The phrase "is on the scene" is commonly used to describe a person or group's arrival at a particular location or event. However, there are many synonyms that can be used instead of this phrase. For example, you could say that someone has "arrived," "appeared," "shown up," "made an entrance," or "came on the scene." Alternatively, you could use more specific language to describe a person's actions or presence, such as "started investigating," "began surveying," or "commenced assessing." These alternatives can help you vary your language and make your writing more interesting and engaging.