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B412, vicinity Karlsborg Sweden, 2003

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Summary
On 25 March 2003, the crew of a Bell 412 lost control of the aircraft as a result of pilot mishandling associated with the development of a Vortex Ring State.
Event Details
When March 2003
Actual or Potential
Event Type
Human Factors, Loss of Control
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft BELL B-412
Operator Swedish Armed Forces
Domicile Sweden
Type of Flight Military/State
Origin Karlsborg
Intended Destination Karlsborg
Take off Commenced Yes
Flight Airborne Yes
Flight Completed No
Flight Phase Manoeuvring
MNV
Location - Airport
Airport vicinity Karlsborg
HF
Tag(s) Ineffective Monitoring,
Manual Handling
LOC
Tag(s) Flight Management Error,
Flight Control Error"Flight Control Error" is not in the list (Airframe Structural Failure, Significant Systems or Systems Control Failure, Degraded flight instrument display, Uncommanded AP disconnect, AP Status Awareness, Non-normal FBW flight control status, Loss of Engine Power, Flight Management Error, Environmental Factors, Bird or Animal Strike, ...) of allowed values for the "LOC" property.,
Extreme Pitch
Outcome
Damage or injury No
Aircraft damage Hull loss
Injuries Few occupants
Fatalities Few occupants (1)
Causal Factor Group(s)
Group(s) Aircraft Operation
Safety Recommendation(s)
Group(s) Aircraft Operation,
Aircraft Airworthiness
Investigation Type
Type Independent

Description

On 25 March 2003, the crew of a Bell 412 lost control of the aircraft as a result of pilot mishandling associated with the development of a Vortex Ring State.

Summary

This is the Summary from the report published by the Swedish Accident Investigation Board:

"During the concluding Swedish Army exercise for 2003…a military ambulance helicopter based on the Karlsborg base took part. In connection with a rescue exercise, air-sea rescue open water (LÖV), the helicopter performed repeated sorties to assist simulated emergency cases in lakes in the vicinity of Karlsborg. In the final phase of the ninth sortie, the pilots lost control of the helicopter which, with a high rate of descent, struck the ice on Bottensjön lake. The ice broke on impact, the helicopter turned over onto its back and sank nose-first towards the bottom of the lake and with the rear of the fuselage against the edge of the ice at water level.

Three crew members were able to leave the helicopter and make their way up to the surface of the water and onto the ice. A fourth crew member drowned in the accident…

…Investigation revealed no technical faults or shortcomings that could have caused the accident.

…The accident was caused by the helicopter being manoeuvred into an aerodynamic situation in which, as its speed was being reduced to IAS=0, sank into its own downwash located diagonally in front of and below the helicopter. This aerodynamic situation developed into a vortex ring state (VRS) which became noticeable in the measurement data approximately 8 s before impact on the ice, whereafter the helicopter’s rate of descent could not be prevented despite increasing input of collective pitch. A contributory cause of the accident was the two pilots’ simultaneous manoeuvring of the helicopter. This allowed small or no chance of discovering in time that they were approaching the helicopter’s limit for safe flight."

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LOC

Further Reading

For further information see the full Report published by the Swedish Accident Investigation Board (SHK).