# NTSB WPR17LA145: Piper L 21B, N99031, Big Timber, MT, July 8, 2017 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: July 8, 2017, 10:45 local (16:45 UTC) - Place: Big Timber, MT - Coordinates: 45.841945, -109.894165 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=45.8419&lon=-109.8942&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Loss of control in flight](https://openairdocs.org/ntsb-events/240) - Highest injury: Serious injuries - Injuries: 2 serious - Status: Completed, report November 14, 2017 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 95525 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA145 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95525/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95525 - Page: https://openairdocs.org/ntsb/WPR17LA145 ## Probable cause The pilot's decision to fly at low altitude in the vicinity of power lines, which resulted in a wire strike. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Info processing/decision: decision making/judgment](https://openairdocs.org/ntsb-findings/02041520): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [All aircraft, 3,098 cases](https://openairdocs.org/ntsb-findings/02041520/cases.md) - [Attention/monitoring: monitoring environment](https://openairdocs.org/ntsb-findings/02021545): Personnel issues › Psychological · Pilot (probable cause); cases with it: [All aircraft, 809 cases](https://openairdocs.org/ntsb-findings/02021545/cases.md) - [Performance/control parameters: altitude](https://openairdocs.org/ntsb-findings/01062012): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [All aircraft, 1,310 cases](https://openairdocs.org/ntsb-findings/01062012/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-low-alt flying: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) - [Maneuvering-low-alt flying: Loss of control in flight](https://openairdocs.org/ntsb-events/240) (defining event); cases with it: [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) - [Uncontrolled descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis 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. ## Factual narrative On July 8, 2017, about 1045 mountain daylight time, a Piper L-21B, N99031, was substantially damaged during a wire strike and subsequent impact with the Yellowstone River in Big Timber, Montana. The private pilot and his passenger were seriously injured. The airplane was owned by a private individual and operated by the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed and no flight plan was filed for the local flight. The flight departed Big Timber Airport (6S0), Big Timber, Montana about 1030. According to the pilot, he departed the airport to the north with a family member onboard. The pilot then turned east to follow the river and look for his sister who was participating in a water sport. The airplane was about at tree level when it collided with a set of power lines and then immediately impacted the water. The pilot reported to his father that he observed sparks and wires before the airplane entered a nose-down dive. The 1055 recorded weather observation at 6S0 included wind 220° true at 11 knots, visibility 10 statute miles, clear skies, temperature 25° C, dew point 11° C, and an altimeter setting of 30.20 inches of mercury. According to the U.S. Naval Observatory, the sun azimuth at the time of the accident would have been 116°. The airplane came to rest near an eyot approximately 4 nm northeast of 6S0. Photographs from the Federal Aviation Administration revealed that the airplane sustained substantial damage to the wings, empennage, and fuselage. The pilot reported that the airplane was on a southeast course at the time of the accident. He noted that the sun was on the horizon, but did not obstruct his vision. The pilot further remarked that he was aware of the presence of these power lines from a previous experience flying over the Yellowstone River, several years ago. A law enforcement representative stated that he observed a broken residential power line near the accident site and that he received reports of a disruption in power service from nearby residents around the time of the accident. The silver colored power line was one of a three phase power configuration that ran between two distribution towers on both sides of the river from a height of approximately 90 feet. The towers were about 4 nm east of the airport. According to the pilot's father, who is also the 6S0 airport manager, transient pilots frequently fly at low altitudes over this particular portion of the Yellowstone River to avoid turbulent air in the summertime. The airport manager further reported that the power lines were not equipped with aerial marker balls for identification. At the request of the NTSB Investigator-in-Charge, the airport manager agreed to install signage in the local fixed based operator office at 6S0 to caution pilots of the presence of power lines over the Yellowstone River. ## Aircraft - Registration: N99031 (not matched to a registry record) - Reported make and model: PIPER L 21B (B) - Category: Airplane - Serial number: 54-2590 - Year built: 1954 - Airframe hours: 2557.2 - Engines: Lycoming O-320-A2B 160 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 28, 2017, 0 hours before - Departed: 6S0, BIG TIMBER, MT - Destination: 6S0, BIG TIMBER, MT - Equipment: Handheld GPS ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; injuries: serious; private; airplane ratings: single-engine land; medical: class 3, with waivers/limitations; seat: front; restraint: 3-point; flight hours: 600 total, 180 in this make and model, 585 as pilot in command, 2 in the last 90 days ## Weather - Conditions: Visual (VMC), Day - Wind: 220° at 11 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 77 °F, dew point 52 °F - Altimeter: 30.20 inHg - Observed at: 6S0, 4 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20170708007979A](https://openairdocs.org/incident/20170708007979A), Jul 8, 2017: Piper L-21B, Big Timber, MT, Destroyed. Aircraft departed the Big Timber airport (6S0) headed eastward along the yellowstone river at a low altitude. Aircraft struck power lines traversing the river… ## Docket (5 files) The files NTSB released with the investigation on September 1, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95525. 2.6 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40455847&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Record of Conversations (item 2, .PDF, 94 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40455848&FileExtension=.PDF&FileName=Record%20of%20Conversations-Master.PDF - Weather Report and Records (item 3, .PDF, 109 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40455849&FileExtension=.PDF&FileName=Weather%20Report%20and%20Records-Master.PDF - Sun Azimuth, U.S. Naval Observatory (item 4, .PDF, 52 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40455850&FileExtension=.PDF&FileName=Sun%20Azimuth,%20U.S.%20Naval%20Observatory-Master.PDF - Accident Photographs (item 5, .PDF, 669 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40455851&FileExtension=.PDF&FileName=Accident%20Photographs-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.