Atlanta, GA, USA
N46PT
Piper PA 46-350P
The pilot reported that he heard a loud whistling noise while in level cruise at flight level (FL) 220 and noticed that the right side attitude indicator was "tilted." While he was leaning over adjusting the instrument, he realized that the airplane was in a dive. He leveled the wings and pulled out of the dive at FL 190. The autopilot (A/P) was re-engaged and the flight was completed to its intended destination without further incident. A visual examination after the descent revealed the left front baggage door open and buckled, and the left and right wings showed skin damage and wrinkling approximately 54 inches from the wing roots. When tested, the autopilot and flight director performed within test specifications with only "minor" deviations. Both vacuum pumps tested within test specifications. The right side attitude indicator continued to show a three degree turn even after a kink in the vacuum supply to the right side attitude indicator was removed. The "normal" static system leaked in excess of allowable limits; however, the valve was found to be in the "alternate" position before it was tested. An active noise-canceling set of headphones was found connected to the pilot's side of the cockpit. The A/P disconnect tone was found to be operating normally while the engine was at idle power. During the test, it was noted that the tone was difficult to hear while wearing the headset.
On December 3, 2006, about 1114 eastern standard time, a Piper PA 46-350P, N46PT, owned and piloted by a private pilot, arrived with substantial damage at Indianapolis Metropolitan Airport (UMP), Indianapolis, Indiana. The pilot stated that the autopilot disengaged over Atlanta, Georgia, during cruise at flight level (FL) 220. The airplane then entered a "dive" from which he recovered at FL 190. The 14 CFR Part 91 personal flight was operating on an instrument rules flight plan. The private pilot and passenger were uninjured. The flight originated from Page Field Airport, Fort Myers, Florida, about 0823 and was en route to UMP. The pilot stated that he heard a "loud whistling noise" and noticed that the right side attitude indicator horizon was "tilted". He was leaning over the right front pilot seat while "focusing" and "adjusting" the right side attitude indicator horizon. He "soon" noticed that the right side heading indicator was turning. He sat up and "discovered" the airplane was in a "dive." He leveled the wings and pulled out of the "dive" at FL 190. The pilot then requested a climb back up to FL 200, and the flight was completed to UMP without further incident. The pilot reported that he re-engaged the autopilot and it worked "fine" for the rest of the trip. Upon a visual examination of the exterior of the airplane, the left forward baggage door was found open and buckled. Both wings had wrinkles and skin deformation in the upper skin surface approximately 54 inches from the wing roots. The damage to the left wing surface was more pronounced. Bench testing of the autopilot (A/P) computer and the flight director (FD) was conducted. Both units performed properly with only minor deviations. The FD was slow to come on but did stabilize and performed correctly. Both vacuum pumps were tested on the airplane, and operation was found to be normal with 5.1 psi of suction. The right side attitude indicator showed a three degree turn. The vacuum supply hose for the right side attitude indicator was found kinked at the upper outboard instrument panel support. The kink was removed and the right side attitude indicator continued to show a three degree turn. The pitot-static system was tested. The static supply source valve was found in the "alternate" position when the attempt to test and verify the altimeter and A/P altitude hold mode was conducted. The "alternate" static system tested within limits, however the "normal" static system leaked in excess of allowable limits. The A/P altitude hold mode operation tested normal. When simulated flight at FL 220 was conducted, the A/P made correct pitch trim inputs to the stabilizer when 25 foot altitude excursions above and below FL 220 were simulated. An operational check of the A/P and instruments under aircraft power was normal. An active noise-canceling set of headphones was found connected to the pilot's side of the cockpit. The A/P disconnect tone was found to be operating normally while the engine was at idle power. During the test, it was noted that the tone was difficult to hear while wearing the headset.
The exceedance of airplane design stress limits when the pilot did not maintain aircraft control after his attention was diverted to the right side attitude indicator during cruise flight. An additional cause was the aural detection for the autopilot disconnect was difficult to hear with the noise canceling headset. A contributing factor was the disengaged autopilot/flight director.
Source: NTSB Aviation Accident Database
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