Here's how it is in the UK.... On 13th March 2019 the Flight Restrictions Zones (FRZ) around airfields were increased from 1km to 2 or 2.5 nautical miles, plus a 5km x 1km strip at each end of the runway. The details for each airfield can be found here (click on the icon at top left of the map):
Airfield restrictions - Dronesafe I have attached a screenshot from London City Airport, which is airfield the OP was referring to.
"It is illegal to fly any drone at any time within these restricted zones unless you have permission from air traffic control at the airport". On the 25th April, NATS (National Air Traffic Services) introduced a new system for requesting permission instead of calling the ATC - the new Airspace User Portal:
Home | NATS AUP.
You use the portal to get permission in principle to fly in the FRZ at your requested location (within a 500m radius). This permission can be for up to 12 months. Then each time you want to fly you use the portal to get permission from the airport's air traffic control tower. That's the theory. In practice only 6 airfields are using the portal so far. For the rest, you still have to call the ATC. Having got permission you can then go through the unlocking process on the DJI Go 4 app and your Spark.
I have done this a couple of times to fly 2.5km north of Bristol airport, with no problems. I did ask ATC whether I needed to get permission if I was flying in a field below the treeline. The answer was yes, if there was any chance they might see the drone. The processes all work so go along with them and stay legal. ATC were very friendly and helpful.
The OP said he was 5km from the airfield. As long as that wasn't in line with the ends of the runway, it's further than the 2NM limit (3.7km) so is legal (below 400 feet). It will still be within the authorisation zone on the DJI map, so still requires acceptance of responsibility.
