What happened
While cruising at flight level 210 under instrument flight rules (IFR) amidst turbulence, the aircraft began drifting from its intended course. Around 16:00 CST, the aircraft experienced unobserved changes in heading. At 16:10:09, the pilot reported a failure of the gyroscope. Shortly thereafter, the pilot communicated that all flight instruments had been lost and requested vectors for visual flight rules (VFR) conditions. During this period, the pilot indicated the crew was in distress due to a total loss of vacuum pressure, after which all radio contact ceased.
Following the loss of instrumentation, the aircraft entered a steep, right-hand descending spiral. The aerodynamic forces during this maneuver caused the left outer wing panel to separate from the structure, impacting the left stabilizer. The aircraft subsequently crashed, with debris distributed across a four-mile area.
Findings
Post-accident examination of the aircraft showed that the engine, electrical systems, flight controls, and both the pitot-static and vacuum systems remained functional and exhibited continuity. There was no evidence of a malfunction that would have caused hypoxia or a loss of cabin pressure. Investigators determined that the HSI heading card failure is a critical factor, as it can occur without the corresponding heading flag appearing to alert the pilot of the error.