There are several synonyms for the phrase "long plane" which can be used in different contexts. If you're referring to a flight or journey, estimations like "extended travel", "lengthy trip" or "prolonged expedition" may be more suitable choices. Alternatively, if you're describing a straight, narrow or elongated object, you might use phrases like "lengthened shape", "extended form" or "elongated construction". In certain cases, the term "long plane" could also be replaced by more specific language depending on the object in question; for example, a "stretch of pavement" could refer to a long plane surface such as a road or runway.