External risk factors influence the project objectives, especially project scheduling. Some risks may occur frequently but have low impact, while others may have both high frequency and high severity. The linkage between risk frequency and impact needs to be assessed to understand the significance of a risk variable. This study was aimed to examine the significance of risk related to the probability of occurrence and the magnitude of impact on the project schedule. The study focused on external risk factors (sociopolitical, government policy, natural disasters, and monetary). Survey questionnaires were sent to 20 targeted contractor companies in the area of Aceh Province, Indonesia with a response rate of (60%). Using Risk Importance Index (RII), the significant risk variables that hindered the achievement of project achievement in Period I have been identified as follows: cultural conditions and local customs near project site (K4), social issues/surrounding environment (K5), increased fuel prices (L4), uncertain weather conditions (M1). In addition, the emergence of L4 variable in Period I was due to temporary security conditions, while in Period II due to the conditions of supply and demand. The results of this study are intended to contribute to the application of risk to practitioners and governments.