Passengers of Flight NZ268 talk about their experience when the plane went through some heavy turbulence.

Passengers onboard an Air New Zealand flight which struck severe turbulence, injuring four onboard, have described the terror in the air.

NZ268 from Ho Chi Minh City to Auckland was forced to turn back to Vietnam on Sunday morning as a result of the incident.

Three cabin crew members and one passenger onboard received "minor injuries", an Air New Zealand spokeswoman said.



One passenger described it as the "flight from hell", and said the turbulence occurred during the meal service.

Air New Zealand currently flies the Boeing 767-300 on the Auckland-Vietnam route.

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Passengers arriving in Auckland on Monday night, on a rescheduled flight, said there was screaming and panic during the incident.

"It was really sudden," passenger Ben O'Brien said.

Air New Zealand recently announced the Boeing 787-9 Dreamliner will service the Auckland to Vietnam route.

"We were just flying along and there were a few bumps, then the captain came on the intercom and said 'hey everyone there is a little bit of turbulence' then suddenly, wham. There were some screams and they started saying 'is there a doctor on the flight'.

"People started running up and down with med kits and obviously the doctors got there and after a little bit of deliberation they said they had to turn back because the nearest city was Ho Chi Minh so we turned around.

"The did say it was serious [the nature of the injuries] and the feeling was if it was less serious we would have continued on to Darwin."

O'Brien said he was sitting near the front of the plane, but it was felt more towards the back of the plane.

"The people who got injured were down the back.

"It was very, very sudden - that's what made it so nasty."

Another passenger, David Hyndman said food went everywhere and one of the cabin crew hit the ceiling.

"A hostess went through the lighting cavity at the back where they prepare the food."

Neil Brown said there were "quite a few screams. It it was over pretty quickly".

"The cabin crew were seriously injured and had bad head injuries."

The Air New Zealand spokeswoman said the aircraft encountered turbulence about 40 minutes into the flight, returning to Ho Chi Minh around 8.20am Sunday (New Zealand time).

Those injured had been assessed and treated by medical staff, the spokeswoman said.

Passengers had to be accommodated in Ho Chi Minh City overnight as the service was delayed due to crewing numbers.

The flight departed around 7am on Monday.

TYPES OF TURBULENCE

There are four main types of turbulence:

- Convective turbulence, caused by thunderstorms formed as the sun heats the land and warm, moist air rises and cools into clouds. When the clouds can't hold any more water, it rains, causing a downdraft of cold air and wind.

- Mechanical turbulence, which happens when wind encounters tall obstructions, such as mountains, trees or buildings that disrupt its smooth flow.

- Wake turbulence, when one aircraft flies through the "wake" of another aircraft, much like the wake of a boat on the water. This is usually only a problem near airports.

- Clear-air turbulence, which typically occurs in the high atmosphere with variations of wind in jet streams — currents of air in the Earth's atmosphere caused by the planet's rotation and heating by the sun. This type of turbulence cannot be detected visually.

In January, an Air New Zealand flight from Tokyo to Auckland encountered unexpected strong turbulence during its dinner service, causing food to be splashed onto the ceiling and leaving passengers screaming and crying.

Some passengers had to be reviewed by on-board doctors after the event.

At the time Dave Reynolds, senior technical officer for the New Zealand Air Line Pilots' Association, said the likely culprit was clear-air turbulence.

"That can be quite nasty because it just hits you... it cannot be predicted."