Name the original air date for ai% for 83
CREATE TABLE "table1_18012738_1" (
  "story_no" text,
  "episode" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "uk_viewers_million" text,
  "ai_pct" real,
  "original_air_date" text,
  "production_code" text
);
SELECT "original_air_date" FROM "table1_18012738_1" WHERE "ai_pct"=83;