It’s still IMC

This made a well-coordinated graveyard spiral indistinguishable from straight-and-level flight until the pilot escaped the clouds, often too late to recover. Organizational pressure to fly in all weather without the equipment to make that feasible resulted in an extremely high accident rate.

And despite successive waves of technological advances, the risk of spatial disorientation remains with us. Descendants of the experimental gyroscopic attitude instruments pioneered in the 1920s became standard in most light-airplane panels by the 1960s, then were eventually supplanted by solid-state air data sensors feeding electronic flight displays. Autopilots jumped from the airlines to civilian market during that same period. The initial ground build-out of nondirectional beacons and four-course ranges gave way to a nationwide VOR network and ILS capabilities at most towered fields. In the 25 years since the first aviation GPS was certified for use under instrument flight rules, augmentation systems such as WAAS have sharpened its resolution of location and altitude dramatically.

And yet, experienced pilots in well-equipped aircraft still lose their lives flying into clouds, fog, or over water at night.

A case in point

On September 23, 2017, a Mitsubishi MU–2B-40 was destroyed moments after taking off into a 500-foot overcast from the Ainsworth Regional Airport in Nebraska. The solo pilot was killed. The accident site was about three and a half miles northeast of the airport, to the right of his planned route to Bottineau, North Dakota. According to the NTSB’s final report, “The airplane was massively fragmented during the impact and debris was scattered for about 300 feet. The damage to the airplane and ground scars at the accident site were consistent with the airplane impacting in a left-wing-low, nose-low attitude with relatively high energy.” The report goes on to describe physical evidence “consistent with both engines producing power and both propellers developing thrust at the time of impact.”

Several aspects of the accident sequence seem odd. The pilot—described by his long-time airplane partner as “not a risk-taker”—filed an IFR flight plan while driving to the airport but declined a weather briefing. He subsequently took off without obtaining his IFR clearance. The NTSB report notes that the airport’s ground communications outlet (GCO) was out of service at the time. However, there’s no evidence the pilot attempted to contact clearance delivery with the mobile phone he had used to file.

In addition to the GCO, low-altitude radar coverage was also out of service the morning of the flight, so there is no record of the airplane’s actual flight path. Both a Center Weather Advisory for heavy rain and a convective sigmet for embedded thunderstorms were in effect, but National Weather Service radar showed the nearest cells 59 to 75 miles to the east-northeast, with “no significant echoes in the immediate vicinity.” IFR conditions were expected over “an extensive area” covering the route, but his flight plan didn’t specify an alternate airport.

Ample experience

The 69-year-old instrument-rated private pilot was co-owner of the MU–2B. He held privileges for single- and multiengine airplanes and multiengine seaplanes. His make-and-model experience went back to his initial MU–2B training at FlightSafety International in 1999. He had completed recurrent training at SimCom on June 3, just more than three months before the accident, including a full instrument proficiency check (IPC) with unusual attitude recoveries from both “descending VNE” and “ascending stall speed conditions.” His prerequisite form for that course listed 2,850 hours in type and the board estimated his total flight experience at 3,775 hours. (His logbooks haven’t been found.) The only limitation on his third class medical certificate was a requirement for corrective lenses.

His partnership with his co-owner spanned 17 years, during which they’d owned several MU–2s. They had bought the accident airplane in 2006. The partner estimated that they’d flown at least 500 hours together, including their recurrent training sessions, and described him as “always well prepared.” The pilot had “expressed no concerns” during a conversation that morning, and his partner knew of no personal or professional problems that might have pressured or distracted him.

‘Transient’ trouble?

In 2008, the co-owners had replaced the original analog instruments with a two-screen Chelton air data, attitude, and heading reference system display backed up by a stand-by attitude indicator and turn coordinator on the pilot’s side and second attitude indicator on the co-pilot’s side. During that same conversation, the pilot mentioned noticing a “transient” flag associated with the ADAHRS without detailing whether this happened in the air or on the ground. He also left a phone message at their avionics shop advising that he planned to bring the airplane in after the North Dakota flight. Apparently it didn’t worry him greatly; his partner “could not imagine” him taking off with any known anomaly in the aircraft.

Might that flag have been the first flicker of a failure that compromised the panel just after the airplane entered the clouds? The NTSB report notes that the Chelton system “could not be functionally tested.”

The NTSB attributed the accident to spatial disorientation, and it’s hard to construct a better explanation of why a healthy, experienced pilot lost control of a functional, highly capable airplane so quickly. His decision to launch into IMC without a clearance is hard to fathom. But with minimal backup instrumentation, losing the screens for even a few seconds at low altitude in IMC would test the limits of any instrument pilot.