Overview
Two helicopters, a McDonnell Douglas AH-64D (the test aircraft, referred to as 'lead') and a McDonnell Douglas 520N (the chase aircraft), were involved in a midair collision during a night visual flight rules (VFR) operation. The flight originated from Chandler, Arizona, and was destined for the McDonnell Douglas Heliport in Mesa, Arizona.
Flight Details
The chase crew's mission was to surveil the area for the test crew and provide information about other air traffic or hazards. The destination heliport was located just north of Falcon Field. During the arrival, the lead crew notified the chase of a VHF frequency change to the Falcon Field Tower (ATCT) frequency. The chase acknowledged, which was the last known transmission from that aircraft. The lead then switched to the heliport's 'Apache Ramp Control' frequency. The ground control radio operator, monitoring that frequency, cleared the helicopter(s) to land on Runway 22 at the heliport.
Collision
Shortly after the clearance, the chase helicopter collided with the lead helicopter. During the midair collision, the main rotor blades of the chase struck the left wing and wing stores of the lead. The lead helicopter continued to a safe landing. However, the main rotor separated from the chase helicopter, and it crashed.
Investigation
An investigation revealed that the chase helicopter had converged on the lead helicopter from the left rear quadrant. An expletive of unknown source was transmitted on the ATCT frequency at about the time of the midair collision. Tests of the radios from the chase helicopter showed that both radios were set to the ATCT frequency.