NTSB Identification: LAX94FA383A
Accident occurred Tuesday,
September 27, 1994 in MESA, AZ
Probable Cause Approval Date:
1/19/1996
Aircraft: MCDONNELL DOUGLAS 520N, registration: N520NT
Injuries:
1 Fatal, 1 Serious, 2 Uninjured.

A TEST HELICOPTER (MCDONNELL DOUGLAS AH-64D, WITH 1 VHF RADIO) AND A CHASE
HELICOPTER (MCDONNELL DOUGLAS 520N, WITH 2 VHF RADIOS) WERE ON A NIGHT VFR
FLIGHT FROM CHANDLER, AZ, TO THE MCDONNELL DOUGLAS HELIPORT AT MESA, AZ. THE
MISSION OF THE CHASE CREW (CHASE) WAS TO SURVEIL THE AREA FOR THE TEST CREW
(LEAD) AND TO PROVIDE INFORMATION CONCERNING OTHER AIR TRAFFIC OR HAZARDS. THE
DESTINATION HELIPORT WAS LOCATED JUST NORTH OF FALCON FIELD. DURING ARRIVAL,
LEAD NOTIFIED CHASE OF A VHF FREQUENCY CHANGE TO THE FALCON FIELD TOWER (ATCT)
FREQUENCY. CHASE ACKNOWLEDGED; THIS WAS THE LAST KNOWN TRANSMISSION FROM CHASE.
LEAD THEN CHANGED TO THE HELIPORT'S 'APACHE RAMP CONTROL' FREQUENCY. THE GROUND
CONTROL RADIO OPERATOR, MONITORING THE FREQUENCY, CLEARED THE HELICOPTER(S) TO
LAND ON RUNWAY 22 AT THE HELIPORT. SOON THEREAFTER, THE CHASE HELICOPTER
COLLIDED WITH THE LEAD HELICOPTER. DURING THE MIDAIR COLLISION, THE MAIN ROTOR
BLADES OF CHASE STRUCK THE LEFT WING AND WING STORES OF LEAD. LEAD CONTINUED TO
A SAFE LANDING, BUT THE MAIN ROTOR SEPARATED FROM THE CHASE HELICOPTER, AND IT
CRASHED. AN INVESTIGATION REVEALED THE CHASE HELICOPTER HAD CONVERGED ON THE
LEAD HELICOPTER FROM THE LEFT REAR QUADRANT. AN EXPLETIVE OF AN UNKNOWN SOURCE
WAS TRANSMITTED ON THE ATCT FREQUENCY AT ABOUT THE TIME OF THE MIDAIR COLLISION.
TESTS OF THE RADIOS FROM THE CHASE HELICOPTER REVEALED THEY WERE BOTH ON THE
ATCT FREQUENCY.

The National Transportation Safety Board determines the probable cause(s) of
this accident as follows:
FAILURE OF THE CHASE HELICOPTER PILOT TO MAINTAIN
CLEARANCE FROM THE LEAD HELICOPTER DURING A NIGHT APPROACH TO LAND. POSSIBLE
FACTORS RELATING TO THE ACCIDENT WERE: DARKNESS, AND INADEQUATE RADIO
COORDINATION BETWEEN FLIGHT CREWS OF THE TWO HELICOPTERS.

Full
narrative available

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