Reducing APD would no doubt have a positive effect on the bottom line for Flybe (and others).
For example, and feel free to correct me if I'm working this out wrong; lets say Flybe's average load factor at CWL is 75% (66 passengers), and lets say 10 of them are under 16 so not eligible to pay APD, so on average 56 passengers per flight paying £13 APD.
Each aircraft doing 6 sectors (3 return flights) per day.
56 passengers x£13 = £728 per flight
728 x 6 sectors = £4368 per aircraft per day
£4368 x 3 based aircraft = £13104 in APD alone per day.
Multiply that by 363 days of full travel per year = £4,756,752
Note: This is based on E75 capacity.
It's worth noting that the government is forecasting to earn 3.5Billion from APD in 2018/19