Aircraft Accident/Incident Report

Usk, Washington 99180
Tuesady, September 21, 1999 14:05 PDT

NTSB Narrative Summary Released at Completion of Accident

The lower surface of the 90-degree gearbox exhibited fracture surfaces of the six attachment studs. Fretting was observed on the lower surface where the gearbox quill assembly was attached. The fracture surfaces for the six attachment studs each showed one or two relatively flat regions with smooth curving boundaries typical of fatigue. Multiple origin sites were identified on each stud, with observed ratchet marks. All of the origin areas were circumferentially aligned with the center of the gearbox, with origins on both sides of each stud, except for one stud, which had an origin area on only one side. In each case, the larger fatigue region had origins on the counter-clockwise side of the stud (as viewed from above, from the center of the gearbox).

NTSB Probable Cause Narrative

Fatigue failure of the 90-degree gearbox attachment studs, resulting in separation of the tailrotor and 90-degree gearbox from the vertical fin.

Event Information

Type of Event Accident
Event Date 9/21/1999
Event Day of the Week Tuesday
Time of Event 1405
Event Time Zone Pacific Daylight Time
Event City USK
Event State WASHINGTON
Event Country --
Zipcode of the event site 99180
Event Date Year 1999
Event Date Month 9
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude --
Event Location Longitude --
Event Location Airport
Event Location Nearest Airport ID
Indicates whether the acc/inc occurred off or on an airport Off Airport/Airstrip
Distance from airport in statute miles --
Degrees magnetic from airport --
Airport Elevation --
Weather Briefing Completeness Unknown
Investigator's weather source Weather Observation Facility
Time of the weather observation 1356 Pacific Daylight Time
Direction of event from weather observation facility (degrees) 0
Weather Observation Facility ID KGE
Elevation of weather observation facility 0
Distance of event from weather observation facility (units?) 0
Time Zone of the weather observation PDT
Lighting Conditions Day
Lowest Ceiling Height 0
Lowest Non-Ceiling Height 0
Sky/Lowest/Cloud Conditions Clear
Sky Condition for Lowest Ceiling None
Visibility Runway Visual Range (Feet) 0
Visibility Runway Visual Value (Statute Miles) 0
Visibility (Statute Miles) 10
Air Temperature at event time (in degrees celsius) 28
Dew Point at event time (in degress fahrenheit) 4
Wind Direction (degrees magnetic) 30
Variable Wind Indicator Unknown
Wind Speed (knots) 6
Wind Velocity Indicator Unknown
Wind Gust Indicator Unknown
Wind Gust (knots) 0
Altimeter Setting at event time (in. Hg) 30
Density Altitude (feet) --
Intensity of Precipitation Unknown
METAR weather report --
Event Highest Injury None
On Ground, Fatal Injuries 0
On Ground, Minor Injuries 0
On Ground, Serious Injuries 0
Injury Total Fatal --
Injury Total Minor --
Injury Total None 1
Injury Total Serious --
Injury Total All --
Investigating Agency NTSB
NTSB Docket Number (internal use) 1908
NTSB Notification Source --
NTSB Notification Date Sep 21 1999 12:00AM
NTSB Notification Time 1511
Fiche Number and/or location -used to find docket information IMAGE
Date of most recent change to record May 11 2001 4:06AM
User who most recently changed record dbo
Basic weather conditions Visual Meteorological Cond
FAA District Office --

Aircraft Involved

Aircraft #1

Aircraft Registration Number N32800
NTSB Number SEA99LA171
Missing Aircraft Indicator N
Federal Aviation Reg. Part Part 133: Rotorcraft Ext. Load
Type of Flight Plan filed Unknown
Flight plan Was Activated? --
Damage Substantial
Aircraft Fire Ground
Aircraft Explosion None
Aircraft Manufacturer's Full Name Garlick
Aircraft Model UH-1H
Aircraft Series Identifier UH-1H
Aircraft Serial Number 6616854
Certified Max Gross Weight 9500
Aircraft Category Helicopter
Aircraft Registration Class U.S. Registered/U.S. Soil
Aircraft is a homebuilt? No
Flight Crew Seats --
Cabin Crew Seats --
Passenger Seats --
Total number of seats on the aircraft 2
Number of Engines 1
Fixed gear or retractable gear Fixed
Aircraft, Type of Last Inspection Unknown
Date of Last Inspection Sep 9 1999 12:00AM
Airframe hours since last inspection 50
Airframe Hours 12230
ELT Installed No
ELT Activated Unknown
ELT Aided Location of Event Site Unknown
ELT Type --
Aircraft Owner Name BLUE MOUNTAIN HELICOPTERS, INC
Aircraft Owner Street Address 1820 S MAIN
Aircraft Owner City MILTON-FREEWTR
Aircraft Owner State OR
Aircraft Owner Country
Aircraft Owner Zipcode 97862
Operator is an individual? --
Operator Name
Operator Same as Owner? Yes
Operator Is Doing Business As --
Operator Address Same as Owner? Yes
Operator Street Address
Operator City
Operator State
Operator Country
Operator Zip code
Operator Code GASL
Owner has at least one certificate Yes - certificate holder
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation External Load
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not Unknown
Indicates Domestic or International Flight Unknown
Operator carrying Pax/Cargo/Mail Unknown
Type of Flying (Per_Bus / Primary) Other Work Use
Second Pilot on Board No
Departure Point Same as Event Yes
Departure Airport Code
Departure City
Departure State
Departure Country
Departure Time 0
Departure Time Zone
Destination Same as Local Flt dest & departure same, accident can occur anywhere
Destination Airport Code
Destination City
Destination State
Destination Country
Specific Phase of Flight --
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record May 11 2001 4:06AM
User who most recently changed record dbo
Since inspection or accident --
Event Location Runway Number and Location 0
Runway Length --
Runway Width --
Sight Seeing flight No
Air Medical Flight No
Medical Flight --