Accident Overview
On November 8, 2018, at 1553 Pacific standard time, a Cessna 182P (registration N9914M) was substantially damaged during a forced landing on a freeway near Upland, California. The airplane was operating as a Title 14 Code of Federal Regulations Part 91 personal flight, with an airline transport pilot, a commercial pilot, and one passenger aboard. None of the occupants were injured.
Flight and Turbulence Encounter
The airplane was flying south through the Cajon Pass. After clearing the pass at an altitude of 6,500 ft mean sea level (msl), the commercial pilot initiated a turn to the west. The airplane encountered turbulence, which the pilot presumed to be leeside turbulence from the mountain range. She turned south to find smoother air, but the turbulence intensified, causing a rapid descent. The airline transport pilot attempted to change the radio frequency to the Ontario Airport Control Tower to advise controllers of their need to transition through their airspace to escape downdrafts. Due to the turbulence, he struggled with the radio’s frequency control but eventually established contact.
Descent and Power Loss
By the time contact was made, the airplane had descended to 2,000 ft msl (about 500 ft above ground level). The airline transport pilot asked the commercial pilot to 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. After reaching about 2,300 ft msl, the engine again lost power. The pilot decided to look for a landing area. With limited options, he chose to land on the westbound lanes of a freeway.
Forced Landing and Damage
While maneuvering over a set of trees, just before touchdown, a vehicle appeared under the right wing. The pilot attempted to avoid a collision, and during the maneuver, the airplane landed hard. The forward fuselage sustained substantial damage.
Postaccident Examination
Postaccident examination of the airframe and engine revealed that both fuel tanks and the gascolator contained fuel; the fuel tank vent was unobstructed, and fuel flowed to the carburetor when the fuel tank valve was set to the "BOTH" position. 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, throttle, mixture, carburetor heat, and propeller controls were intact. The bottom spark plug electrodes had light grey deposits and normal wear signatures. No anomalies were found that would have precluded normal operation.
The engine was removed and placed in a test cell with a replacement "Y" manifold. After start, the engine reached operating temperature but would not accelerate beyond 1,200 rpm. The carburetor was replaced, after which the engine operated normally throughout its speed range.
Carburetor Examination
The accident carburetor was a Marvel-Schebler model MA-4-5. Maintenance logbooks indicated it was rebuilt and installed during an engine overhaul in September 1998, 288.4 flight hours before the accident. No further maintenance had been performed on the carburetor assembly except replacement of the carburetor heat airbox hardware, 27.8 flight hours after overhaul.
Upon disassembly, the brass floats (date stamped May 1997) were intact with no evidence of leaks. Examination revealed that four 1-inch-long studs had been used to mount the airbox assembly to the carburetor bowl, with the forward studs appearing to have penetrated about 1/8 inch into the bowl. 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. The fragments had a polished appearance and matched the shape of the bowl housing where the studs had broken through.
Review of the Cessna illustrated parts catalog showed that the correct hardware for mounting the airbox to the carburetor was four MS20074-04-3 bolts, each 0.4690 inches long, not the 1-inch studs that were used.
Further examination of the carburetor at Marvel-Schebler's facilities, under FAA oversight, revealed additional metallic particles within the fuel mixture metering sleeve, along with scratches and abrasions on the sides of the float.
Probable Cause
The investigation did not explicitly state a probable cause.