Thank you all for your advice. I had no issues with my hand luggage for my four IB flights JFK-MAD-NCE, NCE-MAD-JFK but had to be careful. Like other airlines (LH) recently, I received an email before departure saying the flight was full and I could check my hand luggage for free. At JFK, one of the three check in agents was weighing hand luggage. When passengers realized this, some with hang luggage only went directly to the gate if they already had their boarding passes. I removed my laptop and put it in my backpack to make sure I was under 10kg. I was checked in by a different agent who did not weigh the bag. There was no sizer at check in or at the gate. Also no sizers anywhere at MAD in either direction T4 or T4S. During check in at NCE, one agent had a cardboard sizer but I did not see that agent. I think I could have passed the sizer check because it was open at the end to measure the length (56cm), allowing my wheels to stick out.