SELECT "Fleet series" FROM table_78251 WHERE "Quantity" = '5'
Name the fleet series with a quantity of 5
CREATE TABLE table_78251 (
    "Year" real,
    "Manufacturer" text,
    "Model" text,
    "Length (ft.)" text,
    "Fuel or Propulsion" text,
    "Fleet series" text,
    "Quantity" real
)