# NTSB SEA93LA213: Bell UH-1B, N70NW, Detroit Lake, OR, September 24, 1993 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: September 24, 1993, 10:50 local (17:50 UTC) - Place: Detroit Lake, OR - Coordinates: 44.739395, -121.88095 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=44.7394&lon=-121.8809&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report September 13, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 41779 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA93LA213 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41779/pdf - Page: https://openairdocs.org/ntsb/SEA93LA213 ## Probable cause FAILURE OF A SECOND STAGE TURBINE WHEEL TOO LOW FOR A SUCCESSFUL AUTOROTATION. FACTORS INCLUDE A TREE IN THE APPROACH PATH. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, approach - turboshaft engine,free(power) turbine - fatigue (cause) - Forced landing, descent - emergency - In flight collision with object, descent - uncontrolled - object - tree(s) (contributing factor) ## Analysis THE AIRCRAFT STRUCK TREES WHILE ATTEMPTING AN AUTOROTATION AFTER AN ENGINE FAILURE. THE PILOT HAD PUNCHED OFF HIS EXTERNAL LOAD AFTER THE POWER LOSS, BUT WAS UNABLE TO SUCCESSFULLY ACCOMPLISH THE AUTOROTATION DUE TO INSUFFICIENT ALTITUDE AND UNSUITABLE TERRAIN. THE ENGINE FAILURE WAS THE RESULT OF THE FATIGUE FRACTURE OF BLADE NUMBER 19 OF THE SECOND STAGE TURBINE ROTOR ASSEMBLY. ## Factual narrative On September 24, 1993, at approximately 0930 Pacific daylight time, a Bell UH-1B, N70NW, sustained substantial damage when it collided with terrain after an apparent loss of engine power, while engaged in aerial logging operations. The commercial pilot, who was the sole occupant of the aircraft, was seriously injured. Visual meteorological conditions prevailed at the time of the accident. The pilot reported that he was approaching the drop pad at between 200 and 250 feet above ground level with a 3000 pound load on a 150 foot long line. In a telephone conversation, he stated that he heard a high pitch sound, the rotor low rpm light illuminated, and he noted a loss of power. He said he punched the load, told the crew to clear the area, and initiated an autorotation to the pad. In his written statement, he noted that he heard a loud screeching, grinding noise when he lost power. he said that he intended to set down on the landing (pad) and made a radio call to clear the landing of landing crew. As there were longs on the landing, he decided to set down on the road a couple hundred feet away. The aircraft struck a tree during the descent and landed hard. The engine was disassembled for inspection. The second stage turbine rotor assembly, P/N P1-140-205-06Y was removed and shipped to the NTSB materials laboratory for inspection and testing. Visual examination of the turbine disk noted that ten of the 62 blades were broken through the airfoil section. Two of the ten were fractured close to the blade platforms near the disk rim. Additionally, the forward bearing shaft of the rotor was separated near the rotor disc. The metallurgist's report is attached separately. ## Aircraft - Registration: N70NW (not matched to a registry record) - Reported make and model: BELL UH-1B - Category: Helicopter - Serial number: 60-3568 - Airframe hours: 4465 - Engines: LYCOMING T53-L-11D turbo shaft - Damage: Substantial damage - Flight: Other work use, Part 137 - Operator: Northwest Helicopters, Inc - Registered owner: Northwest Helicopters, Inc - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, September 13, 1993, 47 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 44; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 6,800 total, 1,241 in this make and model, 6,200 as pilot in command, 50 in the last 90 days, 50 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Visibility: 25 statute miles - Lowest ceiling: none - Temperature: 63 °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 19930924036309A](https://openairdocs.org/incident/19930924036309A), Sep 24, 1993: Bell UH1B, Detroit Lake, OR, Substantial damage. Loud noise. Dropped logs made autorotation. Struck tree. Ten blades broke on airfoil section turbine. Bearing also. 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.