Porirua helicopter crash likely caused by 'unanticipated yaw', report says

The chopper crashed in shallow water in the Pauatahanui inlet in 2017. Photo / Supplied

An investigation has shown a phenomenon known as "unanticipated yaw" was probably responsible for a helicopter crash in Porirua three years ago.

Unanticipated yaw is when the body of the helicopter begins to move in the opposite direction to the rotors. It can be fixed if the pilot notices it and acts quickly.

Pilot Rick Lucas miraculously survived when he lost control of the chopper and crashed into the Pauatahanui inlet in May 2017.

The BK117 A-3 helicopter was being used to transport three 11-metre hardwood power poles.

Lucas was flying the first pole in a sling across the inlet when he lost control and ditched in to the shallow water. He escaped with minor injuries, but the helicopter was "substantially damaged", a Transport Accident Investigation Commission (TAIC) report said.

After an investigation, TAIC said there were no mechanical faults that would have contributed to the crash.

"The directional control of the helicopter was lost, likely due to unanticipated right yaw," the report said.

"Unanticipated yaw is a flight characteristic to which all types of single rotor helicopter can be susceptible at low speed, dependent usually on the direction and strength of the wind relative to the helicopter.

"It may be rapid and most often will be in the opposite direction of the rotation of the main rotor blades - i.e. right yaw where the blades rotate counter-clockwise.

"Swift corrective action is needed, otherwise loss of control and possible accident may result."

TAIC found several "significant anomalies" in the maintenance records for the helicopter, which had been left unresolved when the Civil Aviation Authority (CAA) issued it with a certificate of airworthiness.

It also discovered further issues with maintenance records for the same company's other aircraft.

TAIC said there was an issue with the CAA's process for entering second-hand imported aircraft into the New Zealand regulatory system, in that it was not clearly defined; was not clearly understood by some staff; and did not have the checks in place to ensure it was followed.

Pilot Rick Lucas suffered only minor injuries after crashing into the Pauatahanui inlet. Photo / Supplied

CAA has undertaken an independent review into the process.

Key lessons arising from the investigation included that pilots must remain vigilant against distraction while flying, watch out for unanticipated yaw, and that all maintenance and inspection tasks must be carried out in accordance with the rules.

Lucas has since appeared in court for making false statements to his medical examiner and the CAA, and failing to disclose he had been seeing a doctor for stress and anxiety-related issues, and that he was prescribed various medications "not considered compatible with aviation safety".

They included sleeping tablets and anti-depressant medications.

However his charges did not relate to the Porirua crash, and there was no evidence to suggest the medications or his medical conditions were a factor.