# NTSB LAX92LA214: Cobb Intl Exec 90, N7656T, Glendale, AZ, May 22, 1992

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: May 22, 1992, 11:30 local (18:30 UTC)
- Place: Glendale, AZ
- Coordinates: 33.529682, -112.310646 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=33.5297&lon=-112.3106&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report September 28, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27622
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX92LA214
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27622/pdf
- Page: https://openairdocs.org/ntsb/LAX92LA214

## Probable cause

THE IMPROPER CARBURETOR IDLE ADJUSTMENT BY COMPANY MAINTENANCE PERSONNEL. CONTRIBUTING TO THIS ACCIDENT WAS THE CFI'S INABILITY TO ATTAIN ADEQUATE RPM AND THE SOFT DIRT.

## Sequence of events

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

- Loss of engine power(total) - nonmechanical, descent
  - maintenance,adjustment - improper, company maintenance personnel (cause)
- In flight collision with terrain/water, descent - uncontrolled
  - rotor rpm - not maintained, pilot in command(cfi) (contributing factor)
- Roll over, landing - flare/touchdown
  - terrain condition - soft (contributing factor)

## Analysis

THE FLIGHT DEPARTED THE AIRPORT ON A LOCAL INSTRUCTIONAL FLIGHT.  WHEN THE FLIGHT RETURNED TO THE AIRPORT THE CFI INSTRUCTED THE NONCERTIFICATED STUDENT PILOT TO EXECUTE A SIMULATED ENGINE OUT AUTOROTATION.  THE STUDENT PILOT ENTERED THE AUTOROTATION AT A LOW MAIN ROTOR RPM, BUT DURING THE DESCENT THE RPM INCREASED TO THE LOW SIDE OF ITS NORMAL OPERATING RANGE. THE CFI ATTEMPTED TO TERMINATE THE AUTOROTATION AT 200 FEET AGL BECAUSE OF THE MARGINAL LOW ROTOR RPM, BUT WHEN HE APPLIED RAPID FULL THROTTLE THE ENGINE FALTERED AND THEN FAILED.  THE CFI EXECUTED AN EMERGENCY AUTOROATIVE LANDING.  ON TOUCHDOWN THE HELICOPTER BOUNCED, THE SKIDS DUG INTO THE SOFT DIRT ON THE SECOND TOUCHDOWN AND THE HELICOPTER CAME TO AN ABRUPT STOP AND ROLLED OVER. THE POST ACCIDENT ENGINE EXAMINATION DISCLOSED THAT THE ENGINE OPERATED NORMALLY THROUGHOUT ITS NORMAL OPERATIONAL PARAMETERS BUT WHEN THE THROTTLE WAS RAPIDLY APPLIED AFTER A PROLONGED IDLE THE ENGINE FALTERED. THE IDLE RPM WAS MARGINAL AND THE CARBURETOR HAD RECENTLY BEEN REPLACED.

## Aircraft

- Registration: N7656T (not matched to a registry record)
- Reported make and model: COBB INTL EXEC 90
- Category: Helicopter, amateur-built
- Serial number: RI-5001
- Airframe hours: 235
- Engines: Rotorway RI-162 150 horsepower reciprocating
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Operator: Cobb International, Inc., doing business as Rotorway International
- Registered owner: Cobb International, Inc.
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Continuous airworthiness, April 24, 1992, 38 hours before
- Airport: GEU, Glendale Muni Airport, runway 19, 5,350 × 75 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 36; commercial, flight instructor; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 695 total, 246 in this make and model, 615 as pilot in command, 174 in the last 90 days, 57 in the last 30 days, 5 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 35 statute miles
- Lowest ceiling: none
- Temperature: 81 °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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