The United offloading saga has set a precedent for the industry - on how not to handle passengers. As a result the lawyer for a man who suffered a concussion and lost two teeth when he was dragged off a United Express flight hopes the 69-year-old becomes "a poster child" for the mistreatment passengers suffer at the hands of the airline industry.

Associate Press reports, Attorney Thomas Demetrio indicated on Thursday Dr David Dao will sue United and the city of Chicago, which employs the officers who pulled Dao off Sunday's Louisville-bound flight.

In widely shared cellphone video, Dao is dragged down the aisle on his back, his face bloody.

Demetrio said the video showed an extraordinary instance of something that happens too routinely: Airlines overbooking flights then bumping paying customers. He says it exposed a culture in which airlines have "bullied" passengers.

United has apologized and says it won't happen again - but not before social media heavily berated the airline.

What should South African passengers know about overbooking and offloading on flights?

While it is common practice across the globe for airlines to overbook flights, most passengers don't entirely understand the practice.

According to the Head of the Airlines Association of Southern Africa Chris Zwiegenthal, the overall aim is so that airlines can maximise revenue around load factors as well as avoid having empty seats that are either not used due to no-shows as well as being able to accommodate passengers on standby who urgently need to travel.

While policies vary from airline to airline – allowances are made for the offloading and overbooking practice in South Africa in the Consumer Protection Act in article 47, detailing parameters of due process that should involve prior notification and compensation where possible.

Local airlines say that while it seldom happens, the conduct is outlined in their individual conditions of carriage, which explains the due steps around notification and compensation policies of each particular airline.

FlySafair spokesperson Kirby Gordon says, "It very seldom happens but when it does, our policy is that we load all passengers in the order that they check-in. If there are extra and the flight is full then we offer the last passengers who are unable to board a seat on the next available flight and R1 000 in cash, or alternately a full refund."

Zwiegenthal states these compensation requirements vary quite extensively from airline to airline, and passengers should familiarise themselves with it.

It can either be a voluntary or involuntary process, when it comes to offloading

Voluntary means the passenger is offered the option to travel at a later stage. When it is possible and suitable for the passenger, with compensation of a reduced ticket price making it even more worthwhile - ultimately the process is smooth.

However involuntary is never ideal, as was the case with the United passenger.

Zweigenthal says airlines have very sophisticated booking systems that usually allow them to make an informed estimation.

As an example, booking patterns would show a 6 to 7% of no shows on certain flight routes at certain flight times - this then allows the airline to overbook to less than that percentage as part of its revenue management systems.

"I must emphasises this process to determine overbooking changes from airline to airline, including how far they prepared to overbook. The methodology mostly used on the cheaper tickets in economy, rather than business class - as the airlines are looking to maximise revenue and give passengers the opportunity to fly if they really need to.

This would usually avoid the irritation of empty seats when you desperately need one, says Zweitgenthal.

Preferably offloading should be voluntary

He says the United instance is very regrettable and reports indicate there must have been a system issue.

“Preferably offloading should be a voluntary process,” says Zweigenthal, "Any offloading should take place before the passenger even gets near the plane."

According to Zweigenthal airlines very rarely want to antagonise or disrupt the travel plans of their passengers and he knows of no known instance locally, similar to the United Airline incident.

Traveller24’s advice is to know you conditions of carriage and be timeous in your arrival and check-in processes so as not to get into any compromising situations. While involuntary offloading might not be frequent, delays or cancellations are.

- Traveller24