# NTSB LAX97LA224: Enstrom F-28-F, N99YC, Riverside, CA, June 25, 1997 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: June 25, 1997, 12:43 local (19:43 UTC) - Place: Riverside, CA - Coordinates: 33.899978, -117.400321 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.9000&lon=-117.4003&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 3 minor - Status: Completed, report February 2, 1998 - Report: Approved by Office Director - NTSB case key (mKey): 29821 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX97LA224 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/29821/pdf - Page: https://openairdocs.org/ntsb/LAX97LA224 ## Probable cause failure by unknown maintenance personnel to retorque the nuts on the retainer cover. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(partial) - mech failure/malf, climb - to cruise - engine assembly,rocker arm/tappet - shifted (cause) - engine assembly,rocker arm/tappet - loose part/bolt/nut/clamp/etc (cause) - engine assembly,valve,intake - inoperative (cause) - maintenance,installation - not verified, other maintenance personnel (cause) - Hard landing, descent - emergency - autorotation - not performed, pilot in command (contributing factor) ## Analysis During takeoff, the helicopter lost power and landed hard. Postaccident examination revealed the No. 2 cylinder intake valve rocker shaft migrated out of the shaft bosses of the cylinder head. The shaft, cover, and nuts were found; the washers were not. According to owner/pilot there were internal star washer imprints on the cover plate commonly caused by torque or tightening of the nut. The helicopter had 61.5 total hours since new, and received one 50-hour inspection since delivery to the owner/pilot. The owner/pilot changed the oil and filter just prior to the inspection. ## Factual narrative On June 25, 1997, at 1243 hours Pacific daylight time, an Enstrom F-28-F helicopter, N99YC, was substantially damaged after a loss of power during a takeoff/climb at Riverside, California. The pilot and two passengers received minor injuries. Visual meteorological conditions prevailed for the local flight and no flight plan was filed. The flight was destined for Corona Airport, Corona, California. According to the pilot, the loss of engine power occurred less than 200 feet agl. He attempted an auto rotation and landed hard. Postaccident examination of the engine revealed that the intake valve rocker shaft migrated out of the shaft bosses of the cylinder head. The shaft, cover, and nuts were found; the washers were not. The pilot stated that there were internal star washer imprints on the cover plate that is commonly caused by the torque or tightening of the nut. The helicopter had 61.5 total hours since new and received one inspection at 50.9 hours since delivery to the owner/pilot. The owner/pilot changed the oil and filter prior to the formal 50-hour inspection by a private contractor. The inspection form revealed no specific inspection of the retainer plates are required except for a general condition inspection of the engine, accessories, and of the fluid systems for leaks. ## Aircraft - Registration: [N99YC](https://openairdocs.org/deregistered/N99YC-2018-01-24), registration cancelled 2018-01-24, S/N 809, built 1997 (OpenAirDocs) - Reported make and model: Enstrom F-28-F - Registry model: [Enstrom F-28F](https://openairdocs.org/model/enstrom-f-28f) (registry code 3300412) (OpenAirDocs) - Registry engine: [Lycoming HIO-360 series](https://openairdocs.org/engine/lycoming-hio-360-series) (registry code 41524, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 809 - Airframe hours: 61 - Engines: Lycoming HIO-360-F1AD 205 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Stits Aircraft - Registered owner: Enstrom Helicopter - Airworthiness certificate: Standard, Normal - Last inspection: Unknown, May 19, 1997, 1 hours before - Departed: RAL, CA - Destination: L66, CORONA, CA - Airport: RAL, Riverside Municipal ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 76; commercial; airplane ratings: single-engine sea, multi-engine sea, single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; seat: left; flight hours: 2,500 total ## Weather - Conditions: Visual (VMC), Day - Wind: 300° at 9 knots - Visibility: 4 statute miles - Lowest ceiling: none - Observed at: KRA ## 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 19970625040829A](https://openairdocs.org/incident/19970625040829A), Jun 25, 1997: Enstrm F28F, Riverside, CA, Substantial damage. Engine quit on climbout 200 ft AGL unable auto landed hard. Intake valve rocker shaft came loose. New engine. (.4) during takeoff, the helicopter lost power… 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. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.