***** NOT A TEACHER *****
I know that I am being too sensitive, but as soon as I read WinWin's question, I said to myself: Considering all the recent airplane tragedies (which Tedmc also referred to in his post), it might be a good idea NOT to mention "landings."
In fact, it might be a good idea NOT to refer to the flight itself in any way.
Of course, you have to say something to your boss. So maybe it should refer to his recent visit ("We hope to see you again very soon. We really enjoyed your visit.") or to his destination ("I'm sure the home office [in London] will find your findings very helpful." / "I hear that the weather in London is really nice at this time of the year." (Say anything that will take his mind off the actual flight.)