Ambulance staff met the plane's crew and transferred the patient to an ambulance.
Mr Anderson said everything and everyone was "fine" after the event.
"The main thing a pilot does when one engine goes out like that is to feather that propeller so the drag's gone and you're basically flying a single-engine airplane," he said.
"It's bloody annoying when it happens, but pilots are constantly practising those procedures for just such an eventuality."
He said the Mojave was nearing Wellington when the engine failed.
"Rather than fly into Wellington, where the weather wasn't very good, he was directed to land at Paraparaumu."
He said there had never been a similar incident in Air Wanganui's history.
The company operates two aircraft, both fitted out for medical flights.
"We're pretty much flying to Wellington every day, and sometimes two or three times a day," Mr Anderson said. The planes were maintained at Palmerston North by Feildair and service schedule was "very regular".
"It was our Piper Mojave, a piston-engined machine. It wasn't the King Air C90 turbo prop."
The aircraft in yesterday's incident was regarded as the back-up plane and was flying while the King Air was being serviced in Palmerston North, Mr Anderson said.
Mr Mauchline had been with the company three years and was very experienced.
"I know we play these things down, but frankly the response to the engine failure was routine," Mr Anderson said.
Air Wanganui provides a nationwide charter and air ambulance service, available 24 hours a day, seven days a week. Both its twin-engine planes are fully pressurised and have full intensive care facilities.
Kapiti Coast Airport chief executive Robert Binney said the plane made an unscheduled but "uneventful" landing.
