Question: What is the original air date of the episode directed by Ian Barry and written by Philip Dalkin?
Schema: create table table_18712423_3 (original_air_date varchar, directed_by varchar, written_by varchar, PRIMARY KEY (original_air_date))
SQL: select original_air_date from table_18712423_3 where directed_by = "ian barry" and written_by = "philip dalkin"