# NTSB SEA95LA078: Bell UH-1B, N39SD, Walla Walla, WA, April 22, 1995 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: April 22, 1995, 09:50 local (16:50 UTC) - Place: Walla Walla, WA - Coordinates: 46.109668, -118.300659 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.1097&lon=-118.3007&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report August 23, 1995 - Report: Approved by Office Director - NTSB case key (mKey): 42134 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA95LA078 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/42134/pdf - Page: https://openairdocs.org/ntsb/SEA95LA078 ## Probable cause TOTAL FAILURE OF THE FREEWHEELING SPRAG UNIT. A FACTOR TO THE ACCIDENT WAS: SUITABLE TERRAIN WAS NOT AVAILABLE FOR LANDING. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - rotor drive system,freewheeling sprag unit - failure,total (cause) - Forced landing, emergency descent/landing - In flight collision with object, emergency descent/landing - terrain condition - none suitable (contributing factor) - object - tree(s) ## Analysis THE PILOT STATED THAT DURING AN EXTERNAL LOAD OPERATION, JUST AFTER THE LOAD CLEARED THE GROUND THE HELICOPTER SHUTTERED AND MADE A LOUD SCRAPING NOISE FOLLOWED BY LOW ROTOR RPM. THE PILOT RELEASED THE LOAD AND MANEUVERED FOR AN EMERGENCY LANDING. DURING THE MANEUVER, THE HELICOPTER COLLIDED WITH TREES. DURING THE POST CRASH INSPECTION, IT WAS FOUND THAT THE FREEWHEELING ONE-WAY CLUTCH ASSEMBLY HAD FAILED IN FLIGHT. THE CLUTCH ASSEMBLY APPEARED TO BE WORN AND THE INNER CLUTCH RACE DISPLAYED SIGNS OF BRINELLING. ## Factual narrative On April 22, 1995, approximately 0950 Pacific daylight time, a Bell UH-1B, N39SD, experienced a loss of engine power during an external load operation and collided with trees on steep mountainous terrain approximately 10 miles southeast of Walla Walla, Washington. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was substantially damaged and the commercial pilot, the sole occupant, was seriously injured. The flight originated from a remote job site and was operating in the local area. The president of Blue Mountain Helicopters reported that during the external load operation, the flight was at the mid point of the one hour cycle. The pilot positioned the helicopter for a turn of logs. The ground crew hooked the load and the pilot started up with the load. The crew reported that the logs had just cleared the ground when the load was released. The crew stated that the helicopter's engine "immediately got quiet and the blades began getting slower." The pilot released the long line and nosed the helicopter down hill. The helicopter travelled approximately 300 feet before colliding with trees. The pilot reported that he was in a hover over the load and had just picked it off the ground when the helicopter "shuddered and made a loud scraping noise like that of a chain hoist slipping." The pilot noticed a low rotor rpm and he immediately bottomed the collective to maintain rotor rpm. The helicopter yawed slightly to the right and the pilot guided the helicopter to an opening in the trees and pulled full collective to stop before colliding with the trees. The operator reported that the long line was 150 feet in length. The load weighed approximately 2,400 pounds and consisted of two logs measuring 16 feet and 22 feet. During the engine and airframe inspection, it was found that the freewheeling one-way clutch assembly failed in flight when the sprags rolled over and portions of sprags were ground off by the clutch races. This failure resulted in the loss of engine power that was transmitted to the main rotor transmission. The one-way clutch appeared to be worn. The inner clutch race displayed signs of brinelling. ## Aircraft - Registration: N39SD (not matched to a registry record) - Reported make and model: BELL UH-1B - Category: Helicopter - Serial number: 63-8699 - Airframe hours: 4810 - Engines: LYCOMING T53-L13B-22 1250 horsepower turbo shaft - Damage: Substantial damage - Flight: Other work use, Part 133 - Registered owner: Blue Mountain Helicopter Inc. - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, April 8, 1995, 34 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 44; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 20,733 total, 2,297 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 30 statute miles - Lowest ceiling: none - Temperature: 50 °F ## 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 19950422042719A](https://openairdocs.org/incident/19950422042719A), Apr 22, 1995: Bell UH1B, Walla Walla, WA, Substantial damage. Dropped logs right after lifting. Had lost power to rotors. Hit trees trying to land. Free wheeling clutch failed. 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.