Accident
The aircraft was conducting an air transport charter flight from Palmerston North to Christchurch, carrying one pilot and nine passengers. At 1907 hours, while performing an instrument approach to Christchurch Aerodrome at night in instrument meteorological conditions, it descended below the minimum altitude. The aircraft was in a position where reduced visibility prevented the runway or approach lights from being seen, and it collided with trees and terrain 1.2 nautical miles short of the runway. The pilot and seven passengers were killed, and two passengers received serious injury. The aircraft was destroyed.
Investigation
The investigation found that the pilot was appropriately licensed and rated for the flight. The pilot had previously unknown heart disease, which probably would not have affected his fitness for a Class 1 medical certificate or his ability to control the aircraft. The pilot's experience on the PA-31 type was in VFR operations, and his IFR experience was limited. He had completed a recent IFR competency assessment meeting regulatory requirements. The aircraft had a valid Certificate of Airworthiness and met maintenance requirements. The cabin heater had been returned to service by the operator after a maintenance engineer disabled it pending a required test; this was not appropriate but not a factor in the accident. Three avionics instruments were unserviceable, not complying with Rule part 135, but sufficient serviceable equipment remained for the IFR flight. The pilot permitted cellphone and computer use on the flight, which had the potential to cause electronic interference and was unsafe. The pilot's own cellphone was operating during the last three minutes of the flight and could have interfered with the glide slope indication on the ILS approach. However, the aircraft's continued descent below minimum altitude could not have resulted from electronic interference. The altimeter was correctly set and displayed correct altitude throughout. No aircraft defect caused the descent. The descent began before reaching the glide slope and continued below it, resulting either from a faulty glide slope indication or from the pilot flying a localiser approach instead of an ILS approach. When the aircraft descended below the minimum altitude for either approach, it was too far for the pilot to see the runway and approach lights in reduced visibility. The pilot allowed the aircraft to continue descending when he should have commenced a missed approach or stopped the descent. The pilot's actions—including flying a high-speed unstabilised instrument approach, reverting to hand-flying at a late stage, not using the autopilot for a coupled approach, and possibly his cellphone call—would have caused high workload, overload, and distraction. The pilot's failure to stop the descent probably arose from distraction or overload, leading to not monitoring the altimeter as the aircraft approached minimum altitude. The possibility of late incapacitation is unlikely but cannot be ruled out. If TAWS had been installed, it would have given timely warning to avert the collision. The search, though delayed by miscommunication of coordinates, was probably completed as expeditiously as possible.
Probable Cause
The accident probably resulted from the pilot becoming distracted from monitoring his altitude at a critical stage of the approach.