Mission Reliability

[natz_aero]

Currently am working in aviation project, till now my aircraft mission hour is 1 hr and the field data collected from various test flights for mission of 1 hr was analysed using Weibull 2 parameter MLE gives the result of Reliability = 0.96.

To meet future demand, mission hour is going to increase 4 hrs, when i estimated reliability through same analysis for mission of 4hrs, it is coming Reliability < 0.86, but the requirement is to maintain reliability of 0.9

Is my approach for estimating reliabiilty of 4hrs(mission time) from the data collected from various test flights with mission of 1 hr is correct or not?

Is there any other relevant method is available?