Why are there long queues at Australian airports - and what is being done to fix it?

Long queues spilling out of Australian airport terminals are continuing to make the news.

Airport chiefs say chaotic scenes at departure halls have been fuelled by a range of factors set to come to a head over Easter and the Anzac day holiday.

Security companies have been desperately sourcing more staff, health departments have relaxed isolation rules to reduce absenteeism, and airline bosses have backtracked after appearing to blame travellers for long delays.

So why are Australia's airports in such a state of chaos at the moment? And will it get worse before it gets better?

The long queues at Australian airports - particularly domestic departure halls - rose to prominence last week, but the aviation industry was aware of potential issues well before then.

On 28 March, Sydney airport warned domestic travellers to arrive two hours before their flight's departure time - up from the traditionally recommended one hour. The airport predicted it would be busier than any time in the preceding two years as people started travelling following Covid lockdowns and disruptions.

At the same time, it was down staff after struggling to recruit workers following the lengthy pandemic-related shutdowns.

The Sydney airport chief executive, Geoff Culbert, told ABC TV on Tuesday "on any given day we're operating at 60% of pre-Covid staffing levels dealing with 90% of pre-Covid passenger levels and the maths leads you to where you are".

He insisted the airport was recruiting back in December "but we just can't get the people into the roles".

Queues at security checkpoints - which travellers must go through after checking their baggage - have been the source of the delays.

Certis, the private company that Sydney airport contracts to provide passenger security services, was working in advance to rebuild a workforce reduced during the pandemic.

The recent spike in Covid cases and an associated rise in staff being forced to isolate - whether as cases or close contacts - further complicates matters.

Security and airport staff who are household contacts of a Covid case had - like the general population - been required to isolate for seven days, drastically reducing the ability of airports and airlines to maintain already depleted workforces.

At Sydney, security queues have become so bad that passengers have reported missing connecting international flights when transiting between terminals.

At times, only a fraction of the security checkpoint lanes have been open.

Even with passengers arriving two hours before flights, long queues have been forming before 5am - well before the airport's curfew lifts. Back office, IT and retail staff have been moved to the departure hall to comb through crowds to prioritise passengers at risk of missing their flight.

No. Sydney airport appears to have experienced the most significant delays but travellers at other major airports, including Melbourne and Brisbane, have also been hit with long delays at the departure gates.

Warnings that domestic travellers should arrive two hours before their flight's scheduled departure have also been issued to travellers at these airports.

Sydney airport has warned the delays will get worse before they get better. It expects this Thursday, 14 April, to be its busiest day since the start of the pandemic with about 80,000 passengers passing through the domestic terminal. Brisbane is expecting 50,000 visitors on Thursday.

Pleas for passengers to arrive two hours before their flight's departure have eased queues at certain times in recent days, but pressure points remain.

Since the chaos began last week, the Victorian and New South Wales health departments have tweaked their Covid isolation rules for household contacts of positive cases.

Air transport service staff - including security personnel at airports - are now recognised as critical workers. That means they are exempt from the requirement to isolate for seven days if a close contact of a case - provided they are symptom-free.

Workers whose absence would pose a high risk of disruption as determined by their employer qualify for the new rule. However, they must travel directly from their home to work, must wear a mask at all times, and are required to frequently test themselves for Covid over the course of what would have been their isolation period.

This isn't easy to answer.

Assessing the implications for Covid transmission, Peter Collignon, a professor of infectious diseases at the Australian National University, believes it is a sensible tradeoff given Australia has achieved widespread Covid vaccination.

He says health departments easing the rules appear to recognise that a masked, asymptomatic close contact worker poses a transmission threat that is equal to - or outweighed by - a situation in which hundreds of potentially Covid-positive travellers are standing in close proximity in a departure hall for hours on end.

"It is a critical function to allow flying, so it's not unreasonable," Collignon says. "Crucially, the isolation rules that have been forcing the standstill at the airports can perversely increase the infection rate, as they're causing people to line up together for hours in a poorly ventilated room."

Baggage handlers and other ground staff have also been affected by the same structural shortages and Covid issues that have hit the security workforce.

At Sydney airport, wait times for baggage have ballooned, with officials acknowledging that passengers in the international terminal have had to wait up to one hour after landing for their bags to be taken off the plane and put on luggage carousels

While security and airport staff shortages have been identified as the main problem affecting the queues at airports, the industry says there are other factors at play.

The Qantas chief executive, Alan Joyce, was forced to clarify comments he made on Friday that passengers were "not match fit" and that those forgetting to remove laptops and aerosols from their bags at the security check are contributing to the delays.

"Just to be clear, I'm not 'blaming' passengers," Joyce said later. "Of course, it's not their fault."

In his warning in late March, Sydney airport's general manager of operations, Greg Hay, made similar comments about travellers causing delays at screening points.

But shortages have plagued the aviation industry throughout the pandemic.

Qantas shed thousands of staff and outsourced ground crews in a decision that was challenged in court. Unions have criticised the airline over the effect of its outsourcing and the expectations placed on fewer staff members.

Pilots and aircrews are also in short supply. This week, Qantas issued an urgent plea for pilots to fly three international flights and a number of domestic flights scheduled for the coming days. The airline has also apologised to customers who have faced long wait times with its call centres trying to reorganise flights that had been cancelled.