# NTSB LAX93LA111: Cobb Intl Exec 90, N89678, Chandler, AZ, February 9, 1993

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: February 9, 1993, 14:55 local (21:55 UTC)
- Place: Chandler, AZ
- Coordinates: 33.239109, -111.779136 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=33.2391&lon=-111.7791&mi=10
- Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report November 15, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27918
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX93LA111
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27918/pdf
- Page: https://openairdocs.org/ntsb/LAX93LA111

## Probable cause

THE MANUFACTURER'S INADEQUATE QUALITY CONTROL WHICH RESULTED IN THE FATIGUE OF THE VALVE STEM.  THE SOFT TERRAIN CONTRIBUTED TO THIS ACCIDENT.

## Sequence of events

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

- Loss of engine power(total) - mech failure/malf, takeoff - initial climb
  - engine assembly,valve,intake - fatigue (cause)
  - inadequate quality control, manufacturer (cause)
- Forced landing, descent - emergency
- Nose down, landing - flare/touchdown
  - terrain condition - soft (contributing factor)

## Analysis

THE HELICOPTER'S ENGINE FAILED WHILE ON THE CROSSWIND LEG.  THE SURROUNDING TERRAIN WAS CONGESTED FORCING THE PILOT TO LAND IN AN AREA WHICH WAS DOWNWIND.  THE HELICOPTER NOSED DOWN ON LANDING IN THE SOFT TERRAIN.  EXAMINATION OF THE ENGINE DISCLOSED THAT AN INTAKE VALVE FAILED AND LODGED IN THE PISTON.  METALLURGICAL EXAMINATION REVEALED THAT THE VALVE STEM FAILED IN FATIGUE.  THE FATIGUE WAS PRECIPITATED BY THE MANUFACTURER'S IMPROPER QUALITY CONTROL WHICH FAILED TO ASSURE THAT THE VALVE WAS GROUND BEFORE IT WAS PLATED.

## Aircraft

- Registration: [N89678](https://openairdocs.org/deregistered/N89678-2001-06-26), registration cancelled 2001-06-26, S/N R.I. 5026 (OpenAirDocs)
- Reported make and model: COBB INTL EXEC 90
- Registry model: [Cobb Intl Inc DBA Rotorway INT ROTORWAY EXEC 90](https://openairdocs.org/model/cobb-intl-inc-dba-rotorway-int-rotorway-exec-90) (registry code 13017LM) (OpenAirDocs)
- Category: Helicopter
- Serial number: R.I. 5026
- Airframe hours: 541
- Engines: ROTORWAY 162 150 horsepower reciprocating
- Damage: Substantial damage
- Flight: Other work use, 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, January 11, 1993, 20 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 37; commercial, flight instructor; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 1,059 total, 611 in this make and model, 979 as pilot in command, 111 in the last 90 days, 55 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 270° at 12 knots
- Visibility: 35 statute miles
- Lowest ceiling: none
- Temperature: 61 °F

## 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 19930209002169A](https://openairdocs.org/incident/19930209002169A), Feb 9, 1993: Amtr ROTORWAYEXEC, Chandler, AZ, Substantial damage. Engine quit in pattern on test flight. Rocked on landing. Rolled. Engine had swallowed a valve. Stem not ground.

## Other investigations on N89678 (3)

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.

- [NTSB LAX00LA071](https://openairdocs.org/ntsb/LAX00LA071), Jan 4, 2000: Rotorway Exec 90 (N89678), Chandler, AZ, substantial damage. Probable cause: the fatigue fracture and separation of the secondary drive shaft, which resulted from the manufacturer's inadequate quality control process.
- [NTSB LAX96LA210](https://openairdocs.org/ntsb/LAX96LA210), May 22, 1996: Rotorway Exec 9 (N89678), Chandler, AZ, substantial damage. Probable cause: a loss of engine power due to a failed piston and piston ring in a critical phase of flight.
- [NTSB LAX94LA069](https://openairdocs.org/ntsb/LAX94LA069), Dec 8, 1993: Rotorway EXEC-90 (N89678), Chandler, AZ, substantial damage. Probable cause: THE FLIGHT INSTRUCTOR'S FAILURE TO PROPERLY FOLLOW THE AIRCRAFT BALLASTING PROCEDURES THAT RESULTED IN A LOSS OF CONTROL WHEN THE HELICOPTER'S CENTER OF GRAVITY LIMITS WERE EXCEEDED. INADEQUATE…

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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