttle and mixture controls. The throttle control assembly connected to the throttle lever at the pressure carburetor by a drilled bolt, castellated nut, cotter pin, and washers as necessary. Review of the maintenance records revealed on October 1, 2018, at a tachometer time of 1,318.8 hours, or 4,866.9 total engine hours, the pressure carburetor was overhauled, and re-installed. A 100-hour inspection of the engine was performed on March 23, 2019, at a tachometer time of 1,443.16 hours, or 4,991.26 total engine hours. The engine’s last annual/100-hour inspection was performed on October 1, 2019, at a tachometer time of 1,511.1 hours, or 5,059.2 total engine hours. The airplane had accrued about 192 hours at the last annual/100-hour inspection since the carburetor was installed. There were no other entries in the engine maintenance records documenting any work to the throttle or mixture control cables. The mechanic who signed off the installation of the carburetor and the subsequent two scheduled inspections stated that he was certain that during the carburetor installation and scheduled inspections, the proper hardware to secure the throttle cable would have been installed. WRECKAGE AND IMPACT INFORMATIONExamination of the wreckage following recovery revealed the cockpit was nearly fully consumed by the postcrash fire. Examination of the flight controls for roll, pitch, and yaw revealed no evidence of preimpact failure or malfunction. Examination of the engine following recovery of the airplane revealed the throttle valve of the Bendix PS-5C carburetor was near idle, and the throttle control cable was detached from the intact carburetor throttle control lever. The mixture control cable remained attached to the mixture control lever by a drilled bolt; however, it did not have a castellated nut or cotter pin installed. Examination of the left side of the lower engine cowling revealed a bolt with attached washer, another larger washer, and a castellated nut. Further examination of the engine and its systems revealed no other evidence of preimpact failure or malfunction. The rod-end for the throttle cable, throttle control lever, and parts found in the lower engine cowling were examined by the National Transportation Safety Board (NTSB) Materials Laboratory, which found that the hole in the bolt shank did not contain any remnants of a cotter pin. The threads of the bolt and nut, which was not self-locking, were intact. Examination of the throttle control lever revealed circumferential grooves consistent with bolt thread contact on the interior surface. Spacing between adjacent grooves varied in the hole with wider spacing between grooves closer to the inboard side of the lever and narrower spacing closer to the outboard side. The spacing of the grooves with the narrower spacing had a finer pitch than the thread pitch of the recovered bolt. The grooves with the wider spacing appeared partially worn, consistent with contact with a smooth rod shape such as the grip of the bolt recovered from the cowling at the time of the accident. After examination of the parts was completed, a light oil was applied to the bolt threads, and the nut was threaded onto the bolt. The nut threaded easily by hand with little or no resistance. The tare torque of the nut tested no higher than 0.2 pound-force-inch.
The separation of the throttle control cable from the carburetor throttle control lever resulting in the near total loss of engine power. Contributing to the separation of the throttle cable was the lack of proper securing hardware by unknown maintenance personnel.
Source: NTSB Aviation Accident Database
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