WPR16FA102

The flight instructor was asked to complete a maintenance test flight of the airplane following the installation of a repaired carburetor. He elected to use the flight to provide instruction to the private pilot who had requested a checkout in the airplane. The private pilot reported that the flight was initially normal, but then the engine stopped responding to throttle control. According to the private pilot, the engine remained at idle power as the airplane descended and impacted trees in a residential area. Examination of the wreckage revealed that the carburetor throttle cable was detached from the throttle body linkage. The bolt and castellated nut used to secure the throttle cable to the linkage were found lying separately in the engine cowling; there was no evidence that a cotter pin had been used to secure the nut on the bolt, as required. It is likely that the loss of engine power resulted from the failure of the mechanic who installed the carburetor to install the cotter pin when he attached the throttle cable to the carburetor. During the maintenance test flight, the castellated nut backed off of the bolt, which resulted in a loss of throttle control.

The four-seat, single-engine, low-wing, retractable landing gear airplane, serial number D4599, was manufactured in 1956. It was powered by a Continental Motors E-225-8 engine, serial number 40062D, rated at 225 horsepower. The airplane was equipped with a Hartzell two- bladed adjustable-pitch propeller. A review of maintenance records showed that the most recent annual inspection was completed February 5, 2016, at a total airplane time of 5,968.69 hours. At the time of the annual inspection, the engine had accumulated a total of 1,677.47 hours since its most recent major overhaul. According to the airplane's maintenance records, the most recent maintenance was done on April 21, 2016, at a tachometer time of 1,520.9 hours. The tachometer time at the time of the accident was 1,521.31. The entry in the logbook for this maintenance stated: "Removed and Re-installed carburetor after repair, see 8130. All work done referencing Continental E225 maintenance manual." The entry was signed off by an airframe and powerplant (A&P) mechanic. In an interview conducted by the National Transportation Safety Board investigator-in-charge, the A&P mechanic who installed the carburetor stated that the person who had removed the carburetor left all of the hardware "really nicely," which made the installation easier. He added that he performed the installation by following the instructions in the engine maintenance manual. According to a fuel receipt, the airplane was fueled with about 30 gallons of 100LL aviation fuel at 1602 on the day of the accident. On May 07, 2016, about 1655 mountain standard time, a Beechcraft G35 Bonanza airplane, N4401D, sustained substantial damage during a forced landing following a loss of engine power near Surprise, Arizona. The flight instructor was fatally injured, and the private pilot receiving instruction was seriously injured. The airplane was registered to a private individual and was being operated by the flight instructor under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed. The maintenance test/instructional flight departed Glendale Municipal Airport (GEU), Glendale, Arizona, about 1630. According to a statement provided by a Federal Aviation Administration (FAA) inspector who interviewed the pilot, the purpose of the flight was an instructional check flight. The pilot reported that an "engine confidence check" was performed before departure, and no anomalies were noted. The flight then took off, completed one circuit in the traffic pattern. Radar data indicated that they then departed to the northeast. The pilot further reported that the flight was normal until they "experienced no response from the throttle control." The pilots followed the checklist, but the engine remained at idle. They were attempting to land at the auxiliary field but realized they were not going to make it and elected to turn "to brush off some speed (byhitting about 25-ft to 40-ft trees), before smashing into a very large pine tree." Radar data indicated that, about 10 miles north of GEU, about 3,725 ft, the airplane began a descent and made a 180° right turn followed by a 270° left turn and continued to descend, before making another 180° turn to the right. The last radar return was located about 0.15 mile southeast of the accident site, about 1,450 ft. A witness who observed the airplane descending over a parking lot stated that the airplane appeared low, slow, and quiet. The airplane then disappeared behind a building and subsequently impacted trees in a residential area. Multiple residents close to the accident site heard the impact and alerted first responders. The Maricopa County Coroner, Phoenix, Arizona, conducted an autopsy on the flight instructor. The medical examiner determined that the cause of death was "multiple blunt force injuries." The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicology tests on the flight instructor. According to the report, the following drugs were detected: unspecified amounts of citalopram in liver, 1.995 (ug/ml, ug/g) ketamine in liver, 1.446 (ug/ml, ug/g) ketamine in blood, unspecified amounts of midazolam in liver and blood, 1.618 (ug/ml, ug/g) norketamine in liver, and 0.405 (ug/ml, ug/g) norketamine in blood. Review of medical records indicated that midazolam and ketamine had been administered to the flight instructor as part of resuscitation attempts following the accident. Citalopram is an antidepressant medication available by prescription. While it is not generally considered impairing, the underlying depression can be cognitively impairing. At 1658, the weather reporting facility at Luke Air Force Base (LUF), located about 5 miles south of the accident site, reported wind 340° at 5 knots, 10 miles visibility, few clouds at 12,000 ft above ground level, temperature 25°C, dew point 5°C, and an altimeter setting of 29.82 inches of mercury. Flight Instructor The flight instructor, age 31, held a commercial pilot and a flight instructor certificate, both with airplane single-engine land and airplane multi-engine land ratings. He held a first-class airman medical certificate, issued on January 26, 2016, with the limitation of "not valid for any class after July 31, 2016." At the time of his last medical examination, the flight instructor reported 900 hours total flight experience of which 25 hours were in the last 6 months. Pilot Receiving Instruction The pilot receiving instruction, age 32, held a private pilot certificate with an airplane single-engine land rating. He held a first-class airman medical certificate issued on October 28, 2014, with no limitations. At the time of the medical examination, the pilot reported 11 hours total flight experience. On December 14, 2016, the carburetor was further examined and partially disassembled by NTSB investigators before being bench tested. The carburetorexhibited some impact damage to the mixture control arm. The bottom of the carburetor scoop displayed evidence of impact damage. The mixture and throttle controls moved freely from stop to stop. The fuel inlet screen and fuel strainer assembly were free of debris. The bench test indicated that the flow rates on 9 of the 11 test points were about 3 pounds per hour lower than the lower limit specified in the test parameters. According to the manufacturer, the low readings would have had minimal impact on the engine's ability to produce power. The initial impact point (IIP) was identified by several broken tree branches partially attached to a eucalyptus tree about 30 ft above ground level. The next point of impact was a large pine tree about 100 ft on about a 242° magnetic heading from the eucalyptus tree. The fuselage came to rest inverted about 30 ft from the pine tree, and the wings and empennage separated from the fuselage. All the major components of the airplane were accounted for at the accident site. During the on-scene examination, the carburetor throttle cable was found detached from the throttle body linkage. The bolt and castellated nut used to secure the throttle cable to the throttle body were found lying separately in the engine cowling; there was no evidence of the presence of a cotter pin, which should have been used to secure the nut on the bolt. Initial examination of the bolt and nut did not show any evidence of stripping of the threads, and neither the bolt nor nut was fractured.