# NTSB LAX95LA271: Hughes 269C, N747MK, Redlands, CA, July 27, 1995 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: July 27, 1995, 16:45 local (23:45 UTC) - Place: Redlands, CA - Coordinates: 34.059616, -117.169387 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=34.0596&lon=-117.1694&mi=10 - Phase of flight: [Standing](https://openairdocs.org/ntsb-phases/150) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor, 1 uninjured - Status: Completed, report January 29, 1996 - Report: Approved by Office Director - NTSB case key (mKey): 29166 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX95LA271 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/29166/pdf - Page: https://openairdocs.org/ntsb/LAX95LA271 ## Probable cause The company's maintenance personnel improper servicing of the landing skid actuators. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Roll over, standing - idling rotors - landing gear,main gear shock absorbing strut - low pressure (cause) - maintenance,pressurizing - improper, company maintenance personnel (cause) ## Analysis THE HELICOPTER EXPERIENCED GROUND RESONANCE DURING THE COOL DOWN PERIOD AFTER LANDING AND SUBSEQUENTLY ROLLED OVER ON ITS SIDE. THE ENGINE AND MAIN ROTOR RPM WAS INSUFFICIENT FOR THE PILOT TO EFFECT A CORRECTIVE LIFTOFF. EXAMINATION OF THE LANDING GEAR ACTUATORS DISCLOSED THAT THEY WERE NOT FULLY CHARGED. ONE ACTUATOR'S REQUIRED BAFFLE WAS NOT REINSTALLED AFTER A FIELD REPAIR. ## Factual narrative On July 27, 1995, at 1645 hours Pacific daylight time, a Hughes 269C helicopter, N747MK, encountered ground resonance and rolled over during the postflight cool down period at Redlands Municipal Airport, Redlands, California. The pilot was completing a local visual flight rules personal flight. The helicopter, registered to and operated by M.I. Air Corporation, Redlands, California, sustained substantial damage. The certificated private pilot was not injured; however, his passenger sustained minor injuries. Visual meteorological conditions prevailed. The flight originated at the airport at 1545 hours. The pilot said in the aircraft accident report that after departing the airport with a passenger, he flew in the local area and returned at 1620 hours. The passenger deplaned and another passenger boarded the helicopter. He departed on a local flight and returned at 1645 hours. During the landing, he felt the helicopter enter the beginning stages of ground resonance. He immediately lifted the helicopter to a 3-foot hover and the ground resonance dissipated. While in the hover, he decided to do some hover pedal turns. During the turn to the right, the pilot noticed that the winds were gusting erratically and he elected to land. The touchdown was smooth and the initial cool down period was normal at 2,800 rpm. After the engine cylinder head temperature decreased, the pilot reduced the engine speed to 2,000 rpm. During the power reduction, the helicopter began to vibrate and between 2 and 3 seconds later, ". . . the helicopter was in pieces . . . ." The passenger repeated the pilot's statement as to the sequence of events. She said that during the cool down period the helicopter began to shake, slowly at first, and then violently. The helicopter "tipped over" and came to rest on its right side. Investigators sent the helicopter's four landing gear actuators and three elastomeric dampers to Schweizer Aircraft Corporation for functional testing and examination. The testing and examination were done under the supervision of a Federal Aviation Administration principal maintenance inspector from the Rochester [New York] Flight Standards District Office. The inspector reported that the testing was accomplished on September 8, 1995. He said that the actuators were improperly charged and that the right rear actuator was disassembled. The disassembly examination revealed that a required baffle, P/N 269A3167, was not installed. The inspector also said that the elastomeric dampers were severely overloaded. A Schweizer Aircraft Corporation engineer said that the baffle, used to deflect the hydraulic fluid from the compressed gasses, is installed on all actuators when manufactured. He said that the company authorized field maintenance personnel to repair the actuators. He said that the baffle was inadvertently not reinstalled. An actuator without the baffle could cause the piston to fully compress and give erratic damping action. The engineer also said that a low charged actuator would exceed the compression limits and affect the phasing of the main rotor system. This condition would lead to ground resonance. ## Aircraft - Registration: [N747MK](https://openairdocs.org/deregistered/N747MK-2008-07-03), registration cancelled 2008-07-03, S/N 1050442, built 1975 (OpenAirDocs) - Reported make and model: Hughes 269C - Registry model: [Hughes 269C](https://openairdocs.org/model/hughes-269c) (registry code 4470504) (OpenAirDocs) - Registry engine: [Lycoming HIO-360 series](https://openairdocs.org/engine/lycoming-hio-360-series) (registry code 41524, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 1050442 - Airframe hours: 5694 - Engines: LYCOMING HIO-360-DIA 190 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: M.I. Air Corporation - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, June 26, 1995, 50 hours before - Departed: L12 - Airport: L-12, Redlands ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 27; private; medical: class 3, valid medical--no waivers/lim.; seat: left; flight hours: 70 total, 70 in this make and model, 34 as pilot in command, 3 in the last 90 days, 1 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 10 knots, gusting 15 - Visibility: 5 statute miles - Lowest ceiling: none - Temperature: 102 °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 19950727019739A](https://openairdocs.org/incident/19950727019739A), Jul 27, 1995: Hughes 269C, Redlands, CA, Substantial damage. After landing during cool down began vibration. Tipped over. Skid dampers lacked baffles. Erratic damping action. 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.