The nation's air safety boss has questioned why it took four days for another safety incident at Sydney Airport to be reported to investigators.Air Transport Safety Bureau (ATSB) chief commissioner Angus Mitchell told the ABC he was only notified of Sunday's incident about lunchtime on Thursday.The most recent incident last Sunday involved two planes more than kilometre away crossing the same runway ahead of take-off.Air Services Australia said the two aircraft were never in close proximity and was working with the ATSB to investigate the incident."The two aircraft didn't come within really probably around a thousand metres of each other For it to progress through to an actual accident, multiple things need to go wrong."Equally in this one, this latest one that was reported to us, a traffic control cancelled the take-off clearance around the same time as the pilot on board realise there was a potential conflict."It comes after two near-misses at Sydney Airport in the space of a fortnight.The first on July 27 saw a Qantas Link and Qantas flight avoid a collision.The second, also last Sunday about three hours before the latest incident to come to light, saw a Jetstar crew member injured after pilots were forced to slam on the brakes to avoid colliding into a Qatar Airlines flight.Two ground crew involved were stood down and underwent blood and alcohol testing as part of the ATSB investigation.The incidents saw renewed calls for change from the Civil Air, whose president Scott Nugent said there were not enough air traffic controllers in Australia and it was putting pressure on services.The near-misses resulted in Airservices Australia CEO Rob Sharp summoned to Canberra to meet with Transport Minister Catherine King.