History of Flight
On February 12, 2010, at 1355 Central Standard Time, a Piper PA-31T (Cheyenne II) turboprop airplane, registration N250TT, impacted terrain while on final approach to runway 33 at Forest City Municipal Airport (FXY) in Forest City, Iowa. The pilot was the sole occupant and was fatally injured. The flight was operated by Mayes Aviation, LLC under 14 CFR Part 91 on an instrument flight plan, departing Spirit of St. Louis Airport (SUS) at 1223. Visual meteorological conditions prevailed.
Several days before the accident, on February 9, the aircraft arrived at FXY with passengers. The pilot reported to multiple individuals that he experienced a vibration in the rudder system with the autopilot engaged. After consulting his mechanic, he repositioned the aircraft to SUS for maintenance. An Aero Charter Jet Center examination attributed the vibration to a faulty rate gyro requiring replacement. However, due to weather, the replacement part was not delivered by February 12. The pilot signed a work declined form noting the rate gyro had an open signal path to the output-hi pin connector. A test flight with an avionic technician showed no autopilot anomalies. The pilot then had the aircraft refueled with Jet-A and prepared for the accident flight.
According to ATC documents, the pilot obtained an IFR clearance to FXY. After departure, the flight proceeded via the OZARK 3 departure to SCHMD intersection, then climbed to FL240. The pilot requested and was cleared direct to SCHUM intersection (an IAF). The flight subsequently descended, and at 1336, the pilot requested an altitude block between 7,000 and 9,000 feet msl to perform an autopilot correction. At 1339, the flight was cleared for the RNAV/GPS Runway 33 approach. Radar contact was lost at 1343 at 4,300 feet msl. At 1345, the pilot reported being established inbound and requested descent to 3,000 feet. At 1353, he reported the airport in sight and was cleared for a visual approach, but did not acknowledge the clearance or make further transmissions.
The airport manager at FXY observed the airplane on final approach. He stated it was on a normal approach when it suddenly veered sharply left and made a rapid descent. He heard engine whine followed by a loud thud. The aircraft impacted terrain about half a mile south of the runway threshold.
Personnel Information
The pilot, aged 66, held an airline transport pilot certificate with single- and multi-engine land and instrument ratings, and was type-rated in the Cessna 500. He also held a flight instructor certificate. His most recent second-class medical certificate was issued April 21, 2009, with a corrective lenses restriction. No previous accidents, incidents, or enforcement proceedings were recorded.
According to his last logbook entry on January 11, 2010, the pilot had 10,352 total flight hours, 8,160 as pilot-in-command, and 113 hours in the accident airplane. He had flown 34 hours in the accident airplane since the last logbook entry per an airplane flight log found in the wreckage. His most recent flight review and instrument competency check were completed in February 2008.
Aircraft Information
The accident airplane was a 1978 Piper PA-31T (Cheyenne II), serial number 31T-7820050, powered by two Pratt & Whitney PT6A-28 turbine engines and McCauley propellers. Its maximum takeoff weight was 9,050 pounds. The airframe had 9,047.6 total hours at the accident, with engines and propellers overhauled in spring 2005 and having 1,023.3 hours since. The aircraft was maintained under a manufacturer inspection program; the last event inspection was on February 3, 2010. The autopilot system was a Bendix King KFC-300 three-axis system.
Meteorological Information
At accident time (1355), the Forest City ASOS reported wind from 110° at 3 knots, visibility 2.5 miles, overcast ceiling at 4,600 feet, temperature -6°C, dew point -8°C, and altimeter 30.01 inches. At 1345, ground visibility ranged from 1.5 to 4 miles due to light snow.
Wreckage and Impact
The initial impact point was about half a mile south of the runway 33 threshold in an open, snow-covered field. The wreckage debris path was 220 feet long on a 290° heading. The fuselage separated into two sections forward of the main cabin. Both engines were attached to their nacelles and exhibited internal circumferential rubbing and scoring, consistent with operation at impact. Both propellers had separated and showed S-shaped bending and twisting. The landing gear was extended. No evidence of pre-impact structural failure was found; all separations were consistent with overstress or recovery cutting.
Medical and Pathological Information
An autopsy performed on February 13, 2010, attributed the pilot's cause of death to multiple blunt force injuries. Toxicological tests by CAMI detected 0.039 ug/ml of Zolpidem (Ambien) in blood and Zolpidem in liver. No carbon monoxide, cyanide, or ethanol were detected. The pilot's overnight bag contained prescription Zolpidem and Benzonatate (Tessalon) and over-the-counter remedies. The pilot had not reported taking prescription medication on his latest medical application.
Tests and Research
Examination of the autopilot system found no elongation of annunciator panel filaments, consistent with the autopilot not being engaged at impact. The pitch, roll, and yaw axis servos functioned during bench testing. The yaw servo exhibited an intermittent tach feedback output that could cause oscillation at one hertz, similar to the rudder vibration reported earlier. The yaw rate gyro had an open signal path to the output-hi pin connector, matching the pre-existing fault. The rate gyro rotor initially did not spin and was misaligned; it functioned after realignment.