Aircraft Accident/Incident Report

Antelope Island, Utah 84075
Tuesady, March 3, 2009 8:40 MST

NTSB Narrative Summary Released at Completion of Accident

Radar data and a performance study depicted the airplane flying on a steady northerly course adjacent to mountains at 113 knots calibrated airspeed. The pilot changed course slightly to fly close to or over the mountains. The airplane subsequently experienced an in-flight breakup. All of the airplane's structural components and flight control surfaces were located at the main impact site. There was no evidence of excessive airspeed or maneuvers that would lead to a structural overload and failure of the wings. Turbulence was present in the area, although it was not believed to be severe and likely did not contribute to the failure. An examination of the airplane wreckage revealed that the left wing spar had buckled upward near the fuselage and the left wing had wrapped around the fuselage near the cockpit. There was compression buckling of the lower spar cap of the left wing's rear spar and compression buckling of the upper and lower spar caps of the right wing's rear spar. The compression damage to both rear spars and the upward buckling of the left wing's main spar are evidence of upward and downward bending of both wings. The upward and downward bending of the wings is consistent with aerodynamic flutter. The structural loading at the inboard section of the left wing was further increased as the trailing edges of the outboard sections moved up and down. Ultimately the left wing failed as it bent upward near the root. Aerodynamic flutter can occur when there is insufficient stiffness in the structure or when the flight controls are not mass-balanced. Counterbalanced flight controls can protect less stiff surfaces at higher airspeeds. The ailerons did not have counterbalances, which would have offered direct protection from aerodynamic flutter.

NTSB Probable Cause Narrative

The in-flight failure of both wings due to aileron flutter. The aileron flutter was the result of inadequate wing stiffness and the lack of aileron counterbalances.

Event Information

Type of Event Accident
Event Date 3/3/2009
Event Day of the Week Tuesday
Time of Event 840
Event Time Zone Mountain Standard Time
Event City Antelope Island
Event State UTAH
Event Country --
Zipcode of the event site 84075
Event Date Year 2009
Event Date Month 3
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude 405733N
Event Location Longitude 1121349W
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 --
Investigator's weather source Weather Observation Facility
Time of the weather observation 853 Mountain Standard Time
Direction of event from weather observation facility (degrees) 140
Weather Observation Facility ID KSLC
Elevation of weather observation facility 4220
Distance of event from weather observation facility (units?) 17
Time Zone of the weather observation MST
Lighting Conditions Day
Lowest Ceiling Height 20000
Lowest Non-Ceiling Height 7000
Sky/Lowest/Cloud Conditions Few
Sky Condition for Lowest Ceiling Broken
Visibility Runway Visual Range (Feet) --
Visibility Runway Visual Value (Statute Miles) --
Visibility (Statute Miles) 10
Air Temperature at event time (in degrees celsius) 13
Dew Point at event time (in degress fahrenheit) 0
Wind Direction (degrees magnetic) 160
Variable Wind Indicator Wind direction could be determined
Wind Speed (knots) 17
Wind Velocity Indicator --
Wind Gust Indicator --
Wind Gust (knots) --
Altimeter Setting at event time (in. Hg) 29.93
Density Altitude (feet) --
Intensity of Precipitation --
METAR weather report --
Event Highest Injury Fatal
On Ground, Fatal Injuries --
On Ground, Minor Injuries --
On Ground, Serious Injuries --
Injury Total Fatal 1
Injury Total Minor --
Injury Total None --
Injury Total Serious --
Injury Total All 1
Investigating Agency NTSB
NTSB Docket Number (internal use) 26593
NTSB Notification Source FAA SEA ROC
NTSB Notification Date --
NTSB Notification Time --
Fiche Number and/or location -used to find docket information --
Date of most recent change to record Oct 6 2011 9:09PM
User who most recently changed record stam
Basic weather conditions Visual Meteorological Cond
FAA District Office --

Aircraft Involved

Aircraft #1

Aircraft Registration Number N3683X
NTSB Number WPR09FA141
Missing Aircraft Indicator --
Federal Aviation Reg. Part Part 91: General Aviation
Type of Flight Plan filed None
Flight plan Was Activated? No
Damage Substantial
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name STEPHENSON
Aircraft Model ZODIAC 601 XL
Aircraft Series Identifier --
Aircraft Serial Number 6-5136
Certified Max Gross Weight --
Aircraft Category Airplane
Aircraft Registration Class --
Aircraft is a homebuilt? Yes
Flight Crew Seats 1
Cabin Crew Seats --
Passenger Seats 1
Total number of seats on the aircraft 2
Number of Engines 1
Fixed gear or retractable gear Fixed
Aircraft, Type of Last Inspection Conditional
Date of Last Inspection Nov 11 2008 12:00AM
Airframe hours since last inspection --
Airframe Hours 14
ELT Installed Yes
ELT Activated Yes
ELT Aided Location of Event Site No
ELT Type C91
Aircraft Owner Name DENNIS STEPHENSON
Aircraft Owner Street Address --
Aircraft Owner City MIDVALE
Aircraft Owner State UT
Aircraft Owner Country USA
Aircraft Owner Zipcode 84047-2132
Operator is an individual? No
Operator Name Kirk Babbitt
Operator Same as Owner? No
Operator Is Doing Business As --
Operator Address Same as Owner? No
Operator Street Address --
Operator City Stansbury Park
Operator State UT
Operator Country USA
Operator Zip code 84074
Operator Code --
Owner has at least one certificate None
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation --
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not --
Indicates Domestic or International Flight --
Operator carrying Pax/Cargo/Mail --
Type of Flying (Per_Bus / Primary) Personal
Second Pilot on Board No
Departure Point Same as Event No
Departure Airport Code KTVY
Departure City Tooele
Departure State UT
Departure Country USA
Departure Time 818
Departure Time Zone MST
Destination Same as Local Flt --
Destination Airport Code BTF
Destination City Bountiful
Destination State UT
Destination Country USA
Specific Phase of Flight --
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record Oct 6 2011 8:39PM
User who most recently changed record stam
Since inspection or accident Time of Accident
Event Location Runway Number and Location N/A
Runway Length --
Runway Width --
Sight Seeing flight No
Air Medical Flight No
Medical Flight --