# NTSB SEA93LA181: Hiller UH-12E, N9785C, Auburn, WA, August 23, 1993 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 22, 1993, 17:00 local (Aug 23, 1993, 00:00 UTC) - Place: Auburn, WA - Coordinates: 47.299484, -122.31092 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=47.2995&lon=-122.3109&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report August 1, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 41752 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA93LA181 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41752/pdf - Page: https://openairdocs.org/ntsb/SEA93LA181 ## Probable cause FAILURE OF THE CONNECTING ROD BOLT. THE HIGH VEGETATION WAS A FACTOR. ## 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, takeoff - initial climb - engine assembly,connecting rod bolt - failure,total (cause) - Forced landing, descent - emergency - In flight collision with terrain/water, descent - emergency - terrain condition - high vegetation (contributing factor) ## Analysis DURING A SIGHTSEEING FLIGHT, THE PILOT HEARD A SERIES OF POPS AND THE WARNING LIGHTS FOR THE OIL PRESSURE AND TEMPERATURE ILLUMINATED. THE PILOT INITIATED AN AUTOROTATION TO AN OPEN FIELD. DURING THE LANDING MANEUVER, THE TAIL ROTOR WAS SEPARATED. AN ENGINE INSPECTION REVEALED THAT THE NUMBER 4 CONNECTING ROD SHANK WAS BROKEN INTO THREE PIECES. A METALLURGICAL EXAMINATION OF THE CONNECTING ROD ASSEMBLY REVEALED THAT THE CONNECTING ROD BOLT DISPLAYED A FRACTURE TYPICAL OF A TENSILE OVERSTRESS SEPARATION. THE OTHER CONNECTING ROD BOLT WAS NOT LOCATED. ## Factual narrative On August 22, 1993, at 1700 hours Pacific daylight time, a Hiller UH-12E, N9785C, experienced a loss of engine power shortly after takeoff from the Auburn Airport, Auburn, Washington. The pilot initiated an autorotation to an open field approximately one mile south of the airport. During the landing, the tail rotor was severed. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local sightseeing flight that was conducted under 14 CFR 91. The helicopter was substantially damaged and the certificated commercial pilot and his two passengers were not injured. The pilot reported that he had been giving five minute sightseeing flights in the local area for most of the day. Just after takeoff and at approximately 500 feet above ground level, the pilot heard a series of pops and the warning lights for the oil pressure and oil temperature illuminated. The pilot initiated an autorotation to an open field that was covered with six foot tall grass and shrubs. During the landing maneuver, the tail rotor was severed by the main rotor blades. During a visual inspection of the engine at the accident site, it was found that oil covered the engine and the decking below the engine. The cooling shroud was removed and the top left half of the crankcase was broken exposing the connecting rods and pistons. A push rod and pieces of the hydraulic tappets were laying loose. The engine was removed from the helicopter and inspected. It was found that the number 4 connecting rod shank was in three pieces. The cap portion was broken into two pieces. One bolt was retrieved and in two pieces. The other bolt was not located. A metallurgical examination of these parts revealed that, "the bolt fracture was typical of a tensile overstress separation." The other broken piece of the connecting rod was secondary due to excessively high stresses. ## Aircraft - Registration: [N9785C](https://openairdocs.org/aircraft/N9785C), registered now, S/N 2269 (OpenAirDocs) - Reported make and model: HILLER UH-12E - Registry model: [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e) (registry code 4360122) (OpenAirDocs) - Registry engine: [Lycoming VO-540 series](https://openairdocs.org/engine/lycoming-vo-540-series) (registry code 41534, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 2269 - Airframe hours: 7181 - Engines: LYCOMING VO-540-C2A 305 horsepower reciprocating - Damage: Substantial damage - Flight: Part 91 - Operator: Mayse International - Registered owner: Mayse International - Airworthiness certificate: Standard, Normal - Last inspection: Continuous airworthiness, July 18, 1993, 58 hours before - Airport: S50, Auburn ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 41; commercial, military; airplane ratings: multi-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--no waivers/lim.; seat: center; flight hours: 1,892 total, 31 in this make and model, 1,154 as pilot in command, 31 in the last 90 days, 19 in the last 30 days, 7 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 3 knots - Visibility: 50 statute miles - Lowest ceiling: 10,000 ft overcast - Temperature: 73 °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 19930822030059A](https://openairdocs.org/incident/19930822030059A), Aug 22, 1993: Hiller UH12E, Auburn, WA, Substantial damage. Through a connecting rod on takeoff. Autorotated into heavy brush. Severed tail rotor. ## Other investigations on N9785C (4) 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 SEA04LA073](https://openairdocs.org/ntsb/SEA04LA073), Apr 26, 2004: Hiller UH-12E (N9785C), Haines, OR, substantial damage. Probable cause: A momentary partial loss of power for undetermined reason(s) and the pilot's failure to maintain adequate RPM during his autorotation landing. - [NTSB SEA76FYC45](https://openairdocs.org/ntsb/SEA76FYC45), May 14, 1976: Hiller Acft UH-12E (N9785C), Tillamook, OR, destroyed - [NTSB SEA66A0066](https://openairdocs.org/ntsb/SEA66A0066), Jun 13, 1966: Hiller UH-12E (N9785C), Huntington, OR, substantial damage - [NTSB UNK64X1354](https://openairdocs.org/ntsb/UNK64X1354), Apr 17, 1964: Hiller 12E (N9785C), Pomeroy, WA, substantial damage 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.