Aircraft Accident/Incident Report

Oso, Washington 98223
Monday, August 10, 1998 10:05 PDT

NTSB Narrative Summary Released at Completion of Accident

At about 250 feet above the ground, the pilot-in-command heard a bang and saw the tail rotor gear box fly past the rotorcraft on the left side. The rotorcraft then 'nosed over and started turning to the right at a fast rate of speed.' The pilot-in-command then entered an autorotation and the rotorcraft impacted the ground. The tail rotor gearbox, tail rotor output shaft, fork assembly, swash-plate with pitch links, tail-boom aft fitting, and tail rotor driveshaft flex-coupling were recovered. Those items were inspected and tested at Boeing Helicopters, Mesa. The fracture mode for all of the components evaluated was ductile overload. The output shaft exhibited severe bending displacement of approximately 0.925 inches relative to a theoretical line along the centerline, characteristic of a brief, unbalanced load. The conical bearing surfaces of the tail rotor fork assembly were examined and determined to be void of heavy or unusual wear patterns. The tail rotor blades were not found during the course of the investigation.

NTSB Probable Cause Narrative

The separation of the 90 degree gearbox and tail rotor assembly for undetermined reasons followed by the inability of the pilot-in-command to maintain control of the rotorcraft.

Event Information

Type of Event Accident
Event Date 8/10/1998
Event Day of the Week Monday
Time of Event 1005
Event Time Zone Pacific Daylight Time
Event City OSO
Event State WASHINGTON
Event Country --
Zipcode of the event site 98223
Event Date Year 1998
Event Date Month 8
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 955 Pacific Daylight Time
Direction of event from weather observation facility (degrees) 185
Weather Observation Facility ID AWO
Elevation of weather observation facility 37
Distance of event from weather observation facility (units?) 8
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 Unknown
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) 19
Dew Point at event time (in degress fahrenheit) 13
Wind Direction (degrees magnetic) 180
Variable Wind Indicator Unknown
Wind Speed (knots) 3
Wind Velocity Indicator Unknown
Wind Gust Indicator Not Gusting
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 Minor
On Ground, Fatal Injuries 0
On Ground, Minor Injuries 0
On Ground, Serious Injuries 0
Injury Total Fatal --
Injury Total Minor 1
Injury Total None --
Injury Total Serious --
Injury Total All 1
Investigating Agency NTSB
NTSB Docket Number (internal use) 1265
NTSB Notification Source --
NTSB Notification Date Aug 10 1998 12:00AM
NTSB Notification Time 1026
Fiche Number and/or location -used to find docket information IMAGE
Date of most recent change to record Dec 11 2000 11:43AM
User who most recently changed record dbo
Basic weather conditions Visual Meteorological Cond
FAA District Office --

Aircraft Involved

Aircraft #1

Aircraft Registration Number N1096L
NTSB Number SEA98LA160
Missing Aircraft Indicator N
Federal Aviation Reg. Part Part 133: Rotorcraft Ext. Load
Type of Flight Plan filed None
Flight plan Was Activated? --
Damage Substantial
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name McDonnell Douglas
Aircraft Model 369D
Aircraft Series Identifier 369D
Aircraft Serial Number 800789D
Certified Max Gross Weight 3000
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 4
Number of Engines 1
Fixed gear or retractable gear Fixed
Aircraft, Type of Last Inspection Continuous Airworthiness
Date of Last Inspection Aug 28 1998 12:00AM
Airframe hours since last inspection 24
Airframe Hours 5499
ELT Installed Yes
ELT Activated Yes
ELT Aided Location of Event Site No
ELT Type --
Aircraft Owner Name EAGLE AIR HELICOPTERS, INC.
Aircraft Owner Street Address PO BOX 1555
Aircraft Owner City FORKS
Aircraft Owner State WA
Aircraft Owner Country
Aircraft Owner Zipcode 98331
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 GHHL
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 No
Departure Airport Code AWO
Departure City ARLINGTON
Departure State WA
Departure Country
Departure Time 745
Departure Time Zone PDT
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 Jan 2 2001 10:34AM
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 --