Rangeley, ME, USA
N747AW
Piper PA-46-500TP
With the autopilot engaged, and while climbing through approximately 5,000 feet msl, the pilot moved the heading bug 30 degrees to the right. The airplane then "sort of snapped with significant yaw," into a 60-degree right bank and lost about 1,800 feet of altitude. After recovering, the pilot continued to his destination. Examination of the airplane revealed that it was substantially damaged. Approximately five months prior to the accident, the autopilot system had been installed. Following the installation, the pilot experienced operational problems that included a "yaw problem" which began to worsen, but could not be duplicated by maintenance personnel. A postaccident examination of the autopilot and heading system also revealed no anomalies. Examination of the aft fuselage and tailcone revealed that the yaw damper was contaminated with oil. The source of the oil was an oil streak that ran from under the engine cowling aft along the belly of the airplane, and then up through the air conditioning exhaust vent. Two other airplanes which experienced yaw damper events were also examined, and oil contamination of the yaw damper amplifiers were identified.
HISTORY OF FLIGHT On September 12, 2005, about 0930 eastern daylight time, a Piper PA-46-500TP, N747AW, was substantially damaged while recovering from an in-flight upset, 15 miles southwest of Steven A. Bean Municipal Airport (8B0), Rangeley, Maine. The certificated private pilot and the two passengers were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight destined for Lehigh Valley International Airport (ABE), Allentown, Pennsylvania. The flight was conducted under 14 CFR Part 91. According to the pilot, the autopilot was engaged in "heading bug mode," and the airplane was climbing at approximately 700 feet per minute. About 15 miles southwest of Rangeley, while climbing through approximately 5,000 feet msl, in "light chop" above mountainous terrain, the pilot moved the heading bug 30 degrees to the right to remain clear of clouds. The airplane then "sort of snapped with significant yaw," into a 60-degree right bank. After overpowering the autopilot and recovering from uncontrolled flight, the pilot turned the airplane through two 360-degree turns, and climbed to 16,500 feet. About 20 to 25 miles southwest of Rangeley he requested flight following from air traffic control, and continued to Allentown without further incident. The pilot estimated during the upset that the airplane had lost 1,000 to 1,800 feet of altitude, and could not remember if the autopilot disconnected during the upset or the recovery to controlled flight. The accident occurred during the hours of daylight, about 44 degrees, 46 minutes north latitude, and 70 degrees, 47 minutes west longitude. PERSONNEL INFORMATION The pilot held a private pilot certificate with ratings for airplane single and multi-engine land, and instrument airplane. He reported a total flight time of 1,327.4 flight hours, and 224.8 hours as pilot in command in the accident airplane make and model. His most recent FAA third-class medical certificate was issued on May 16, 2005. AIRCRAFT INFORMATION The airplane was manufactured in 2000 and was originally equipped with an S-TEC 550 autopilot system. At the time of the accident, the airplane had accrued 1,227.3 total hours of operation. According to logbook entries and correspondence to the Safety Board by the owner, on March 24, 2005, a new S-TEC MAGIC 1500, autopilot system was installed. This installation included a new programmer computer, yaw amplifier, yaw servo, data converter, and an autopilot master switch. On April 1, 2005, the airplanes most recent annual inspection was completed. Seventeen days later, the pilot advised the maintenance provider that the roll rate on the heading bug was "fast," as compared to the previous autopilot, and that he was not sure the autopilot was operating properly. Sometime during the week of May 9, 2005, the yaw servo and rudder trim were adjusted by the maintenance provider. On June 23, 2005, the pilot reported that the "yaw problem" began to worsen. On July 3, 2005, the pilot encountered a "severe yaw" when the autopilot was "released," and the flight director bars would not work when the flight director mode was selected. The pilot also stated he requested the original "550" autopilot be reinstalled at that time. On July 11, 2005, the maintenance provider attempted to troubleshoot the autopilot problem. The wires were checked between the autopilot computer and trim monitor, pilot and copilot's trim switches, trim master switch, pitch and pitch trim servos, with no anomalies noted. The autopilot computer was removed, a loaner unit was installed for test purposes, and no anomalies were noted. A new unit was then installed, and operationally checked. The yaw damper amplifier was also removed and replaced with a new unit, and was operationally checked. METEOROLOGICAL INFORMATION The reported weather at Berlin Municipal Airport (BML), Berlin, New Hampshire, 33 nautical miles southwest of Rangeley, at 1352, included: winds from 300 degrees at 9 knots, gusting to 16 knots, visibility 7 miles, overcast skies at 3,400 feet, temperature 72 degrees Fahrenheit, dew point 57 degrees Fahrenheit, and an altimeter setting of 29.96 inches of mercury. WRECKAGE AND IMPACT INFORMATION A postaccident examination of the airplane revealed that the airplane's wings were damaged during the event. Multiple wrinkles on both wing upper surfaces were noted extending from the wing roots outboard for approximately 43 inches, and on both wings, the wrinkles terminated at a wing production splice. Engine Examination Examination of the engine revealed no evidence of malfunction. The engine condition trend monitoring data was downloaded for review, and no engine faults were recorded for the accident day. Interior Examination Examination of the airplane's interior revealed that the Federal Aviation Administration (FAA) approved pilot operating handbook (POH) for the airplane, which contained the autopilot airplane flight manual supplement, was located in a cabinet drawer behind the copilot's seat. Further examination of the interior revealed two checklists labeled: "FOR TRAINING USE ONLY," located in a sidewall storage pocket on the copilot's side of the cockpit. Both of the checklists did not contain any information associated with the autopilot installed in the airplane at the time of the accident. In addition, there was a yellow tie wrap fastened to the pitch trim circuit breaker. Primary and Secondary Flight Controls Examination The flaps, left and right ailerons, left and right elevators, and rudder were intact and undamaged. Flight control continuity was confirmed for all control surfaces, all control cable tensions were within specified tolerances, and control travel for all surfaces was verified to be within specifications. No problems with binding, routing, or wear was evident. The elevator trim system, rudder trim system, and ground-adjustable aileron trim tab were examined. Functional checks were performed and no anomalies were noted. The aileron trim tab was present on the right aileron and all fasteners were secure. Autopilot and Heading System Examination Examination of the autopilot and heading system revealed that all system components were found to be installed as per the manufacturer's manuals and drawings with the exception of the air data attitude heading reference system (ADAHRS) wiring harness, which had been modified to help calibrate the magnetic heading portion of the electronic flight instrumentation system (EFIS). All bridle cable tensions were found to be within specified tolerances and no problems with binding, routing, or wear was discovered. Functional checks of the autopilot system were performed utilizing the manufacturer's ground maintenance tests procedures and the POH. No evidence of malfunction or anomalies was discovered, and no defects with the autopilot or EFIS were noted. Simulations of several in-flight failures revealed that all autopilot disconnect functions were working. Disconnects would occur during simulated heading and ADAHRS failures, or during loss of data. All inputs from the pilot's primary flight display (PFD) and navigation display (ND) units functioned properly. Manual disconnects of the autopilot system, yaw damper system, and pitch trim system was performed utilizing the emergency procedures contained in the airplane flight manual supplement for the autopilot. No anomalies were noted, and all disconnect functions worked. Ability to manually override the autopilot was checked utilizing one hand on the pilot's control wheel, and the roll and pitch servos override limits were within specifications. The rudder servo was also overridden, and no unusual noise or feel was noted when overriding any of the autopilot servos. All electronic audio alerts annunciated correctly and in proper sequence, and electronic altitude callouts were functional. After all the previously listed actions regarding the autopilot and heading systems were performed, the autopilot was removed for qualification testing. No anomalies were discovered during the tests. Aft Fuselage and Tailcone Examination Examination of the aft fuselage and tailcone on the airplane revealed evidence of oil staining and oil splatter marks. Further examination revealed that the source of the oil was a streak that ran from under the lower portion of the cowling aft along the belly of the airplane, and up through the air conditioning exhaust vent. Examination of the yaw damper amplifier, which was mounted on an internal bulkhead above and aft of the air conditioning exhaust vent, revealed that the bulkhead and yaw damper amplifier also exhibited evidence of oil staining. TESTS AND RESEARCH Autopilot Usage According to the pilot, he had operated the "new" autopilot system approximately 25 times. He had not received any training on the use of the new autopilot system, nor was any offered. Just prior to the event he could not remember which "LEDs" (engage annunciators) were illuminated. When specifically questioned about observations made by the investigative team, the pilot advised that the yellow tie wrap that was fastened to the pitch trim circuit breaker, was placed there by his instructor because, "you have seconds to react if the pitch trim has a problem." The pilot added that the autopilot had a built in self-test that initiated when he turned on the master switch, and that he noticed no anomalies with the autopilot during startup, taxi, or takeoff. Besides the self-test, no other checks of the autopilot were performed. When asked about the checklists the investigative team discovered in the copilot's sidewall storage pocket, the pilot stated that they were "used as his primary reference." MAGIC 1500 Failure Modes and System Protections A review of the MAGIC 1500 autopilot system revealed that it had multiple built in protections for trim runaways, hardovers, softovers, and multi-axis hardovers. System protections were automatic in the event a failure occurred while the autopilot was engaged. No immediate action items were required to be accomplished by the pilot. Autopilot POH Supplement A supplement to the POH was included for the MAGIC 1500 Autopilot. A review of this document, which was found in the POH onboard the airplane, contained information about system functions, controls, preflight, and in-flight procedures. A six page "pre-flight procedures" checklist for the autopilot system was included. Autopilot Familiarization According to the maintenance provider who installed the autopilot, they discussed completing a one to two hour flight with the pilot in order to familiarize him with the functions of the new autopilot. Due to the timing of some parts shipments, the completion date of the airplane was not compatible with the pilot's schedule. Rather than "wait an additional day or two," the pilot elected to have the airplane delivered to him. Other Yaw Damper Events The Safety Board was also notified of two other yaw damper events. One involved a "left hardover" after the pilot engaged the autopilot, and the other, was a "pitch" oscillation that occurred during a climbing turn after the pilot selected a new heading via the heading bug. Examination of the interior of the aft fuselage and tailcones in both airplanes revealed evidence of oil staining and oil splatter, above and aft of their air conditioning exhaust vents. Both the internal bulkheads and yaw damper amplifiers were contaminated with oil, and in one instance, evidence of water intrusion associated with washing of the airplane was also identified. ADDITIONAL INFORMATION In all, including the previously mentioned occurrences, the Safety Board identified five yaw damper events. These included reports of rudder pedal pulsing, shaking, oscillations, and uncommanded movement. Corrective Actions The airplane manufacturer issued Service Bulletin No. 1170 on October 6, 2006, requiring installation of a louvered cover (Piper Kit 767-545) to "direct air flow out of the tail cone area," minimizing the ingress of liquids (such as water and engine oil) which could lead to contamination and damage of electronic equipment in the tailcone. Wreckage Release The wreckage was released to the owner on October 12, 2005 with the exception of the autopilot computer, which was released on December 20, 2005.
A malfunction of the yaw damper system due to fluid contamination. Factors in the accident were the air condition exhaust vent design and the design stress limits of the airplane were exceeded.
Source: NTSB Aviation Accident Database
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