Key Points:

Blind spots in two airplanes were the main cause of a mid-air collision that killed two pilots near Palmerston North this year, the Civil Aviation Authority (CAA) says.

Two Massey University School of Aviation planes collided in February as their pilots were flying exercises as part of tests for Commercial Pilot Licences.

Brandon James Gedge, 20, of Tauranga, and Dae Jin Hwang, 27, of West Auckland were found dead in their cockpits after their single-engine Piper Cherokee trainers crashed onto farmland.

Both were advanced aviation students.

CAA found the planes collided at an altitude of 472m and it would have been impossible for either pilot to survive.

The investigation concluded the pilots could not see each other as a result of the planes' inherent blind spots and, because for much of the time one was climbing, it was headed directly towards the sun.

Both pilots held private pilot licences, had appropriate experience for the training and had been briefed and appropriately authorised for the sequences they were to fly.

Both of the aircraft had valid airworthiness certificates, had been maintained in accordance with normal aviation practice, and been operating in a normal manner prior to the collision.

As a result of the accident Massey University School of Aviation implemented new procedures to ensure that the flight authorisation book now reflected the anticipated training area to be used by each flying school aircraft; and there were formal briefings between instructors and the duty instructor to limit the number of Massey school aircraft in each training area.