Falcon Field Airport
Aircraft Accident/Incident Report

Fountain Hills, Arizona 85268
Tuesady, August 14, 2001 8:15 MST

NTSB Narrative Summary Released at Completion of Accident

A staff pilot for the manufacturer was providing a sales demonstration flight to a potential customer's pilot when yaw control of the helicopter was lost, it entered a spin, collided with the ground, and rolled over. During the flight the customer's typical aerial application pest control flight profile was to be flown. The customer pilot flew Bell 206's currently in the mission and had no experience in the NOTAR anti-torque system. The maneuver was a simulated aerial application pass followed by a turn around. The manufacturer's pilot said the maneuver was very docile and consisted of a pass down a creek bed at 60 knots and 50 feet. The customer pilot initiated a gentle cyclic pull-up to a 10- to 15-degree nose up attitude while entering a right turn as the helicopter decelerated. At the 90 degree point in the turn, the helicopter was at 40 to 50 knots with a 30-degree or less bank angle to the right. As the nose came around in the turn, the nose tucked down to about 20 degrees below the horizon. The manufacturer's pilot took over the controls and added near full aft cyclic to level the nose; at this point, he received a low rotor warning horn (indicating a rotor droop at 95 percent or lower). Coincident with the low rotor warning, the helicopter began a right yaw rate. He added full left pedal, but the yaw rate continued at what he described as a "slow pedal turn rate," eventually completing 4 to 6 complete revolutions. At this point the helicopter began descending and he added collective. He immediately got a "power" audio warning, indicating that he was exceeding the upper power limit of the engine. The right yaw rate also increased with collective input. The pilot then modulated the collective between the low rotor warning and the excessive power warning in an attempt to both control the yaw and stop the descent. As he lowered the collective and the rotor speed began to build, the yaw would slow, but the helicopter then began descending faster. As he added collective to slow the descent, the yaw rate would increase. As the helicopter neared the ground, the yaw finally stopped; however, the helicopter was translating sideways toward a berm. The helicopter touched down on the right skid against the berm and it rolled over. The manufacturer's pilot said his hands were following on the controls as the customer pilot flew and he did not perceive any unusual control inputs. He further stated that his feet were about 1 inch from the anti-torque pedals and he did not feel any inputs from the customer pilot on the pedals. Based on his extensive flight test experience in this helicopter, the manufacturer's pilot believes that the aft cyclic input to correct the nose down pitching moment induced a rotor droop, and that the droop was the initiating event in the yaw rate onset. He does not know how low the rotor speed went, but the warning is triggered at 95 percent Nr. The lower limit of the Nr green arc is at 90 percent. The NOTAR anti-torque control system uses air from a pedal controlled jet thruster nozzle on the end of the tail boom to provide anti-torque control. Additional yaw control is provided by vertical stabilizers, which are largely effective only above 20 to 30 knots. Air is supplied to the thruster by a fan driven by a power takeoff shaft from the main transmission. There is a direct relationship between the speed of the main rotor and the speed of the fan. The pilot said he believes that the initial yaw onset was because the rotor drooped low enough to slow the fan below the speed which could supply the necessary air volume to the thruster to control the yaw and they were not fast enough for the vertical stabilizers to have any effect. After the occupants had extricated themselves from the wreckage, the customer pilot asked the pilot what had happened. He replied to them that he didn't know what happened and added, "Maybe we should have turned to the left instead." The helicopter's FAA approved Rotorcraft Flight Manual (RFM) contains several warnings about low speed maneuvering. Under the heading "Unanticipated Right Yaw", the RFM section notes that an unanticipated right yaw can occur when operating at low altitude and airspeeds below 60 knots when a pilot's attention is distracted by events outside the helicopter and sufficient control inputs are not made to adjust for changing aerodynamic conditions. The paragraph states, "If no directional or cyclic control inputs are made, a nose down pitch and a right roll may follow the right yaw." The section notes that this is most likely to occur at speeds below 60 knots in uncoordinated right turns, while flying out of trim with too much right pedal, or right turns to a downwind condition. Examination of the helicopter revealed no evidence of a preimpact malfunction or failure of the control system.

NTSB Probable Cause Narrative

the manufacturer's pilot's failure to maintain yaw control and main rotor speed while recovering from an unusual attitude induced by the customer pilot's inadequate control inputs while maneuvering at low altitude. The manufacturer's pilot's inadequate supervision of the flight is also causal. A factor in the accident was the customer pilot's lack a familiarity with the NOTAR yaw control system.

Event Information

Type of Event Accident
Event Date 8/14/2001
Event Day of the Week Tuesday
Time of Event 815
Event Time Zone Mountain Standard Time
Event City Fountain Hills
Event State ARIZONA
Event Country --
Zipcode of the event site 85268
Event Date Year 2001
Event Date Month 8
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude 333500N
Event Location Longitude 1114000W
Event Location Airport Falcon Field
Event Location Nearest Airport ID FFZ
Indicates whether the acc/inc occurred off or on an airport Off Airport/Airstrip
Distance from airport in statute miles 11
Degrees magnetic from airport 30
Airport Elevation 1394
Weather Briefing Completeness Not pertinent
Investigator's weather source Weather Observation Facility
Time of the weather observation 747 Pacific Standard Time
Direction of event from weather observation facility (degrees) 210
Weather Observation Facility ID FFZ
Elevation of weather observation facility 1394
Distance of event from weather observation facility (units?) 10
Time Zone of the weather observation PST
Lighting Conditions Day
Lowest Ceiling Height 10000
Lowest Non-Ceiling Height --
Sky/Lowest/Cloud Conditions Clear
Sky Condition for Lowest Ceiling Broken
Visibility Runway Visual Range (Feet) --
Visibility Runway Visual Value (Statute Miles) --
Visibility (Statute Miles) 50
Air Temperature at event time (in degrees celsius) --
Dew Point at event time (in degress fahrenheit) --
Wind Direction (degrees magnetic) --
Variable Wind Indicator Variable
Wind Speed (knots) --
Wind Velocity Indicator Light and Variable
Wind Gust Indicator Not Gusting
Wind Gust (knots) --
Altimeter Setting at event time (in. Hg) 30.01
Density Altitude (feet) --
Intensity of Precipitation --
METAR weather report --
Event Highest Injury Minor
On Ground, Fatal Injuries --
On Ground, Minor Injuries --
On Ground, Serious Injuries --
Injury Total Fatal --
Injury Total Minor 3
Injury Total None 1
Injury Total Serious --
Injury Total All 3
Investigating Agency NTSB
NTSB Docket Number (internal use) 14786
NTSB Notification Source
NTSB Notification Date Aug 14 2001 12:00AM
NTSB Notification Time 1007
Fiche Number and/or location -used to find docket information DMS
Date of most recent change to record Feb 5 2004 4:26PM
User who most recently changed record NTSB\MONR
Basic weather conditions Visual Meteorological Cond
FAA District Office WP-FSDO Scottsdale, AZ

Aircraft Involved

Aircraft #1

Aircraft Registration Number N70457
NTSB Number LAX01FA277
Missing Aircraft Indicator --
Federal Aviation Reg. Part Part 91: General Aviation
Type of Flight Plan filed Company VFR
Flight plan Was Activated? No
Damage Substantial
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name MD HELICOPTERS, INC.
Aircraft Model 600N
Aircraft Series Identifier --
Aircraft Serial Number RN057
Certified Max Gross Weight 4100
Aircraft Category Helicopter
Aircraft Registration Class U.S. Registered/U.S. Soil
Aircraft is a homebuilt? No
Flight Crew Seats --
Cabin Crew Seats --
Passenger Seats --
Total number of seats on the aircraft 6
Number of Engines 1
Fixed gear or retractable gear Fixed
Aircraft, Type of Last Inspection Annual
Date of Last Inspection Apr 13 2001 12:00AM
Airframe hours since last inspection 47
Airframe Hours 361.2
ELT Installed No
ELT Activated No
ELT Aided Location of Event Site No
ELT Type --
Aircraft Owner Name MD Helicopters Inc.
Aircraft Owner Street Address 4555 E. McDowell Rd.
Aircraft Owner City Mesa
Aircraft Owner State AZ
Aircraft Owner Country USA
Aircraft Owner Zipcode 85215
Operator is an individual? No
Operator Name --
Operator Same as Owner? Yes
Operator Is Doing Business As --
Operator Address Same as Owner? Yes
Operator Street Address --
Operator City --
Operator State --
Operator Country --
Operator Zip code --
Operator Code --
Owner has at least one certificate None
Other Operator of large aircraft? --
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) Business
Second Pilot on Board Yes
Departure Point Same as Event No
Departure Airport Code FFZ
Departure City Falcon Field
Departure State AZ
Departure Country USA
Departure Time 745
Departure Time Zone MST
Destination Same as Local Flt dest & departure same, accident can occur anywhere
Destination Airport Code --
Destination City --
Destination State --
Destination Country --
Specific Phase of Flight Maneuvering
Report sent to ICAO? No
Evacuation occurred No
Date of most recent change to record Dec 3 2003 5:52PM
User who most recently changed record COOS
Since inspection or accident Time of Accident
Event Location Runway Number and Location --
Runway Length --
Runway Width --
Sight Seeing flight No
Air Medical Flight No
Medical Flight --