Individually Owned: 150,657
Corporate Owned: 137,281
Aircraft Accident/Incident Report
Iliamna, Alaska 99606
Tuesady, May 12, 2009 13:30 AKD
NTSB Narrative Summary Released at Completion of Accident
The commercial pilot was on a public use helicopter flight in support of a state agency under Title 14, CFR Part 91. The pilot reported that shortly after takeoff he felt a vibration in the anti-torque pedals he had not felt before, and he noticed a slight yawing motion. He said the vibrations turned to oscillations, in both yaw and pitch, to the degree he felt the helicopter was going to come apart. He reported he made a descent while fighting to maintain control. The pilot said he touched down with 5-10 knots of forward airspeed, and subsequently the main rotor contacted the tailboom. He said after the accident he recalculated the weight and balance, and determined that the helicopter was loaded under the gross weight, but forward of the forward center of gravity (CG)limit about 1.1 inch. Research by the NTSB investigator-in-charge disclosed that operators of the same model helicopter were aware of similar events, and that the condition had been dubbed as "chugging." Further research revealed that similar accidents had been reported. Following a similar accident in Ireland the manufacturer reported to authorities that there were no further vibration issues, and that they would not be issuing a service bulletin. The manufacturer said they were familiar with the phenomenon known as chugging, and that they had conducted flight tests related to the phenomena. The tests determined that an oscillation may develop at high gross weight, about 90-100 knots, and that the oscillation was more of a "bucking" movement due to the fore-and-aft movement of the rotor mast. According to the manufacturer, the tests determined that chugging could occur within the normal CG range, most typically at or near a gross weight with a CG near the forward limit. The manufacturer believes that the oscillation is not destructive to the helicopter, and that the oscillation can be mitigated by the application of power. The manufacturer attributes the oscillation to the degree of firmness of the transmission mounts. Currently there are no manufacturer service bulletins or FAA Safety Alerts referencing the phenomena, and there is no manufacturer provided pilot training or guidance pertaining to chugging and its remedy.
NTSB Probable Cause Narrative
The main rotor transmission mount design, which resulted in an in-flight vibration/oscillation, and damage to the helicopter during an emergency descent and hard landing. Contributing to the accident was the lack of information from the manufacturer regarding this known flight oscillation, and loading the helicopter beyond the forward center of gravity limit by the pilot.
Event Information
| Type of Event | Accident |
| Event Date | 5/12/2009 |
| Event Day of the Week | Tuesday |
| Time of Event | 1330 |
| Event Time Zone | -- |
| Event City | Iliamna |
| Event State | ALASKA |
| Event Country | -- |
| Zipcode of the event site | 99606 |
| Event Date Year | 2009 |
| Event Date Month | 5 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | 600416N |
| Event Location Longitude | 1564316W |
| Event Location Airport | -- |
| Event Location Nearest Airport ID | -- |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | -- |
| Weather Briefing Completeness | -- |
| Investigator's weather source | Pilot |
| Time of the weather observation | |
| Direction of event from weather observation facility (degrees) | -- |
| Weather Observation Facility ID | -- |
| Elevation of weather observation facility | -- |
| Distance of event from weather observation facility (units?) | -- |
| Time Zone of the weather observation | -- |
| Lighting Conditions | Day |
| Lowest Ceiling Height | -- |
| Lowest Non-Ceiling Height | -- |
| Sky/Lowest/Cloud Conditions | Clear |
| Sky Condition for Lowest Ceiling | None |
| Visibility Runway Visual Range (Feet) | -- |
| Visibility Runway Visual Value (Statute Miles) | -- |
| Visibility (Statute Miles) | 10 |
| Air Temperature at event time (in degrees celsius) | -- |
| Dew Point at event time (in degress fahrenheit) | -- |
| Wind Direction (degrees magnetic) | -- |
| Variable Wind Indicator | -- |
| Wind Speed (knots) | -- |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | -- |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | -- |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | None |
| On Ground, Fatal Injuries | -- |
| On Ground, Minor Injuries | -- |
| On Ground, Serious Injuries | -- |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | 3 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 26568 |
| NTSB Notification Source | FAA Anchorage, ROC |
| NTSB Notification Date | -- |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | -- |
| Date of most recent change to record | Jan 28 2010 4:32PM |
| User who most recently changed record | stam |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N7196H |
| NTSB Number | ANC09GA040 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Public Use |
| Type of Flight Plan filed | Company VFR |
| Flight plan Was Activated? | -- |
| Damage | Substantial |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | ROBINSON HELICOPTER |
| Aircraft Model | R44 |
| Aircraft Series Identifier | -- |
| Aircraft Serial Number | 0994 |
| Certified Max Gross Weight | 2400 |
| Aircraft Category | Helicopter |
| Aircraft Registration Class | -- |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 4 |
| Number of Engines | 1 |
| Fixed gear or retractable gear | Fixed |
| Aircraft, Type of Last Inspection | 100 Hour |
| Date of Last Inspection | Aug 25 2008 12:00AM |
| Airframe hours since last inspection | -- |
| Airframe Hours | 1535 |
| ELT Installed | Yes |
| ELT Activated | No |
| ELT Aided Location of Event Site | No |
| ELT Type | C126 |
| Aircraft Owner Name | STATE OF ALASKA |
| Aircraft Owner Street Address | 4827 AIRCRAFT DR |
| Aircraft Owner City | ANCHORAGE |
| Aircraft Owner State | AK |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 99502-1071 |
| Operator is an individual? | No |
| Operator Name | STATE OF ALASKA |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | 4827 AIRCRAFT DR |
| Operator City | ANCHORAGE |
| Operator State | AK |
| Operator Country | USA |
| Operator Zip code | 99502-1071 |
| Operator Code | -- |
| Owner has at least one certificate | None |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | -- |
| Operator Certificate Number | -- |
| Indicates whether an air carrier operation was scheduled or not | -- |
| Indicates Domestic or International Flight | -- |
| Operator carrying Pax/Cargo/Mail | -- |
| Type of Flying (Per_Bus / Primary) | -- |
| Second Pilot on Board | No |
| Departure Point Same as Event | Yes |
| Departure Airport Code | -- |
| Departure City | Iliamna |
| Departure State | AK |
| Departure Country | USA |
| Departure Time | 1330 |
| Departure Time Zone | ADT |
| Destination Same as Local Flt | dest & departure same, accident can occur anywhere |
| Destination Airport Code | -- |
| Destination City | Iliamna |
| Destination State | AK |
| Destination Country | USA |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Jun 5 2009 4:41PM |
| User who most recently changed record | lewl |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | N/A |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |