- 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
Photo of Beechcraft Model 35, similar to accident airplane
History of Flight
The accident flight was a charter flight from Mason City, Iowa to Fargo, North Dakota. Prior to the flight, and beginning at approximately 1730 on February 2, the pilot began checking weather information for the route of flight. Weather briefings included the local Mason City area, Minneapolis, Redwood Falls, and Alexandria, Minnesota, and the terminal forecast for Fargo. During this initial check, the pilot was advised that all stations were reporting ceilings of at least 5,000 feet and visibility of ten miles or more. The Fargo terminal forecast indicated the possibility of light snow showers after 0200 February 3 and passage of a cold front at about 0400. The pilot was also made aware that a later terminal forecast would be available at 2300. At 2200, and again at 2330, the pilot repeated his weather checks. During the 2330 check, he was advised that the stations en route were reporting ceilings of at least 4,200 feet with visibility still ten miles or greater. Light snow was reported at Minneapolis. The cold front previously forecast to pass Fargo at 0400 was now forecast to pass there at 0200. The Mason City weather was a measured ceiling of 6,000 feet, overcast skies, and visibility of greater than 15 miles. Temperature was reported as 15 degrees F with a dew point of 8 degrees F. Wind was from the south at 25 to 32 knots. Barometric pressure was 29.96 inches of mercury.
Timeline of the flight
At 2355, the pilot made a final weather check. The local weather had deteriorated in that the ceiling had lowered to 5,000 feet, light snow was falling, and the barometric pressure had fallen to 29.90 inches of mercury. Winds remained at 20 knots with gusts to 30 knots. Additionally, at 2335, and again at 0015, the U. S. Weather Bureaus in Minneapolis and Kansas City issued flash weather advisories that called for further deterioration of the weather along the planned route of flight, including reduced visibility, increased winds, freezing drizzle, moderate to heavy icing, and increased snowfall. The pilot was not informed of either advisory during the final weather briefing (by radio) just prior to takeoff at 0055.
The passengers arrived at the airport at about 0040 and the aircraft was prepared for takeoff. During taxi, the pilot made one more weather check via radio. En route weather had not changed substantially, but the pilot was advised that local weather had continued to deteriorate, with ceilings having lowered to 3,000 feet with the sky obscured, visibility of six miles, and a further fallen barometric pressure of 29.85 inches of mercury. Winds remained as previously measured at 20 knots with gusts to 30 knots.
The charter flight performed a normal takeoff at 0055, and once airborne made a left 180-degree turn and climbed to approximately 800 feet. After passing the airport to the east, the airplane then turned in a northwesterly direction, generally along the planned route of flight. Through most of the flight the tail light of the aircraft was plainly visible to a witness, who was watching from a platform outside the Mason City Airport control tower. When the airplane was about five miles from the airport, the witness saw the tail light of the aircraft gradually descend until out of sight. At approximately 0100, when the pilot did not file his flight plan by radio as he had planned prior to takeoff, repeated unsuccessful attempts were made by control tower personnel to contact the airplane.
After an extensive air search, wreckage of the flight was sighted in an open farm field at approximately 0935 that morning. All occupants had been fatally injured and the aircraft was completely destroyed. The field in which the aircraft was found was level and covered with about four inches of snow.
Photo of Beechcraft Model 35 Bonanza N3794N wreckage
The accident occurred in a sparsely populated area, and there were no witnesses to the actual crash. By examination of the wreckage, investigators determined that the first impact with the ground was made by the right wing tip while the aircraft was in a steep right bank, and in a nose-low attitude. Investigators further determined that the aircraft was traveling at high speed on a heading of 315 degrees. The debris field extended over a distance of 540 feet, ending with the main wreckage lying against a barbed wire fence. The three passengers had been thrown clear of the wreckage. The pilot was found in the cockpit. The two front seat safety belts as well as the middle belts in the rear seat were torn free from their attach points. The two rear outside belt ends remained attached to their respective fittings, but the buckle of one was broken.
Although the aircraft was badly damaged, investigators were able to establish certain facts. There had been no fire. All pieces of the airplane were found at the wreckage site. There was no evidence of inflight structural or flight control failures, and the landing gear was retracted at the time of impact.
During the course of the investigation, the damaged engine was disassembled and examined. Investigators found no evidence of engine malfunction or failure in flight. Both propeller blades were broken at the hub, leading investigators to conclude that the engine had been producing power at impact. Propeller blade pitch was in the cruise range.
Despite the damage to the cockpit, investigators were also able to determine: (excerpted from the accident report)
- "Magneto switches were both in the "off" position.
- Battery and generator switches were in the "on" position.
- The tachometer r.p.m. needle was stuck at 2200.
- Fuel pressure, oil temperature, and pressure gauges were stuck in the normal or green range.
- The attitude gyro indicator was stuck in a manner indicative of a 90-degree angle.
- The rate of climb indicator was stuck at 3,000-feet-per-minute descent.
- The airspeed indicator needle was stuck between 165-170 mph.
- The directional gyro was caged.
- The omni selector was positioned at 114.9, the frequency of the Mason City omni range.
- The course selector indicated a 360-degree course.
- The transmitter was tuned to 122.1, the frequency for Mason City.
- The Lear autopilot was not operable."
Photo of Beechcraft Model 35 Bonanza crash scene
The Civil Aeronautics Board ultimately concluded that this accident was the result of several factors. First, the pilot was not qualified to operate an airplane in instrument meteorological conditions (IMC). The Air Service from which the airplane was chartered was approved to operate only in visual meteorological conditions; however, the flight was undertaken in conditions where it was likely that instrument conditions would be encountered. The attitude indicator installed on the accident aircraft operated in a manner that presented attitude information in a format that was opposite to other aircraft in which the pilot was familiar. Investigators believed that after encountering instrument flight conditions, he became confused by the instrument, contributing to a loss of control of the airplane. Finally, investigators criticized the weather briefings and speculated that had the weather briefings been more complete, the pilot might have considered delaying or cancelling the flight.
Photo of Mason City Municipal Airport ATCS tower
Photo copyright Mason City Municipal Airport Manager's Office - used with permission
Investigators cited the weather, in combination with the pilot's lack of qualification to fly in instrument meteorological conditions, as a primary contributing factor in the occurrence of this accident. Prior to the accident, weather conditions had been deteriorating, but remained such that flight by visual flight rules (VFR) remained technically possible. Reported ceilings and visibility remained adequate for VFR flight. For several hours prior to the flight, the pilot repeatedly checked the weather at the Air Traffic Communications Station (ATCS). Local weather reports and forecasts remained relatively stable in terms of ceilings and visibility along the route of flight, but actual conditions were slowly deteriorating in Mason City. The overall weather picture showed a cold front extending from the northwestern corner of Minnesota through central Nebraska with a secondary cold front through North Dakota. Weather forecasts called for widespread snow showers associated with these fronts as they moved east. Temperatures along the planned route were below freezing at all levels with an inversion between 3,000 and 4,000 feet. Moisture was present through 12,000 feet, which, in combination with the freezing temperatures, was conducive to icing conditions which were predicted to be moderate to heavy at times. Winds were reported to be 30 to 50 knots.
Photo of Mason City Municipal Airport 1947
Photo copyright Mason City Municipal Airport Manager's Office - used with permission
At 2335, about 90 minutes prior to the flight, the U. S. Weather Bureau at Minneapolis issued a flash weather advisory containing the following information: "Flash Advisory No. 5 A band of snow about 100 miles wide at 2335 from extreme northwestern Minnesota, northern North Dakota through Bismarck and south-southwestward through Black Hills of South Dakota with visibility generally below 2 miles in snow. This area or band moving southeastward about 25 knots. Cold front at 2335 from vicinity Winnipeg through Minot, Williston, moving southeastward 25 to 30 knots with surface winds following front north-northwest with 25 to gusts of 45. Valid until 0335."
At 0015, about 40 minutes prior to the flight, the U. S. Weather Bureau at Kansas City, Missouri also issued a flash advisory consisting of the following information: "Flash Advisory No. 1. Over eastern half of Kansas ceilings are locally below one thousand feet, visibilities locally 2 miles or less in freezing drizzle, light snow and fog. Moderate to locally heavy icing areas of freezing drizzle and locally moderate icing in clouds below 10,000 feet over eastern portion Nebraska, Kansas, northwest Missouri and most of Iowa. Valid until 0515."
The investigation established that neither of these advisories was transmitted to the pilot. Investigators also speculated that if the pilot had been aware of these advisories, and of the rate at which local conditions were deteriorating, he might have elected to cancel or delay the flight. The investigation further stated that the failure to draw these advisories to the attention of the pilot and to emphasize their importance could readily lead the pilot to underestimate the severity of the weather situation.
Additionally, at takeoff, the Mason City barometer was falling, the ceiling and visibility were rapidly deteriorating, and light snow had begun to fall. The investigation further concluded that surface winds and winds aloft were so high that a pilot could reasonably have expected to encounter adverse weather during the estimated two-hour flight.
Snow had already begun to fall in Minneapolis, and the general forecast along the intended route was for continued deteriorating conditions. The accident report states, "Considering all of these facts and the fact that the company was certificated to fly in accordance with visual flight rules only, both day and night, together with the pilot's unproved ability to fly by instrument, the decision to go seems most imprudent." The investigation concluded that with the conditions existing at takeoff, the flight would have almost immediately encountered instrument flight conditions for which the pilot was not properly qualified.
Photo of a Sperry F3 Attitude Gyro
The attitude indicator, a Sperry F3 attitude gyro, was cited by investigators as having been a possible contributor to the accident. The accident aircraft was equipped with high and low frequency radio transmitters and receivers, a Narco omnigator, Lear autopilot (only recently installed and not operable), and a full panel of instruments capable of being used for instrument flying, including the Sperry F3 attitude gyro.
A conventional artificial horizon provides a direct indication of the bank and pitch attitude of the aircraft. The airplane is symbolically depicted by a miniature aircraft and is displayed against a horizon bar (also referred to as a pitch bar.) The operating portion of the instrument is a gimbal mounted ball that rotates as the airplane changes attitude in either the pitch or roll axis. As installed in the accident airplane, based on similar installations of the era, the artificial horizon would have been a simple black ball with an indicated horizon line. At extreme attitudes, (pitch or roll attitudes in excess of approximately 60 degrees) the internal gimbals impinge on instrument case structure and cause the gyro to "tumble," and display incorrect attitude information. Following an event where the gyro tumbled, it can be reset by caging and then uncaging the instrument. A more complete description of a conventional instrument of the time was published in Air Tech Magazine in May 1943, and is available at the following link: (Air Tech Magazine Article).
On more modern instruments, the ball is typically colored brown, or a darker color, on the lower half of the instrument face, to indicate the ground, and blue, or a lighter color, on the upper half, to indicate the sky. The instrument face is also graduated in markings, referred to as a "pitch ladder" to indicate the pitch attitude above or below level flight. For example, if the airplane enters a climb, the airplane symbol appears to climb up the pitch ladder. For a descent, or a pitch attitude below level flight, the airplane symbol moves down the pitch ladder. In fact, the gimbal mounted ball is rotating behind the airplane symbol, but the indication is such that it appears the airplane symbol is moving relative to the background.
Photo of Bonanza instrument panel equipped with conventional artificial horizon (location highlighted), and example of instrument
The Sperry F3 gyro, as installed on the accident aircraft, also provided a direct indication of the bank and pitch attitude of the aircraft, but was mechanized in such a way that pitch indications were exactly opposite from those of a conventional artificial horizon. Color shading was also opposite from a conventional instrument, dark in the upper half and bright in the lower half. Pitch indication was such that if the airplane was pitched nose-up, the airplane symbol would appear to move down the instrument face, rather than up as in a conventional instrument. A more complete description of this attitude instrument was included in a March 1945 article in Flight Magazine. That article can be viewed at this link: (Flight Magazine Article).
Following introduction into service, experience with the Sperry F3 clearly indicated that pilot confusion was common during the transition period of initial use, or when alternating between airplanes equipped with conventional and F3 instruments. Investigators concluded that since the accident pilot had received his instrument training in aircraft equipped with conventional artificial horizons, and since the Sperry F3 is opposite in its display of pitch attitude, it is probable that the reverse sensing could at times result in reverse control action. This would be especially true of instrument flight conditions requiring a high degree of concentration, as would be the case when flying in instrument conditions in turbulence without a copilot. Examination of the wreckage revealed that the directional gyro (heading indicator) was caged (not operating and locked at a fixed heading) and investigators deemed it possible that it was never used during the short flight. If the directional gyro were caged throughout the flight, this could have added to the pilot's confusion.
Comparison of the Sperry F3 Atitutde gyro versus artifical horizon
An animation of the accident flight path and a comparative illustration between a Sperry F3 attitude gyro and a conventional artificial horizon is available at the following link: (Bonanza Flight Path Animation).
While not cited by investigators as a contributor in this event, spatial disorientation is a common factor in this type of accident. Spatial disorientation, either as a primary accident cause or as a contributor to loss of control accidents is important to understand. The FAA Civil Aerospace Medical Institute (CAMI) has issued a publication explaining this phenomenon and its effect on pilots. This publication can be viewed at the following link: (Spatial Disorientation).
CAMI has also produced a full-length video on the subject of special disorientation, and the dangers it can pose during instrument flight. The video can be viewed at the following link: CAMI Spatial Disorientation Video.
Photos of memorials placed at the accident site
In 1989, a stainless steel monument that depicts a guitar and a set of three records bearing the names of the three celebrities killed in the accident was placed at the accident site. In February 2009, a second memorial for the pilot, depicting a pair of pilot wings, was also placed at the accident site. The two monuments are within a few feet of each other and near the site where the airplane wreckage was found.
The investigation concluded that "At night, with an overcast sky, snow falling, no definite horizon, and a proposed flight over a sparsely settled area with an absence of ground lights, a requirement for control of the aircraft solely by reference to flight instruments can be predicated with virtual certainty."
The accident report states that the pilot, when just a short distance from the airport, was confronted with this exact situation. Instrument fluctuations resulting from the gusty winds would have forced the pilot to focus his attention on the attitude gyro, an instrument with which he was not completely familiar. He was unaccustomed to the reversed pitch display of the attitude gyro, and therefore could have become confused when trying to respond to gust-induced flight path instabilities. The investigation further cited the inadequate weather briefings that should have identified the significantly adverse conditions for the flight.