A random sample of 800 airline passengers is wanted from 100 particular flights leaving Sydney Airport. Assume there are 200 passengers aboard each flight.

A numbered list of all 100 x 200 = 20,000 passengers on these flights was obtained. One passenger was drawn from each set of 20,000/800 = 25 passengers. Randomly choose among the first 25 passengers on the list to start, and then choose every 25th passenger until 800 passengers were obtained.

What type of sampling technique is this?