Aircraft Incident/Accident Report


Mammoth Lakes, California 93546
Sunday, April 29, 1990 7:10 PDT

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NTSB Narrative Summary Released at Completion of Accident
THE PILOT ENCOUNTERED A STRONG DOWNDRAFT WHILE CRUISING AT 250 TO 300 FEET AGL. HE LOST CONTROL OF THE HELICOPTER, WAS UNABLE TO ARREST THE DESCENT, AND COLLIDED WITH 7000 MSL TERRAIN.
NTSB Probable Cause Narrative
PILOT'S ENCOUNTER WITH A STRONG DOWNDRAFT WHILE CRUISING AT AN INADEQUATE ALTITUDE. A CONTRIBUTING FACTOR WAS THE HIGH ALTITUDE WHICH LIMITED AVAILABLE ENGINE POWER FOR RECOVERY.
Event Information
Type of EventAccident 
Event Date4/29/1990 
Event Day of the WeekSunday 
Time of Event710 
Event Time ZonePacific Daylight Time 
Event CityMAMMOTH LAKES  
Event StateCALIFORNIA 
Event Country-- 
Zipcode of the event site93546  
Event Date Year1990 
Event Date Month
MidAir Collision IndicatorNo 
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 airportOff Airport/Airstrip 
Distance from airport in statute miles
Degrees magnetic from airport
Airport Elevation
Weather Briefing CompletenessUnknown 
Investigator's weather sourcePilot 
Time of the weather observation710  
Direction of event from weather observation facility (degrees)
Weather Observation Facility ID  
Elevation of weather observation facility
Distance of event from weather observation facility (units?)
Time Zone of the weather observation  
Lighting ConditionsDay 
Lowest Ceiling Height
Lowest Non-Ceiling Height
Sky/Lowest/Cloud ConditionsClear 
Sky Condition for Lowest CeilingNone 
Visibility Runway Visual Range (Feet)
Visibility Runway Visual Value (Statute Miles)
Visibility (Statute Miles) 50 
Air Temperature at event time (in degrees celsius)-- 
Dew Point at event time (in degress fahrenheit)-18 
Wind Direction (degrees magnetic)
Variable Wind IndicatorUnknown 
Wind Speed (knots)
Wind Velocity Indicator Unknown 
Wind Gust IndicatorNot Gusting 
Wind Gust (knots)
Altimeter Setting at event time (in. Hg) -- 
Density Altitude (feet)
Intensity of PrecipitationUnknown 
METAR weather report -- 
Event Highest InjuryMinor 
On Ground, Fatal Injuries
On Ground, Minor Injuries
On Ground, Serious Injuries
Injury Total Fatal-- 
Injury Total Minor
Injury Total None-- 
Injury Total Serious-- 
Injury Total All
Investigating AgencyNTSB 
NTSB Docket Number (internal use)1223 
NTSB Notification Source-- 
NTSB Notification DateApr 29 1990 12:00AM 
NTSB Notification Time1000 
Fiche Number and/or location -used to find docket information42585 
Date of most recent change to recordDec 18 2002 11:28AM 
User who most recently changed recordNTSB\GIUV  
Basic weather conditionsVisual Meteorological Cond 
FAA District Office-- 
Aircraft Involved
Aircraft #1
Aircraft Registration NumberN8560M 
NTSB NumberLAX90LA157  
Missing Aircraft Indicator
Federal Aviation Reg. PartPart 91: General Aviation 
Type of Flight Plan filedNone 
Flight plan Was Activated?-- 
DamageSubstantial 
Aircraft FireNone 
Aircraft ExplosionNone 
Aircraft Manufacturer's Full NameROBINSON  
Aircraft ModelR22  
Aircraft Series IdentifierR22  
Aircraft Serial Number0476  
Certified Max Gross Weight1370 
Aircraft CategoryHelicopter 
Aircraft Registration ClassU.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
Number of Engines
Fixed gear or retractable gearRetractable 
Aircraft, Type of Last InspectionUnknown 
Date of Last Inspection-- 
Airframe hours since last inspection
Airframe Hours-- 
ELT InstalledUnknown 
ELT ActivatedUnknown 
ELT Aided Location of Event SiteUnknown 
ELT Type-- 
Aircraft Owner NameLOUIS W. THACKER  
Aircraft Owner Street Address465 JUNIPER ST.  
Aircraft Owner CityCHICO  
Aircraft Owner StateCA 
Aircraft Owner Country  
Aircraft Owner Zipcode95926  
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  
Owner has at least one certificateNone 
Other Operator of large aircraft?No 
Certified for Part 133 or 137 OperationUnknown 
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 BoardNo 
Departure Point Same as EventNo 
Departure Airport CodeB1H  
Departure CityBISHOP  
Departure StateCA 
Departure Country  
Departure Time628 
Departure Time ZonePDT 
Destination Same as Local Flt-- 
Destination Airport CodeMEV  
Destination CityMINDEN  
Destination StateNV 
Destination Country  
Specific Phase of FlightDescent 
Report sent to ICAO?-- 
Evacuation occurred-- 
Date of most recent change to recordJan 2 2001 10:35AM 
User who most recently changed recorddbo  
Since inspection or accident-- 
Event Location Runway Number and Location0  
Runway Length
Runway Width
Sight Seeing flightNo 
Air Medical FlightNo 
Medical Flight--