History of Flight
On September 28, 2021, about 0900 central daylight time, a Rockwell International 690B airplane, registration N690LS, was destroyed when it crashed near Hiles, Wisconsin. The pilot and two passengers sustained fatal injuries. The flight was operated as a Title 14 Code of Federal Regulations Part 91 aerial imagery survey flight for the Wisconsin Department of Natural Resources.
According to ADS-B and ATC data, the airplane departed Rhinelander-Oneida County Airport (RHI) at about 0850. Approximately 8 minutes later, it leveled off at about 16,100 ft and accelerated to a maximum groundspeed of 209 knots. Between 0858 and 0900, groundspeed decreased to about 93 knots, and the airplane descended about 500 ft while on a steady northeasterly heading. The airplane then made a right turn with a rapid descent, and ADS-B data ended at 0900:56. ATC audio captured transmissions of "mayday, mayday, mayday" and "we’re in a spin."
A witness about 1 mile from the accident site reported hearing a "loud, strange sounding airplane" and saw it "nose down at high rate of speed spinning about its longitudinal axis at about 30 to 60 rpm." The witness lost sight of the airplane behind trees and then heard an impact.
Personnel Information
The pilot's logbook was not located. According to training records provided by the operator, on February 5, 2021, the pilot successfully completed Turbo Commander 690B ground and simulator training (10.0 hours) with SIMCOM Aviation Training. Additionally, on March 19, 2021, the pilot completed 40.9 flight hours in the operator’s Aircraft Familiarization and Pilot Qualification Mentoring Program.
Aircraft Information
Maintenance records indicated the airframe’s most recent inspection was a 150-hour periodic inspection performed on September 24, 2021, at a total time of 7,854.7 hours. The 150-, 200-, and 300-hour inspections were performed on both engines.
In July 2021, the pilot performed an in-flight shutdown of the right engine and a single-engine landing due to a reported torque hang-up at 300 HP with the power lever at flight idle. Maintenance could not duplicate the problem and replaced the engine fuel control unit and fuel inlet sensor with overhauled components. No further maintenance was performed on the right engine between July and September 24, 2021.
The airplane was equipped with a Collins AP-106 Flight Control Systems autopilot, offering modes including heading, navigation, altitude hold, and indicated airspeed hold. Its stall warning system consisted of a warning horn and a switch on the right-wing leading edge, factory-adjusted to close between 4 and 9 knots above stall speed. According to the Pilot’s Operating Handbook (POH), the stall speed with landing gear and flaps retracted at gross weight was 82 KCAS, and minimum controllable airspeed was 86 KCAS. The POH did not include a procedure for recovery from an inadvertent spin and stated that "acrobatic maneuvers, including spins, are unauthorized."
Wreckage and Impact
The wreckage was located in remote wetlands and wooded terrain, distributed over an area about 150 ft in diameter. Most of the main wreckage was highly fragmented and submerged; other debris was in adjacent trees. The forward fuselage, fragmented wing sections, and a portion of the rear fuselage were submerged. A smell of Jet A fuel and a sheen on the wetlands were noted.
The cockpit and fuselage were crushed aft and fragmented by impact forces. Flight control cable continuity could not be established due to fragmentation; all connections exhibited tensile overload fractures. Primary and secondary control surfaces were fragmented within the debris field.
Examination of both engines revealed damage consistent with rotation and operation at impact. Propeller blades on both sides showed aft bending and twisting to a low-pitch position, with butt impact marks indicating aft loads consistent with a low blade angle, low power, and a steep impact angle.
Additional Information
An aircraft performance study largely based on ADS-B data showed that at 0900:38.7, the airplane pitched down more than 30° and descended at up to 20,000 ft per minute. At that time, the estimated normal load factor decreased from about 1.6 G to less than 1 G. The study stated that a decrease in normal load factor is consistent with a stall when the wing reaches its critical angle of attack, and that a spin could result if the airplane were in uncoordinated flight at the time of a stall.
The airplane was certificated under Civil Air Regulations Part 3 for normal-category operations, intended for non-aerobatic, nonscheduled passenger and cargo operations. For this category, manufacturers are not required to include spin recovery procedures in the POH, but a placard against spins is required. The accident airplane’s placard was on the left side of the instrument panel. The POHs for the 690C and 690D models include spin recovery procedures, but the reason for the difference was unclear. According to GAMA Specification No. 1, inclusion of spin recovery procedures in multi-engine airplane POHs is largely at the manufacturer’s discretion.