More on Yverdon here.
I decided when I wanted to end Cabin Pressure in between the Christmas special (M) and the start of series 3 (N). At that point I had written two series and a special - 13 episodes - and I noticed that if I could get the BBC to give me the same again, that would take me to the end of the alphabet. So, all of series 3 and 4 were written with some of the events of Yverdon and Zurich in mind. Not that that informed every line, or even every episode, but overall, I knew my job was to get Martin to the point where he could - with great difficulty, and by an extraordinary effort, pass a job interview at a 'proper' airline'… and poor old Douglas to the point where he knows exactly how Martin felt in Abu Dhabi. Meanwhile, Carolyn was heading to the point where she was resigned, if not cheerful, about giving up MJN; and indeed prepared to encourage Martin to leave it - but with another, Herc-shaped dilemma to solve instead.
I like Oskar's line about having tuned out for Martin's big speech. I knew the interview had to climax with one, because both we and Martin needed it, but I was never quite comfortable with it clinching the job for him, because a) it felt a bit of a Hollywood ending, and b) that isn't how airline recruiting works. So, I retuned the character of Oskar, who previously had just been another interviewer, there throughout, and pretty much interchangeable with Elise, into an unpredictable but shrewd CEO who had the power to shortcut the whole process and hire Martin on the spot. But, as he says, he doesn't do that because of the 'hero speech' - he's already made up his mind by then. And the things that get Martin the job offer (apart from his ability and willingness to learn the manuals, which he's always had) are all things he's learned to do at MJN. Plus, his getting Oskar to stay in the room. Which again, I don't think he could have done before he met Douglas, or Carolyn.
In other words, the journey to Yverdon was to get the main characters to the point where Martin could plausibly say 'I would like you to give me ten minutes to change your mind'; Douglas could plausibly say 'I am the supreme commander of this vessel', and Carolyn could plausibly say 'It's only money.'
Meanwhile, Arthur... eats a dragon-fruit. Well, some characters are more prone to complex emotional development than others. But Arthur does have perhaps the key line in the whole episode, near the beginning:
'Good luck, Skip! I hope you get the job! But I also hope you stay with us! So overall, I hope, er ... I don’t know what I hope!'
My aim was to bring the audience to the same point, especially once Martin gets the offer. If he turns it down, he's taking a backward step, away from financial security, the job he's always wanted, and the most promising romance of his life. But if he takes it, he's not only leaving a life he now enjoys with his closest friends, but forcing the closure of MJN, and thus surely changing all three of their lives for the worse. So, what's he to do? What do you hope he does? Do you know what you hope? Well, almost two years later, get ready to find out...
3. MARTIN: I'm afraid I'm too much of a perfectionist. I try too hard to do every aspect of my job really well.
4. DEROCHE: That's your greatest weakness?
5. MARTIN: Yes.
6. DEROCHE: So, if you joined us here, how would you work on improving it?
7. MARTIN: Well ... I suppose ... I would try to do everything more ... badly.