Almost 50 flights were cancelled at Sydney Airport yesterday, and many more were delayed. This pattern seems to be repeating itself today, with 30 domestic flights already cancelled. Not the ideal way to start the NSW winter school holidays. 

You see, the air traffic control staff are doing this for the safety of the passengers and crew members. For the past few days, an area of high pressure to the west and a tight pressure gradient with a series of troughs crossing the southeast has driven strong WSW winds over southern NSW. 

Figure 1) Mean Sea Level Pressure chart at 10am today (Sat 1st) as shown by ECMWF Fri 12Z. 

Yesterday's sustained westerly winds at Sydney Airport reached up to 39km/h with gusts up to 61km/h. This may not seem like a significant value to us, but for airplanes landing and taking off the north-to-south runways, these types of winds pushing at their sides can be quite a problem. Winds perpendicular to the direction of flight are known as crosswinds. 

Figure 2) A map of wind gusts over Australia at 10pm on Friday the 30th of June as shown by ECMWF Fri 12Z 

In fact, air traffic operations demand that if a crosswind exceeds the speed of 20 knots (approximately 37 km/h) an alternative landing/take off runway should be used. Sydney airport has two north-to-south runways and only one west-to-east runway. Air traffic staff called a switch from the usual north-to-south runways to the west-to-east runway yesterday due to these strong winds, meaning all planes from the domestic and international airports had to share one runway! 

This is what led to long wait times and flight cancellations. The airport now had to manage arrivals and departures of double the number of flights a single runway would allow for. Further, with the change of runway, it simply meant that some planes just couldn't land or take off. The length of the west-to-east runway is not the same as the north-to-south runways, meaning that some planes didn't have enough "run up" length to make a safe take off/landing, resulting in necessary cancellations. 

So let's hand it to our air traffic controllers for putting our safety first. The good news is that the wind is easing and most flights for the rest of the day will likely go ahead as scheduled. So, despite the rocky start to winter break, it seems passengers will be back on their way to their holiday destinations very soon.