Stuff Travel can reveal almost 150,000 passengers will have their flights impacted after Air New Zealand was forced to ground two planes amid a global engine shortage.

Most of the affected passengers will have their flights moved within 90 minutes of their original departure, although around 4000 people will have their flights moved "a day either side."

The problem has come from a worldwide shortage of Pratt and Whitney engines which power the airline's fleet of A320neo and A321neo planes. These aircraft are used on short-haul routes to Australia, throughout the Pacific and domestically.

NEO stands for Next Engine Option, and is the newer more fuel-efficient jets the airline has been receiving in recent years.

Despite having 32 of the engines on its planes, four spares, and three lease options - the airline is still facing a choke point.

"Essentially, we don't have enough engines," the Group General Manager of Engineering and Maintenance at Air NZ, Brett Daley explained to Stuff Travel.

"The scheduled removal of engines and usual non-scheduled removals are all coming together at the same time for every operator around the world."

That's led to an "escalation" of demand for spare engines, which Pratt and Whitney can't keep up with.

"What we thought would be a problem with us until June, July is probably going to be with us to the end of the year," Daley said.

Air NZ has therefore made the decision to ground two of its newest planes, including a brand new domestically configured A321neo. It is taking engines off the grounded planes - which fly domestically - and putting them on internationally configured aircraft, which gives them more options on where they can be deployed.

"We're really fortunate that because we've proactively managed this, that we're only seeing two airframes impacted," Daly said.

Other airlines are facing larger groundings, with around 100 planes impacted around the world across 28 airlines.

The changes mean around 4000 people won't be able to fly on their planned day, and of them, around 300 people flying to places like Niue or Noumea - with limited frequency - will be impacted by having their flights changed by two days.

The airline's General Manager of Shorthaul, Jeremy O'Brien, says there is a "really good discussion around a potential refund" for customers who have their plans disrupted by a day or two and miss time-bound events like a wedding. O'Brien said it will be working with the most impacted customers closely.

However, of the 147,000 people impacted, 143,000 are within the same day and a majority of those are within 60 to 90 minutes, he explained. Customers will be alerted via email and the Air NZ app, and be able to accept or make changes there.

The reason for the schedule changes is so that planners can "juggle aircraft type and the routes that they're flying in order to backfill as much of the capacity that was impacted by having these two aircraft on the ground" said O'Brien.

"Although there will be some inconvenience for customers, and we apologise upfront for that, the majority [of passengers impacted] will still get to fly within 60 to 90 minutes or on the same day. And that's because we've been able to juggle those aircraft with the other capacity.

The airline started letting customers know about the schedule changes on Monday, and will continue alerting customers over the next 10 days.

The airline is looking at all options to minimise any further description.

"We're also in active discussions with short-term lessors around potential other aircraft," O'Brien said.

Daley explained this issue is very different from the turbulent time Air NZ faced with Rolls-Royce engines from 2017 to 2019, which grounded some of its larger 787 fleet.

The big difference, he said, is Rolls-Royce was a "technical" issue, whereas this is now an "availability issue".

"I guess in terms of severity and complexity, it's relatively minor compared to the Rolls-Royce at this point - we don't want to jump ahead to say that it's going to be like that for the remainder of the year."

Aside from looking into leasing extra engines and planes, the airline is also considering whether it can use the Wamos Air plane its currently using to fly its Auckland to Perth route for other services, which might free up some of its fleet.

"We're looking at basically pulling all the levers we possibly can to get engines back in service."

Advice for customers

A spokesperson for the airline said passengers with flights booked this year do not need to proactively get in touch.

"There is no need for customers to contact Air New Zealand to check their booking. Affected customers will be contacted directly by Air New Zealand either by email or through the Air New Zealand app. If passengers have booked through a travel agent, their agent will contact them directly," the spokesperson said.

* This story originally appeared on Stuff.