What is the name of the episode originally aired on September 29, 1999?
CREATE TABLE "table1_18646432_4" (
  "series_num" text,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "prod_code" real
);
SELECT "title" FROM "table1_18646432_4" WHERE "original_air_date"='September 29, 1999';