29 April 1967: broadcast of fourth episode of The Faceless Ones. Jamie gets on a Chameleon plane, which is duly captured by the aliens
29 April 1972: broadcast of fourth episode of The Mutants. The Marshal plans to bombard Solos with ionising rockets; Varan and his men prevent him but the Skybase is damaged.
29 April 2006: broadcast of School Reunion. The Tenth Doctor unexpectedly meets Sarah Jane Smith, thirty years on. (Sob!)
29 April 2017: broadcast of Thin Ice. The Doctor accidentally lands himself and Bill in the past, at the final frost fair in 1814. However, something sinister is lurking below the frozen Thames.