CREATE TABLE table_204_710 (id DECIMAL, "model" TEXT, "origin" TEXT, "type" TEXT, "versions" TEXT, "in service" TEXT, "notes" TEXT)

what type of aircraft has the longest listed service record ?
SELECT "type" FROM table_204_710 ORDER BY "in service" DESC LIMIT 1
SELECT "type" FROM "table_204_710" ORDER BY "in service" DESC NULLS LAST LIMIT 1