A Swiss International Air Lines Airbus A319 carrying 103 passengers and five crew members was about five nautical miles (9.2 kilometres) from Kloten’s runway 14 when a drone suddenly appeared 20 metres above the plane.
No one was injured in the incident but the Swiss Transportation Safety Investigation Board is now investigating.
Under Swiss drone laws, it is illegal to fly a drone weighing 500 grams or more within five kilometres of landing fields and heliports without prior permission.
The Swiss Federal Aviation Office (BAZL) also told The Local on Thursday that the weight restriction would be lowered to 250 grams in future as the European Union rolls out new regulations around drone use.
For airports and heliports with air traffic control systems there are also designated control zones where drones can only fly to a maximum height of 150 metres above the ground.
The control zone around Zurich airport is marked in blue above. Image: swisstopo; FOCA
On Wednesday, a BAZL spokesperson said it would be next to impossible to identify the person operating the drone in the incident in late September because it would have been controlled from a distance via camera.
The spokesperson said that the amount of potential damage in such an incident depended on the size of the drone. He added that a collision between a plane and a drone might not lead to a crash but could still results in millions of francs in damage.
In 2016, the Swiss Federal Aviation Office (BAZL) put out a map showing where drone operators can and can't fly in the wake of a series of incident involving aircraft and drones.
But earlier this year, Swiss airlines safety boss Philipp Spörli told Zurich daily the Tages Anzeiger that many people flying drones were unaware of the rules.
BAZL is currently creating an electronic register of drone operators while authorities at Zurich airport are calling for training courses to be run.