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Aviation Accident

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NTSB Identification: WPR17LA145
14 CFR Part 91: General Aviation
Accident occurred Saturday, July 08, 2017 in Big Timber, MT
Probable Cause Approval Date: 11/14/2017
Aircraft: PIPER L 21B, registration: N99031
Injuries: 2 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The private pilot reported that, after departure, he followed the course of a river at an altitude about level with the treetops. Although the pilot was aware of powerlines in the area, he did not see them before the airplane collided with the powerlines about 90 ft above ground level. The airplane subsequently nosed down and impacted the river, resulting in substantial damage.
According to the manager of the airport from which the airplane departed, it is not uncommon for pilots to fly at low altitudes in that area to avoid turbulent air in the summertime. He further reported that the power lines were not equipped with aerial marker balls. Following the accident, the airport manager agreed to install signage in the fixed base operator at the airport to caution pilots of the presence of power lines in that area.


The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
  • The pilot's decision to fly at low altitude in the vicinity of power lines, which resulted in a wire strike.