Flying low to stay beneath a descending overcast is dangerous business, and rising terrain and obstacles have doomed many a scud-running pilot. Add to the mix the turbulent downdrafts of an intensifying thunderstorm, and disaster is all but assured.
On Aug. 24, 2006, the noninstrument-rated pilot of a Piper PA-28-140 Cherokee flew low over the bogs of eastern North Dakota as weather conditions deteriorated around him. He managed to dodge the obstacles and terrain in his path but eventually entered an area of level-three (now referred to as “heavy”) precipitation associated with a building thunderstorm. The pilot was killed when he lost control of the airplane and plunged into the marshy terrain.
Watch a narrated flight sim animation of the accident sequence.
The Cherokee pilot intended to fly from Bismarck Municipal Airport in Bismarck, N.D., to Fergus Falls Municipal Airport in Fergus Falls, Minn. Instrument meteorological conditions and scattered thunderstorms were forecast along the 190-mile route, but the VFR-only pilot did not request any weather briefing services prior to or during the flight, and no flight plan was filed.
The pilot contacted Bismarck ground control at 11:20 a.m., requested an eastbound departure, and was cleared to taxi to Runway 13. At the time, the airport’s automated weather system was reporting an overcast ceiling at 1,000 feet, with a thunderstorm approaching from the north.
At 11:23 a.m., the Cherokee pilot was cleared for takeoff and told to proceed on course toward Fergus Falls. Three minutes after departure, the pilot acknowledged a clearance to change radio frequency. No further communications were received from the aircraft.
Over the next hour, the Cherokee proceeded east-southeast as weather conditions deteriorated. Rain and mist reduced the visibility to five miles, and the ceiling dropped to 500 feet. Temperature and dew point were converging. As conditions worsened, the airplane flew lower and lower, cruising a mere 200 feet above the ground.
At 12:32 p.m., radar returns showed the aircraft approximately three to five miles northwest of a level-three thunderstorm. Data indicated the convective cell was producing moderate turbulence and intensifying in strength. With its pilot struggling to maintain control, the Cherokee continued directly toward the storm for another mile and a half before finally disappearing from radar.
Six weeks passed before the wreckage was discovered in a rain-swollen bog 10 miles northwest of Kulm, N.D. The NTSB determined that the accident’s probable cause was the noninstrument-rated pilot’s continued flight into instrument meteorological conditions, which resulted in his inadvertent encounter with a thunderstorm and subsequent loss of aircraft control.
Heavy thunderstorms can produce strong turbulence, lightning, hail, and surface wind gusts. They can also cause powerful downdrafts and dangerous vertical and horizontal wind shear. An aircraft flying at 200 feet agl—as the accident Cherokee was—could be quickly thrust into terrain if it encountered strong downward forces or airspeed-robbing wind shear. Indeed, even moderate turbulence could prove deadly with such a small margin of safety.
This accident also illustrates the importance of filing a VFR flight plan. The wreckage from this August crash wasn’t discovered until early October, in part because searchers weren’t exactly sure where to look. Filing and activating a VFR flight plan ensures a timely search-and-rescue response. If you end up trapped in a wrecked airplane—or even down in a remote area without cell phone reception following a precautionary landing—a quick and accurate search could make all the difference.