Abstract: An accurate definition of helicopter alert time without maintenance (tal) is given. Then, the tal is studied by using the concept of Q-percentile life. A general method is derived for calculating the tal under the presupposition that alert failure density functions of the relevant subsystems or components are known and two formulas are obtained. Finally, the basis to find out relevant subsystems or components and the way to realize tal are also presented.

Key words: helicopter, reliability, alert time without maintenance