Difference between 1013hPa and QNH (1003hPa) = 10hPa x 27ft = 270ft.
The airfield is at a pressure altitude of 2,270ft.
Aircraft needs to climb 5,000 - 2,270 = 2,730ft to reach FL50.
At 1,000ft per minute this will take 2.73minutes.
Groundspeed = 100 - 20 = 80kts.
In 2.73 minutes at a groundspeed of 80 kts the aircraft will cover a
distance of 3.6nm.