Clues, no cause in Sauk Rapids plane crash… yet

Firefighters work to get the flames under control after a small plane crashed into a home at 731 Garden Place in Sauk Rapids, Minn., Friday, June 20, 2014.  Jason Wachter | St. Cloud Times via AP

The National Transportation Safety Board has been unable — so far — to figure out what caused a plane to crash into a Sauk Rapids, Minn., house last June, killing the pilot and the German exchange student who was getting a sightseeing flight over St. Cloud.

The NTSB didn’t eliminate the possibility that the plane — an experimental RV-6 — was thrown by the wake turbulence from an Allegiant Airlines plane landing at St. Cloud airport; it said there was no way to know.

The report issued this week is a “factual report,” not the conclusion that will be revealed in the “probable cause” report still to come.

But the factual report, raised the possibility that the plane’s canopy came unlatched, citing tests from a different model of airplane.

The Lancair Legacy Canopy Safety Issue (Thorn 2014) discusses accidents resulting from flight with the upward opening canopies that become unlatched/open in flight for Lancair and not RV airplanes, which also have upward opening canopies. The paper states in part:

“There are several potential root causes of the Legacy’s open canopy flight hazard. One is the canopy is large and, if not latched down in flight, it will open to varying degrees and alter the air flow over the tail/stabilizers and under some situations create significant pitch attitude stability and control issues.

Another potential root cause may be the pilot’s loss of reliable airplane pitch attitude reference where the canopy’s structural frame serves as a key attitude reference line and as the open canopy moves it corrupts the pilot’s normal visual pitch attitude reference cues.

This is not likely. First the RV model of airplane (I built and fly an RV airplane) has two — not one — latches to keep the canopy closed. And the NTSB acknowledges that all of the mechanism was destroyed in the resulting fire. The fact a headset case was found in a neighboring house does, however, suggest a canopy opened.

Second, pilots of RV airplanes don’t use a canopy frame as a reference line.

Far more likely — if the canopy is involved at all — is this addition to the NTSB report.

There may also be a tendency for pilots flying with the shock and chaos of an open canopy, with severe cockpit wind, noise, and debris flying about, to induce pitch attitude oscillations by their control inputs.”

This is the cause of many airplane accidents. The plane can fly just fine with a canopy half-latched. But pilots often turn their attention to closing it, are distracted, and forget to — as the saying goes — “fly the airplane.”

Killed in the crash were pilot Scott Olson, 60, and Alexander Voigt, 16, who was staying with St. Cloud Mayor Dave Kleis. He was set to return to Germany the following week.