Australia’s air traffic controller provider said it may need months to address worker shortages at Sydney Airport, following weeks of staffing problems and mistakes on the tarmac that have raised concerns about safety.

Airservices Australia plans to shore up the roster at Sydney by March, and avoid the flight delays that have plagued travelers in recent weeks, Deputy Chief Executive Officer Peter Curran said at a parliamentary hearing in Canberra on Friday. Airservices aims to add daily on-call shifts to the workforce, reducing disruptions when controllers call in sick or have unplanned absences, he said.

“It’s not an iron-clad model, but it certainly reduces the likelihood of the sorts of issues that we’re having today,” Curran said.

ALSO READ: Sydney air traffic controllers warn of grave safety concerns

At least six near misses and other incidents at Sydney since late July have shone a spotlight on a persistent shortfall of air traffic controllers at Australia’s biggest aviation hub. The Australian Transport Safety Bureau is investigating all six events.

Qantas Airways Ltd Chief Executive Officer Vanessa Hudson made a rare intervention last month when she called for the shortages of controllers to be fixed, after around 60,000 passengers were affected by flight delays in July alone.

Curran said Airservices employs 49 air traffic controllers at Sydney Airport. The control tower needs 41 staff in order to be operational so it’s “very difficult to recover” when there’s short-term illness, he said. For instance, there were significant flight delays at Sydney on Friday because just one controller became unavailable, he said.

READ MORE: Crew member injured in near miss between planes on Sydney Airport runway

The recent incidents at Sydney Airport include a passenger jet aborting its takeoff because there was a plane in its path, and a taxiing aircraft slamming on its brakes to avoid colliding with another jet.