Scrapping Air Passenger Duty (Tax) and making it Per Plane Duty (Tax) will no doubt increase prices.
The Airlines will spread the cost on 50 or so seats and pocket the rest. This will cover it if they do not sell more tickets.
They are also putting this on Freight Planes. Products, Mail and Goods that need to be flown in and out will cost more.
Nothing like 'Taxes fair for all' slogans 'that put money back in your pocket'