The paper is about the study of building a Reliability Program for the Leonardo AW139 Fleet of a start-up company that is based in the Middle East. The start-up helicopter company started its operations in 2018 with an initial fleet of 2 AW139 and grew to 10 helicopters in 2021 and is expected to have a total of 30 to 40 AW139 in the next 5 years. All helicopters purchased were brand new except for the first two helicopters that were leased from another company, hence, the initial maintenance did not require a reliability program. However, in the last 3 years, the fleet slowly accumulated system, component and/or structural defects and findings that prompted the Continuous Airworthiness Department to build a reliability program in anticipation and preparation to revise and update the maintenance program, as applicable, for the upcoming aircraft. A historical data from 2020 to 2022 was collected and computed for the standard deviation multiplied by 3 for the aircraft system, component per ATA chapter and structural defect's upper control limit or alert level. This will be determined and analyzed per 1000 flying hours to provide a reliability report, mitigation and corrective action to improve the maintenance reliability of the fleet. Moreover, the study will research for other monitoring and/or data collection apart from the current practice to be able to obtain more data and have a better projection in the reliability report that will also cover the on-time-performance of the aircraft. Fish-bone diagram and FMEA will be used to determine the root cause and provide potential solutions based on the trend monitoring of the defect rate. Apart from the study, the other objective of the paper is to present it to the management of the start-up helicopter company and be able to utilize this as basis or foundation of the actual Reliability Program of the company.