CHI06LA088

The experimental amateur-built airplane sustained substantial damage on impact with trees and terrain during a forced landing. The pilot reported the throttle stuck during cruise flight. The pilot attempted to get the sticking throttle to release and the throttle stuck in idle position. The kit manufacturer's examination of the throttle cable and carburetor concluded: "The throttle cable was not supported/attached to anything from the firewall to the cockpit control knob. There was a large amount of flex in the cable when the control knob was pushed when resistance was applied to the Carb End of the cable. The only anchor on the throttle cable was a "through the firewall" clamp. ... The AeroCarb was disassembled. ... Nothing internally was found that would cause it to stick."

On February 27, 2006, about 1645 central standard time (cst), an experimental amateur-built Irwin Sonex 2180 airplane, N514KP, piloted by a private pilot, sustained substantial damage on impact with trees and terrain during a forced landing near Rockford, Illinois. The personal flight was operating under 14 Code of Federal Regulations Part 91. No flight plan was on file. The pilot reported that he sustained no injuries. The flight originated from the Poplar Grove Airport (C77), near Poplar Grove, Illinois, at 1615.

The pilot's accident report, in part, stated:

Aircraft departed C77 on a personal, recreational flight at

approximately 415 pm cst. Pilot performed several throttle sticking

tests in the immediate vicinity of C77 and all was o.k. Pilot cruised

north of Rockford, IL at approximately 2200 [feet above mean sea

level] at 2800 rpm. Just north of Cottonwood Airport (IC8) pilot

attempted to increase throttle. It stuck. Pilot attempted to get

sticking to release [and] throttle stuck in idle position. Pilot turned

toward Cottonwood but when he determined it was out of range, he

picked the best available corn field. Upon approach, he pulled up

over electrical wires [and] a wind gust pushed the plane into the top

of a tree about 25 [feet] up. After impacting the tree, the plane

stopped forward movement and fell tail first to the ground. ... The

craft then tipped onto its top. Pilot exited through broken canopy.

A Federal Aviation Administration Inspector and a representative from the kit manufacturer examined the wreckage to include the throttle cable and carburetor. The kit manufacturer stated:

When disconnected from the carb, the Throttle Cable was found to

be quite stiff compared to others Sonex Aircraft, LLC has experience

with. Note that the owner stated it was smoother prior to the

incident. The throttle cable was not supported/attached to anything

from the firewall to the cockpit control knob. There was a large

amount of flex in the cable when the control knob was pushed when

resistance was applied to the Carb End of the cable. The only anchor

on the throttle cable was a "through the firewall" clamp. ...

The AeroCarb was disassembled. No internal flaws or defects were

found other than some very minor scratches. Nothing internally was

found that would cause it to stick. ...

The Sonex website, www.sonexaircraft.com, was reviewed. The site contains links to service bulletins to include bulletins in reference to sticky throttles.