- Beechcraft Model 35 Bonanza near Clear Lake, Iowa
- Accident Overview
- Accident Board Findings
- Accident Board Recommendations
- Relevant Regulations / Policy / Background
- Prevailing Cultural / Organizational Factors
- Key Safety Issue(s)
- Safety Assumptions
- Resulting Safety Initiatives
- Airworthiness Directives (ADs) Issued
- Common Themes
- Related Accidents / Incidents
- Lessons Learned
- Beechcraft Model 35 Bonanza near Clear Lake, Iowa
Technical Related Lessons
Flight using visual flight rules (VFR) requires a continuous awareness of the horizon. Pilot loss of an external horizon reference, for even a few seconds, can often result in sensory illusions and correspondingly incorrect control inputs. This can rapidly lead to aircraft attitudes from which recovery is difficult or impossible. (Threat Category: Unintended VFR to IMC)
- The pilot in this accident was not qualified to fly with sole reference to airplane instruments. The flight was predicated on weather forecasts that indicated conditions conducive to VFR flight. In fact, weather conditions deteriorated prior to the flight, and associated weather briefings to the pilot did not present a complete picture of the actual conditions. Investigators believed that shortly after takeoff, the pilot encountered conditions that would have required flight with reference to instruments only, for which he was not qualified, and quickly lost control of the airplane, resulting in the accident.
Common Theme Related Lessons
Primary attitude flight displays should not be ambiguous or inconsistent relative to the three-dimensional external environment (up, down, left, right). Lack of familiarity with specific flight instruments intended to allow flight in instrument meteorological conditions (IMC) can lead to confusion and, potentially, to incorrect control inputs and/or loss of control. (Common Theme: Unintended Effects)
- The Sperry F3 gyro horizon, as installed on the accident airplane, was a new design for an artificial horizon, including a feature in which the pitch display was reversed relative to a conventional artificial horizon. The face of the instrument was well marked, and used different colors to depict the sky and ground, which would aid in differentiating up or down pitch indications, but was considered by investigators to be potentially confusing.
Pitch indication convention had been that when climbing, the pitch bar is in the upper half of the instrument, above the indicated horizon. For descents or dives, the pitch bar is below the horizon. The Sperry F3, for a climb, would show a pitch bar below the instrument horizon, and display the opposite for a dive. Investigators concluded that for a pilot not qualified to fly solely with reference to instruments, who was also unfamiliar with the Sperry F3, inadvertent flight into IMC conditions, and transition to reference to the unfamiliar indicator, could have been confusing and lead the pilot to make pitch inputs opposite to those that were actually required to maintain level flight.
- On the accident flight, investigators determined that the pilot flew into IMC conditions almost immediately after takeoff, and though he intended to remain VFR, would have been required to transition to flight by reference to airplane instruments for which he was not qualified. Investigators further stated that the pilot was unfamiliar with the Sperry F3, and could have become confused by its reversed pitch sensing, causing him to make incorrect pitch control inputs and lose control of the airplane.
Comprehensive, complete, and current weather briefings, especially in cases of marginal or deteriorating conditions, are essential to the safe conduct of a flight. (Common Theme: Organizational Lapse)
- Beginning as early as 1730 the afternoon prior to the flight, the pilot began checking weather forecasts and current conditions at the Air Traffic Communications Service (ATCS) at Mason City airport. He received multiple weather briefings over the hours prior to the flight, including a final briefing during taxi just before takeoff. At each briefing, he was supplied with weather information indicating that VFR conditions were present, and would continue to exist for the planned duration of the flight and over the planned flight route.
However, at 2335, a flash weather advisory was issued by the U. S. Weather Bureau in Minneapolis, and at 0015, another was issued by Kansas City, both indicating rapidly deteriorating conditions, including visibility less than that required for VFR flight, and the presence of snow and inflight icing. The ATCS communicator did not provide this information to the pilot, who was therefore unaware of the changed weather conditions.
Investigators stated that the ATCS communicators had the responsibility to provide all available weather information, and to interpret that information, if requested. Investigators concluded that the preflight weather briefings had been inadequate, and were a contributing factor to the accident, in that, had the pilot been made aware of the changed conditions, he might have cancelled or delayed the flight until improved weather conditions existed.