# NTSB LAX90LA137: Bell 47G, N739B, La Verne, CA, April 4, 1990

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: April 4, 1990, 13:58 local (20:58 UTC)
- Place: La Verne, CA
- Coordinates: 34.15036, -117.760665 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=34.1504&lon=-117.7607&mi=10
- Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report March 12, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 26770
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX90LA137
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/26770/pdf
- Page: https://openairdocs.org/ntsb/LAX90LA137

## Probable cause

THE HELICOPTER'S ROTOR SYSTEM BEING ALLOWED TO UNDERSPEED AS A RESULT OF IMPROPER USE OF FLIGHT CONTROLS BY THE DUAL STUDENT; IMPROPER SUPERVISION BY THE CERTIFIED FLIGHT INSTRUCTOR; AND DELAYED REMEDIAL ACTION BY THE CERTIFIED FLIGHT INSTRUCTOR WHICH ALLOWED THE IN FLIGHT COLLISION WITH THE RUNWAY.

## Sequence of events

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

- In flight collision with terrain/water, landing - flare/touchdown
  - rotor system - underspeed
  - flight controls - improper use of, dual student (contributing factor)
  - supervision - improper, pilot in command(cfi) (cause)
  - remedial action - attempted, pilot in command(cfi) (cause)

## Analysis

ACCORDING TO THE INSTRUCTOR PILOT, THE AIRCRAFT BEGAN TO VIBRATE DURING TERMINATION OF A POWER RECOVERY AUTOROTATION. HE STATED THAT WHEN THE COMMERCIALLY RATED STUDENT PILOT APPLIED POWER, THE ENGINE DEVELOPED POWER, BUT THE ROTOR RPM DECAYED. THE AIRCRAFT COLLIDED WITH THE RUNWAY. THE INSTRUCTOR PILOT WAS LATE IN TAKING THE CONTROLS AND RECOVERING THE AIRCRAFT. AN FAA AIRWORTHINESS INSPECTOR EXAMINED THE HELICOPTER AND FOUND NO PRE-IMPACT MECHANICAL MALFUNCTIONS OR FAILURES.

## Aircraft

- Registration: N739B (not matched to a registry record)
- Reported make and model: BELL 47G
- Category: Helicopter
- Serial number: 85
- Engines: LYCOMING VO-435 220 horsepower reciprocating
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Operator: Airborne Helicopters
- Airport: POC, Brackett, runway 26R, 3,661 × 75 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 40; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; flight hours: 2,000 total

## Weather

- Conditions: Visual (VMC), Day
- Wind: 30° at 5 knots
- Visibility: 12 statute miles
- Lowest ceiling: 2,500 ft broken
- Temperature: 64 °F, dew point 55 °F
- Observed at: ONT, 12 nm away

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19900404013889A](https://openairdocs.org/incident/19900404013889A), Apr 4, 1990: Bell 47G, La Verne, CA, Substantial damage. Collided with runway on practice auto rotation. Reported vibration rotor decay prior impact. No mechanical defects.

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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