# NTSB LAX91LA375: Beierle Thunder Gull J, Santa Margarita, CA, August 24, 1991

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Limited investigation · Final report
- Date: August 24, 1991, 11:25 local (18:25 UTC)
- Place: Santa Margarita, CA
- Coordinates: 35.309906, -120.270149 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=35.3099&lon=-120.2701&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious, 1 minor
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 27343
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA375
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27343/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA375

## Probable cause

THE FAILURE OF THE WING SPAR WHEN THE DESIGN LIMITS OF THE AIRPLANE WAS EXCEEDED BY THE PILOT. CONTRIBUTING TO THE ACCIDENT WAS AN INADEQUATE AIRFRAME DESIGN AND AN ABRUPT MOVEMENT OF THE FLIGHT CONTROLS BY THE PILOT.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, maneuvering
  - wing,spar - buckled (cause)
  - flight controls - abrupt, pilot in command (contributing factor)
  - design stress limits of aircraft - exceeded, pilot in command (cause)
  - acft/equip,inadequate airframe, pilot in command (contributing factor)
- Loss of control - in flight, descent - uncontrolled
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - ground

## Analysis

THE CERTIFICATED PRIVATE PILOT AND A PASSENGER WERE CONDUCTING A FLIGHT TEST OF AN UNREGISTERED, HOMEBUILT AIRPLANE. THE AIRPLANE WAS BEING MARKETED AS AN ULTRALIGHT VEHICLE WITH AN EXCEPTION OF THE ULTRALIGHT REGULATIONS GRANTED TO THE EXPERIMENTAL AIRCRAFT ASSOCIATION. THE PILOT WAS PERFORMING AEROBATIC MANEUVERS WHILE THE PASSENGER WAS FILMING THE EVENT FROM THE REAR SEAT. DURING THE PULL-UP PORTION OF AN IMMELMAN MANEUVER, THE LEFT WING FAILED AND FOLDED UPWARDS. THE PILOT DEPLOYED A BALLISTIC PARACHUTE TO CONTROL THE AIRPLNE'S DESCENT. AS THE PARACHUTE DEPLOYED, IT BECAME ENTANGLED WITH THE ENGINE PROPELLER AND WAS DAMAGED AND ONLY PARTIALLY INFLATED. THE AIRPLANE DESCENDED AND STRUCK THE GROUND AT ABOUT 50 MPH. THE AIRPLANE AND PILOT DID NOT QUALIFY FOR THE CONDITIONS OF THE ULTRALIGHT REGULATION EXEMPTION, AND THE VEHICLE IS CONSIDERED TO BE AN AIRPLANE.

## Aircraft

- Registration: UNREG (not matched to a registry record)
- Reported make and model: BEIERLE THUNDER GULL J (THUNDER GU)
- Category: Ultralight, amateur-built
- Serial number: 1
- Airframe hours: 41
- Engines: BOMBARDIER ROTAX 503 53 horsepower reciprocating
- Damage: Destroyed
- Flight: Part 91
- Operator: Mark Beierle
- Last inspection: Unknown, January 2, 2000
- Departed: NONE, SANTA MARGARITA, CA

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 37; private; airplane ratings: single-engine land; medical: expired; seat: front; flight hours: 3,000 total, 60 in the last 90 days, 41 in the last 30 days, 6 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Visibility: 20 statute miles
- Lowest ceiling: none
- Temperature: 100 °F

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.

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