Figure 2. Missing cotter pin and unsecured throttle lever locking nut.
The pilot of a Piper PA-28-140 airplane was practicing takeoffs and landings when the engine became unresponsive to throttle inputs, resulting in a forced landing onto a highway where the airplane was substantially damaged. Examination of the engine revealed that the carburetor throttle lever lock nut was only finger-tight, and its cotter pin was absent (see figure 2), which likely resulted in the throttle lever intermittently disengaging from the serrated throttle shaft when the pilot manipulated the throttle. Partial loss of engine power could have been avoided if the mechanic had properly secured the throttle lever lock nut and replaced the missing cotter pin. (WPR19LA065)
Figure 3. Separated throttle cable.
A Cessna U206F airplane lost partial engine power while returning to the airport during a commercial sightseeing flight. The pilots were unable to regain full engine power. As the pilots retarded the throttle to idle, the throttle and about 2 ft of the throttle control cable came out of the control panel. The airplane sustained substantial damage during the forced landing onto a dirt road. A review of the airplane’s maintenance logbooks revealed that the throttle cable had been installed more than 20 years before the accident; postaccident examination found that it had separated, as shown in figure 3. Although the airplane’s maintenance manual suggested replacing the engine controls (including the throttle cable) at every engine overhaul, the operator had not replaced the accident throttle cable during the previous engine overhaul, which was completed 163 flight hours before the accident.
This accident might have been avoided if the throttle cable had been replaced during the last engine overhaul. (WPR17LA144)
Figure 4. Incorrect installation of spring and hardware and broken mixture cable.
A Robinson R-22B helicopter experienced a total loss of engine power while being maneuvered about 3,000 ft above ground level. The pilot entered an autorotation, and the helicopter touched down on a road, struck an unoccupied automobile, and was substantially damaged. Examination of the helicopter revealed that the mixture cable had broken and separated from the mixture bellcrank control arm located on the carburetor. The bellcrank was positioned near the idle/cutoff position, and the spring was inserted in the wrong direction. During an airframe overhaul that was performed about 16 flight hours before the accident, a mechanic's apprentice improperly rigged the mixture-to-bellcrank hardware, which prevented the mixture cable from moving freely and caused it to break (see figure 4). Had the mechanic properly inspected the apprentice’s work, he likely would have discovered the improperly rigged mixture control assembly that led to total loss of engine power. (WPR13LA222)
