I've run the numbers here https://stattrek.com/online-calculator/poisson.aspx https://stattrek.com/online-calculator/poisson.aspx At a weekly probability of 0

I've run the numbers here https://stattrek.com/online-calculator/poisson.aspx https://stattrek.com/online-calculator/poisson.aspx At a weekly probability of 0.04 (2 failures/52 weeks) the probability of 2 failures within a week is 0.077%. The probability of 0 failures in a week is 96%. Accounting or halving of flight frequency it's 0.02% and 98% respectively.