Ontario, CA, USA
N9914M
Cessna 182
The airplane encountered severe turbulence and downdrafts after flying through a mountain pass, and the pilot applied full engine power in an effort to arrest the descent. The engine did not respond, and the pilot performed a forced landing onto a highway. While the pilot attempted to avoid automobiles, the airplane landed hard and sustained substantial damage. Examination revealed that about 20 years and 300 flight hours before the accident, threaded studs had been used to mount the carburetor airbox to the carburetor inlet, rather than the appropriate bolts. The studs had been overdriven and penetrated the carburetor bowl, fracturing the bowl housing. Fragments of the damaged housing lay at the bottom of the bowl until the accident flight, when the turbulence likely caused them to migrate and interfere with either the float or the fuel mixture metering system.
On November 8, 2018, at 1553 Pacific standard time, a Cessna 182P, N9914M, was substantially damaged when it was involved in an accident near Upland, California. The airline transport pilot, commercial pilot, and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The airplane was flying south through the Cajon Pass, and once clear of the pass at an altitude of 6,500 ft mean sea level (msl) the commercial pilot initiated a turn to the west. The airplane then encountered what the pilot presumed to be leeside turbulence from the mountain range, so she turned the airplane to the south to find smoother air; however, the turbulence became more severe, and the airplane began to rapidly descend. The airline transport pilot attempted to change the radio frequency to the Ontario Airport Control Tower, so he could advise controllers that the flight would need to transition through their airspace in order to escape the downdrafts. He was struggling to switch the radio’s frequency control due to the turbulence, but eventually was able to establish contact. By this time the airplane had descended to 2,000 ft msl (about 500 ft above ground level), and the airline transport pilot requested that the commercial pilot arrest the descent. The commercial pilot applied full engine power, but the engine did not respond. The airline transport pilot then took the flight controls, applied full rich fuel mixture and carburetor heat, and the engine momentarily regained power. Having reached about 2,300 ft msl, the engine again lost power, and the pilot decided to look for an area to land. With limited options, he decided to land on the westbound lanes of a freeway. He maneuvered over a set of trees, and just before touchdown, a vehicle appeared under the right wing. He attempted to avoid a collision, and while doing so, the airplane landed hard. The airplane sustained substantial damage to the forward fuselage. Postaccident examination revealed that both fuel tanks and the gascolator contained fuel; the fuel tank vent was unobstructed, and fuel flowed to the carburetor when the "BOTH" position of the fuel tank valve was selected. The engine mounts were bent, and the engine sustained damage limited to a crack in the inlet "Y" manifold, which appeared to have struck the firewall on impact. All fuel lines along with the throttle, mixture, carburetor heat, and propeller controls were intact. The bottom spark plug electrodes were coated in light grey deposits and exhibited normal wear signatures when compared to the Champion AV-27 Check-A-Plug chart. No anomalies were noted with the engine or airframe that would have precluded normal operation. The engine was removed from the airframe and configured in a test cell with a replacement "Y" manifold. After engine start, the engine reached its operating temperature, but would not accelerate beyond a speed of 1,200 rpm. The carburetor was replaced, and the engine then operated normally throughout its speed range. The accident carburetor was a Marvel-Schebler model MA-4-5. Maintenance logbooks indicated that it was rebuilt and installed when the engine was last overhauled in September 1998, 288.4 flight hours before the accident. No other maintenance was performed on the carburetor assembly beyond the replacement of the carburetor heat airbox hardware, 27.8 flight hours after the engine overhaul. The carburetor was disassembled and examined. Brass floats had been utilized and bore a date stamp of May 1997. The floats were intact and showed no evidence of leak. Examination revealed that four 1-inch-long studs had been used to mount the airbox assembly to the carburetor bowl, and the forward studs appeared to have penetrated about 1/8 inch into the carburetor bowl. (see Figure 1.) Three fragments of aluminum material ranging in size from 1/8 to 5/8 of an inch were found at the bottom of the bowl. (see Figure 2.) The material had a polished appearance and a shape that matched that of the bowl housing where the studs had broken through. Examination of the Cessna illustrated parts catalog applicable to the accident airplane revealed that the appropriate hardware for mounting the airbox to the carburetor was four MS20074-04-3, 0.4690-inch-long bolts, rather than the 1-inch studs used. (see Figure 3.) The carburetor was sent to the facilities of Marvel-Schebler for further examination under the oversight of an FAA inspector. During the examination, additional metallic particles were found within the fuel mixture metering sleeve, along with scratches and abrasions on the sides of the float. Figure 1 – Yellow Arrows Indicate Forward Studs Penetrating into the Bowl Housing, along with Housing Fragments Figure 2 – Bowl Housing Fragments Figure 3 – Studs in Bowl Housing
A partial loss of engine power during descent due to an incorrectly installed carburetor.
Source: NTSB Aviation Accident Database
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