Palmerston North

The following findings were identified:
Findings are listed in order of development and not in order of priority.
- The crew was appropriately licensed and fit to conduct the flight.
- The captain was an experienced company line-training captain, familiar with the aircraft and route.
- The co-pilot while new to the Convair 580 was, nevertheless, an experienced pilot and had flown the route earlier in the week.
- The aircraft had a valid Certificate of Airworthiness and was recorded as being serviceable for the flight.
- The estimated aircraft weight and balance were within limits at the time of the accident.
- With a serviceable weather radar the weather was suitable for the flight to proceed.
- The captain was the flying pilot for the flight from Christchurch to Palmerston North.
- The flight proceeded normally until the aircraft levelled after passing Paraparaumu NDB.
- Why the aircraft was levelled at about 14 400 ft was not determined, but could have been because of increasing or expected turbulence.
- The weather conditions at around the time of the accident were extreme.
- The aircraft descended through an area of forecast severe icing, which was probably beyond the capabilities of the aircraft anti-icing system to prevent ice build-up on the wings and tailplane.
- The crew was probably aware of the presence of icing but might not have been aware of the likely speed and the extent of ice accretion.
- The rate of ice accretion might have left insufficient time for the crew to react and prevent the aircraft stalling.
- The transponder transmissions were impaired probably due to ice build-up on the aerials.
- The aircraft probably stalled because of a rapid build-up of ice, pitching the aircraft nose down and probably disorientating the crew. This could have resulted from a tailplane stall.
- Although the aircraft controls were probably still functional in the descent, a very steep nose down attitude, high speed and a potentially stalled tailplane, made recovery very unlikely.
- Under a combination of high airspeed and G loading, the aircraft started to break-up in midair, probably at about 7000 ft.
- Although there was no evidence to support the possibility of a mechanical failure or other catastrophic event contributing to the accident, given the level of destruction to ZK-KFU and that some sections of the aircraft were not recovered, these possibilities cannot be fully ruled out.
- The crew of AF 642 not being advised of the presence of a new SIGMET concerning severe icing should not have affected the pilotsí general awareness of the conditions being encountered.
- Had the crew been aware of the new SIGMET it might have caused them to be more alert to icing.
- Pilots awareness of the presence of potentially hazardous conditions would be increased if other pilots commonly sent AIREPs when such conditions were encountered.
- Operatorsí manuals, especially for IFR operators, might contain inadequate and misleading information for flight in adverse weather conditions.
- The search for the aircraft and pilots was competently handled in adverse conditions.
- The regular mandatory checks of the CVR failed to show that it was not recording on all channels.
- The lack of any intra cockpit voice recordings hampered and prolonged the investigation.
- The DFDR data and available CVR recordings provided limited but valuable information for the investigation.
- Had more modern and capable recorders been installed on ZK-KFU, significantly more factual information would have be available for the investigation, thus enhancing the investigation and increasing the likelihood of finding a confirmed accident cause, rather than a probable one.
- Had suitable ULB tracking equipment been available, the finding of the wreckage and recovery of the recorders would have been completed more promptly.
- The lack of tracking equipment could have resulted in the recorders not being found, and possibly even the wreckage not being found had it been in deeper water.

Findings:
- The pilot was appropriately licensed and rated for the flight.
- The pilotís previously unknown heart disease probably would not have made him unfit to hold his class 1 medical certificate.
- The pilotís ability to control the aircraft was probably not affected by the onset of any incapacitation associated with his heart condition.
- Although the pilot was experienced on the PA 31 type on VFR operations, his experience of IFR operations was limited.
- The pilot had completed a recent IFR competency assessment, which met regulatory requirements for recent instrument flight time.
- The aircraft had a valid Certificate of Airworthiness, and the scheduled maintenance which had been recorded met its airworthiness requirements.
- The return of the cabin heater to service by the operator, after the maintenance engineer had disabled it pending a required test, was not appropriate but was not a factor in the accident.
- The cabin heater was a practical necessity for IFR operations in winter, and the required test should have been given priority to enable its safe use.
- The 3 unserviceable avionics instruments in the aircraft did not comply with Rule part 135, and indicated a less than optimum status of avionics maintenance. However there was sufficient
serviceable equipment for the IFR flight.
- The use of cellphones and computers permitted by the pilot on the flight had the potential to cause electronic interference to the aircraftís avionics, and was unsafe.
- The pilotís own cellphone was operating during the last 3 minutes of the flight, and could have interfered with his glide slope indication on the ILS approach.
- The aircraftís continued descent below the minimum altitude could not have resulted from electronic interference of any kind.
- The pilotís altimeter was correctly set and displayed correct altitude information throughout the approach.
- There was no aircraft defect to cause its continued descent to the ground.
- The aircraftís descent which began before reaching the glide slope, and continued below the glide slope, resulted 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 away for the pilot to be able to see the runway and approach lights ahead in the reduced visibility at the time.
- The pilot allowed the aircraft to continue descending when he should have either commenced a missed approach or stopped the aircraftís descent.
- The pilotís actions or technique in flying a high-speed unstabilised instrument approach; reverting to hand-flying the aircraft at a late stage; not using the autopilot to fly a coupled approach and, if intentional, his cellphone call, would have caused him a high workload and possibly overload and distraction.
- The pilotís failure to stop the descent probably arose from distraction or overload, which led to his not monitoring the altimeter as the aircraft approached minimum altitude.
- The possibility that the pilot suffered some late incapacity which reduced his ability to fly the aircraft is unlikely, but cannot be ruled out.
- If TAWS equipment had been installed in this aircraft, it would have given warning in time for the pilot to avert the collision with terrain.
- While some miscommunication of geographical coordinates caused an erroneous expansion of the search area, the search for the aircraft was probably completed as expeditiously as possible in difficult circumstances.

The captain not ensuring the aircraft intercepted and maintained the approach profile during the conduct of the non-precision instrument approach, the captain's perseverance with his decision to get the undercarriage lowered without discontinuing the instrument approach, the captain's distraction from the primary task of flying the aircraft safely during the first officer's endeavours to correct an undercarriage malfunction, the first officer not executing a Quick Reference Handbook procedure in the correct sequence, and the shortness of the ground proximity warning system warning.

Failure of the crew to take the appropriate measures to follow the correct track. However, strong winds and the lack of radio navigational beacon was considered as a contributory factor.

Engine failure shortly after rotation.

A Board of Inquiry set up to investigate the accident found William Smillie guilty of 'culpable carelessness and neglect' and recommended to the Minister in Charge of the Air Dept that his 'A' licence be suspended for 3 months. The Board also disallowed the witness travelling expenses due to Mr. Smillie for attending the Inquiry and ordered that he pay the sum of 10 Pounds towards the Board's costs and expenses.