Hallo Rachel....By coincidence a contact of mine raised the question of the crew-list for the Chamberlain flights last week and puzzingly neither Pelly or Seabrook-Smith appear on the official list for the second flight to/from Cologne which is where the photo was taken, but as the list has 4 crew on the main aircraft and only 2 on the back-up aircraft on each trip it is quite possible there were 'extras' . I see your grandfather wrote some articles in Aeroplane Monthly in the 1970s which I have and will look at today. I'll send a you a Private Message'...Mick