NTSB Factual Report

On May 30, 2001, approximately 1855 Pacific daylight time, a Cessna 172S, N571SP, registered to R & D Leasing of Oregon, Inc., Hillsboro, Oregon, and operated by Hillsboro Aviation Inc. of Hillsboro, Oregon, experienced flight control difficulties while in climbing flight at an altitude of about 4,500 feet on a 14 CFR 91 instrument flight rules (IFR) instructional flight from Eugene, Oregon, to Hillsboro, Oregon. As a result of the flight control difficulties, the pilots performed an off-airport precautionary landing in a plowed field about 2 miles east of Monroe, Oregon. The pilots accomplished the off-airport landing successfully, without any reported damage to the aircraft, and neither the commercial pilot-in-command of the flight (a certificated flight instructor) nor a private pilot trainee were injured in the incident. Visual meteorological conditions were reported at Corvallis, Oregon, at 1915, and an IFR flight plan was filed for the flight.

According to the pilots' accounts, the flight was cleared to an altitude of 6,000 feet on departure from Eugene, and departed Eugene between 1840 and 1850. The trainee reported that the flight departed behind a Horizon Air F-28 aircraft and received vectors behind the F-28 for wake turbulence avoidance. He stated that the instructor, who was sitting in the right seat, took control during this segment since the trainee was wearing a vision-restricting device and the instructor could keep the F-28 in sight. The trainee reported that as the aircraft climbed through 4,500 feet, "the airplane pitched up, and rolled to the left followed by a pitch down, and a roll back to wings level, then a pitch back up and to the left." The instructor stated that as the aircraft climbed through that altitude, "the aircraft suddenly nosedived for about 3-4 seconds and pitched up into a climb." Both pilots reported that they susbsequently felt the pitch control stuck in a pitch-up position, and that they had to hold forward pressure to hold the nose down (the instructor stated both pilots had to apply full forward pressure to prevent a stall.) The instructor further reported that the aircraft would not roll; the trainee reported that the controls were stuck in roll to the left. The pilots reported that the instructor subsequently attempted to trim the aircraft nose-down, without success (they did not indicate in their written statements to the NTSB whether they attempted to utilize manual or electric pitch trim, but they indicated to an FAA inspector in an initial interview that the manual trim wheel would not turn.) The pilots declared an emergency with ATC and subsequently elected to land in a field directly in front of the aircraft by utilizing rudder and power for control, which they accomplished successfully. The trainee reported to the FAA inspector that "After we landed we noticed that the controls were free as if something was stuck, and had bounced loose."

The aircraft is equipped with mechanical cable-and-bellcrank-actuated flight controls, and is also equipped with a Bendix/King KAP 140 autopilot system with manual electric pitch trim. According to the aircraft pilot's operating handbook (POH) supplement on the KAP 140 autopilot system, at the time of autopilot engagement the aircraft initially enters vertical speed mode at the vertical speed existing at the moment of autopilot engagement (in the pitch axis), and wing leveler mode (in the roll axis). The POH supplement also states that activating manual electric trim with the autopilot engaged will disengage the autopilot. The pilots reported in their initial interview with the FAA inspector that they did not have the autopilot on at the time of the occurrence, and that they made no attempts to disengage the autopilot during the incident. Post-incident examinations of the flight controls, trim, and autopilot operation by the operator and the FAA inspector did not disclose any evidence of malfunctions or abnormal flight control or autopilot operation.

Following the incident and subsequent troubleshooting by the operator and FAA inspector, the autopilot system components were functionally tested at the facilities of their manufacturer, Honeywell Aerospace Electronic Systems of Olathe, Kansas, under FAA supervision on July 12, 2001. The components tested comprised the KC 140 flight computer, KCM 100 configuration module, KS 270C pitch servo, KS 271C roll servo, and KS 272C pitch trim servo. According to Honeywell's report of this testing activity, the components were tested both as a system (connected together on a system test harness), and individually. The Honeywell test report stated:

...upon completion of all the previously described testing, both as a system

and as individual components, the autopilot system demonstrated compliance

with all of the design requirements and all of the components tested met all of

the required specifications for a new unit. No anomalies were noted during any

phase of the testing that would indicate the system had previously experienced

a failure that might cause autonomous engagement or uncommanded servo drive.

NTSB Probable Cause

A degradation of aircraft control for undetermined reasons.