Analysis of a Stall-and-Spin Accident Using Recorded Avionics Data

Abstract

On August 28, 2006, a Cirrus Design SR22 was destroyed when it impacted a water retention pond located about 2.4 miles from the Eagle Creek Airpark (EYE), Indianapolis, Indiana, after a loss of control during cruise climb. The personal flight departed EYE en route to Hilton Head Island, South Carolina. The pilot received fatal injuries, and the three passengers received serious injuries. Instrument meteorological conditions prevailed at the time of the accident, and the flight was on an instrument flight plan. During the final three minutes of the flight, the airplane decelerated from 118 KIAS to about 90 KIAS over about 30 seconds, and then slowly decelerated to about 74 KIAS over about 2 minutes. At about 74 KIAS, the angle of attack of the airplane exceeded the stall angle of attack of the wing, the airplane banked to the left, and started to descend. Over the next 25 seconds, the airplane continued to “wallow” in a stalled condition, with erratic oscillations in the pitch and roll angles, and with the descent rate rapidly increasing. Finally, about 15 seconds prior to impacting the ground, the airplane entered a left spin and continued descending. About four seconds prior to impact, a large decrease in the longitudinal load factor was recorded, which could be consistent with the deployment of the Cirrus Airframe Parachute System (CAPS) parachute. This accident is still under investigation by the NTSB, and the probable cause of the accident has not yet been determined. To date, however, the investigation has benefitted greatly from flight data recorded by the airplane’s avionics systems. This data has enabled investigators to determine and analyze the motion of the aircraft throughout the accident flight, and the physical forces that produced that motion. In addition, investigators have been able to compare the airplane performance during the accident to the nominal, expected performance of the SR22, as determined from flight tests performed during the investigation. For the flight tests, the test airplane’s standard avionics system was used to collect and record data; consequently, the data recording system, and the data analysis techniques, for both the flight-test airplane and the accident airplane were identical. The lift and drag coefficients of the accident and flight test airplanes were computed from the recorded data, and indicate that the performance of the accident airplane was consistent with the nominal performance of the SR22. This case demonstrates how the data recording capabilities of modern avionics systems can assist accident investigations and contribute to aviation safety, extending to the general aviation population the safety benefits that flight data recorders have brought to the transport category fleet.