"...revenue per pax is falling..." is an interesting term. Airports are forgetting why they exist. They are there to provide a service to airlines and in turn, the passengers of these airlines. They are not hotels, shopping centres, restaurants, retailers, hairdressers etc. Unfortunately their greed knows no bounds and they chisel, pry and prise every bloody cent out of their victims, because that's what they are. Until they fully understand why they exist they will continue to lose revenue. Take Schiphol. I'm convinced this place has a Flight Prevention Department. They make sure flights do not leave on time with CDM (a complete bloody joke) and flights do not arrive on time by reducing runway availability to appease a handful of tree huggers and moaners. The result is late running flights and passengers rushing from one place to another to catch a flight. Pissed off, rushing passengers are not good shoppers!
No doubt millions will be spent of surveys asking the wrong questions in order to find out what they already know. Then MBA'ed consultants will be commissioned and that will result in bonuses all round and even more shops. All the time the requirements of airlines and their passengers will be ignored. And the revenue will continue to decrease. The modern world we live in!
PM