What happened
While operating in level cruise at flight level 220, the pilot of a Cessna 172 heard a loud whistling noise and observed that the right side attitude indicator appeared tilted. While attempting to adjust the instrument, the pilot realized the aircraft had entered a dive. The pilot successfully leveled the wings and recovered from the dive at flight level 190. Following the descent, the autopilot was re-engaged, and the flight continued to the intended destination without further incident.
The investigation
A visual examination of the aircraft following the event revealed that the left front baggage door was open and buckled. Additionally, both the left and right wings exhibited skin damage and wrinkling approximately 54 inches from the wing roots.
Testing of the autopilot and flight director systems showed they performed within specifications, with only minor deviations noted. Both vacuum pumps were found to be operating within test specifications. However, the right side attitude indicator continued to display a three-degree turn even after a kink in the vacuum supply was removed. The static system was found to be leaking in excess of allowable limits, though it was noted that the valve had been left in the alternate position prior to testing.
During the inspection, an active noise-canceling headset was found connected to the pilot's side of the cockpit. While the autopilot disconnect tone functioned normally at idle power, it was noted during testing that the tone was difficult for the pilot to hear while wearing the headset.