# NTSB ANC03LA038: Hughes 369D, N90431, Tyonek, AK, March 31, 2003 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: March 31, 2003, 10:00 local (14:00 UTC) - Place: Tyonek, AK - Coordinates: 61.016666, -151.448883 - Nearby events: https://openairdocs.org/map.md?lat=61.0167&lon=-151.4489&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report September 30, 2003 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: FAA-AL-ANC FSDO 03 - NTSB case key (mKey): 56743 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC03LA038 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/56743/pdf - Page: https://openairdocs.org/ntsb/ANC03LA038 ## Probable cause The pilot's inadequate visual lookout while lifting into a hover to ensure the helicopter was clear of all objects, which resulted in separation of an external mirror that then struck and damaged a main rotor blade. Factors in the accident were the presence of a seismic cable, and high vegetation around the helicopter's takeoff spot. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Miscellaneous/other, hover - terrain condition - high vegetation (contributing factor) - object - other (contributing factor) - visual lookout - inadequate, pilot in command (cause) - miscellaneous,airframe - separation - rotor system,main rotor blade - foreign object damage ## Analysis The commercial certificated helicopter pilot was conducting external load operations in support of seismic operations, and landed a high skid-equipped helicopter in a confined area to pick up a passenger. The landing area had knee to waist level brush. The pilot did not exit the helicopter, but waited until the passenger climbed aboard. The pilot reported that the passenger unknowingly drug a seismic cable over the toe of the left skid as he climbed into the helicopter. As the pilot was lifting the helicopter into a hover, the cable slid aft into the helicopter's external load mirror. The cable severed the mirror from the helicopter, and the mirror was propelled upward, into the main rotor blades. The mirror then struck the vertical stabilizer. A postaccident examination of the rotor system revealed that one rotor blade sustained a dent on the underside of the blade. The director of operations stated that the damaged blade was beyond allowable repair limits, and had to be replaced. ## Factual narrative On March 31, 2003, about 1000 Alaska standard time, a Hughes 369D helicopter, N90431, sustained substantial damage when a main rotor blade and the vertical stabilizer were struck by a severed external load mirror as the helicopter was lifting into a hover, about 7 miles southwest of Tyonek, Alaska. The helicopter was being operated as a visual flight rules (VFR) external load operation under Title 14, CFR Part 133, when the accident occurred. The helicopter was operated by Prism Helicopters Inc., Wasilla, Alaska. The commercial certificated pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on April 4, the director of operations for the operator reported the pilot was lifting the helicopter into a hover in support of seismic operations. The director of operations said that as the pilot lifted off out of a confined area, he was not aware that the seismic cable was caught on the front toe of the left landing gear skid tube. As the helicopter gained altitude, the cable slid aft into the helicopter's external load mirror. The cable severed the mirror from the helicopter, and the mirror was propelled upward, into the main rotor blades. The mirror then struck the vertical stabilizer. In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the pilot, the pilot indicated that he landed the high skid-equipped helicopter in an area of knee to waist level brush to pick up the passenger. The pilot did not exit the helicopter, but waited until the passenger climbed aboard. The pilot reported that the passenger "apparently drug the seismic cable (black, less than 1 centimeter diameter) over toe of skid, unbeknownst to either the pilot or passenger." A postaccident examination of the rotor system revealed that one rotor blade sustained a dent on the underside of the blade. The director of operations stated that the damaged blade was beyond allowable repair limits, and had to be replaced. ## Aircraft - Registration: N90431 (not matched to a registry record) - Reported make and model: Hughes 369D - Category: Helicopter - Serial number: 1100833D - Airframe hours: 11172 - Engines: Allison 250-C20B 420 horsepower turbo shaft - Damage: Substantial damage - Flight: Other work use, Part 133 - Operator: Prism Helicopters Inc. - Registered owner: Wells Fargo Bank Nw, Trustee - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, February 27, 2003, 67 hours before - Departed: TYONEK, AK - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 44; injuries: none; commercial; instrument ratings: helicopter; medical: class 2, valid medical--w/ waivers/lim; last flight review April 26, 2002; seat: left; flight hours: 9,600 total, 2,100 in this make and model, 8,600 as pilot in command, 98 in the last 90 days, 67 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 200° at 5 knots - Visibility: 30 statute miles - Lowest ceiling: none - Temperature: 19 °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 20030331005699A](https://openairdocs.org/incident/20030331005699A), Mar 31, 2003: Hughes 369D, Tyonek, AK, Minor damage. (-23) Pilot dropped off passenger in lz, then repositioned the aircraft. The lz had high brush and was a tight area for blade clearance. The pilot returned to… 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.