When United Airlines flight UA90 took off from Newark Airport bound for Tel Aviv on January 20, 2022, all seemed normal. But then, a couple of economy class passengers decided to lift themselves up to where they truly belong, which happened to be business class.

Why not, they reasoned? The seats were empty, it's a long overnight flight, they could get a good night's kip in the fully-reclining seats, wake to a splendid breakfast and land at Tel Aviv relaxed and refreshed.

The cabin crew did not see it that way, pointing out that they had paid for economy seats and that's where they belonged. The arguments went back and forth, but negotiations stalled and a standoff ensued.

Both sides refused to budge, and so the captain did a loop over Nova Scotia and landed the aircraft back at Newark, two hours after it took off.

Not only did the trespassers not get to keep their seats, they were fingered as the reason the passengers were spending the night in a hotel somewhere near Newark Airport instead of meeting friends and loved ones in Tel Aviv.

And when the aircraft landed it was met by police who marched the offenders off the aircraft and into custody. Cue the walk of shame, except the miscreants probably missed out on the shame gene.

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Why don't airlines upgrade you when seats are empty? Flight turns back after economy passengers upgrade themselves to business class

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The cheapest return economy seat aboard a UA flight from Newark to Tel Aviv in April costs $US775. The cheapest business-class seat on those same flights costs $US2735. What right-minded person thinks they can upgrade themselves from a cheap seat to a much better one that costs four times as much?

If you have a ticket to the Australian Open and find yourself sitting up in the gods, you can't wander down to a corporate box and plonk yourself down just because there happens to be a few empty seats there.

Think you'll get away with this? A sneaky poach in the dead of night, after the meal service when the business cabin is hushed and dark? Blanket out, swiftly over head and feign sleep? Nope! Because cabin crew are onto you.

Once, flying premium economy aboard Singapore Airlines, I used the business class toilet since premium economy has no dedicated toilets and all the economy ones were occupied. I copped a raised eyebrow and wagging finger from the crew, which is about as severe a takedown as you're ever likely to get on a Singapore Air flight.

Airlines do not upgrade economy passengers just because there happen to be empty seats in business or first. What they might do if there are high-status passengers flying economy is cut them out from the herd and give them a better seat. There is a pecking order and those who have demonstrated their loyalty to the airline by flying lots and acquiring heaps of status credits are first in line.

You can sometimes buy an upgrade at the check-in counter. It's probably going to cost less than the difference between the economy seat you paid for and a business-class seat but there are no sweet bargain-basement deals here.

I once got upgraded that way on a flight from Bangkok to Sydney but it cost $800 on someone else's expense account. If it was my call I would have stuck it out in economy and saved the cash.

That calls for an operational upgrade, an op up in plane speaking. Again it's the platinum or gold flyers who get the nod. If there aren't enough of them around, the airline might give the call to those among the passengers who have paid the highest price for their ticket.

Why weren't those two self-upgraders aboard flight UA90 smarter? There were just 123 passengers on board. That means a heap of empty seats aboard the 787-1000, which easily accommodates 300. It doesn't take major smarts to figure out they could have moved to an empty row in economy, scored three seats across, laid down and goodnight. And flight crew would not have said a single word.

Because that's one of the things you can get away with. If you happen to find yourself in an economy cabin with empty rows while yours is not, why not make yourself a little more comfortable? Timing is crucial, and you need to get out of the blocks as soon as the doors close. The aircraft is fully loaded so no chance off encroaching on someone else's legitimate seat and crew are fully occupied with other more important things so they won't bother you. Delay too long and you might get gazumped by, well - me for example.

When you do this, do not take the aisle seat. That leaves the door open for another passenger to come along and take the opposite aisle seat. Take the middle seat or, if it's a row of four seats, the seat second in from the aisle and spread your goods and chattels liberally on the other centre seat, thus establishing your property rights beyond all reasonable doubt. The rules can be bent, but breaking them comes at a cost.

See also: Airline review: Business class on Qantas' new non-stop flight to London

See also: What are airline status points and how can you earn them without flying?