NTSB LAX90LA137 — 1990-04-04 · LA VERNE, California, United States

N739B has since been reassigned. It is now registered to a different aircraft (SPORT COPTER VORTEX, built 2007), which was not involved in this event.

Aircraft involved

N739B Bell 47G None

Probable cause & findings

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.

Factual narrative

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. Source: NTSB Aviation Accident Database (Pre-2008 Archive) Retrieved: 2026-02-12

Verbatim from NTSB's published report. Source file NTSB_1990_LAX90LA137.txt. Findings + structured fields enriched from FAA avall.mdb. Full investigation docket on data.ntsb.gov ↗.

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