In June 2024, Aerial Defence Ltd deployed a CUAS (Counter Uncrewed Aircraft System) sensor in the Borehamwood area of Hertfordshire, UK, for a two-week monitoring period.

The deployment and monitoring location included a number of key sites of interest, including the Elstree Aerodrome Flight Restriction Zone (FRZ) EGR131A and Runway Protection Zones (RPZ) EGR131B and EGR131C. This volume of restricted airspace expands two nautical miles from the centre of the Elstree Aerodrome from surface to 2000ft. It has a perimeter of 18.6 miles and an area of 17.8 sq. miles. The airfield is one of the busiest in this area with constant in and outbound light aircraft and helicopter flights.

These were the findings:

  • 331 flights were observed, with 226 detected flights attributed to drones weighing below 250grams.
  • 67 flights were detected within the Flight Restriction Zone (FRZ), of which 57 were unauthorised.
  • 88% of drones flown within the FRZ were under 250 grams.
  • The highest unauthorised flight within the FRZ reached 1,392ft (424m) — over 3.5 times the legal limit.
  • In total, of the 331 detections, 43% of all aircraft flown were above the legal limit of 400ft.
  • Of those above 400ft, more than 50% were between 500ft and 1000ft .
  • With flights above 1000ft posing perhaps the greatest risk, the highest drone was recorded at 4,437ft.  Critically, 32.27% of the flights which flew above 400ft exceeded 1000ft.

According to the UK AirProx Board, there were 11 reports of drones near aircraft or airfields across the UK until May 2024. In just two weeks within ONE FRZ, 57 unauthorised flights were detected.

Throughout the two-week monitoring period, only 38.97% of drones were considered as being flown legally, with the remaining 61.03% therefore considered to have been flown illegally.

Whilst these figures represent potential offences relating to the way the drones were flown and therefore breaches of the Air Navigation Order, they do not highlight those flights which were detected and by their nature, could indicate drone enabled crimes, such as hostile reconnaissance and other highly suspicious activities.

It is clear that these figures are not isolated incidents and are likely representative of broader trends beyond just Borehamwood.

Is YOUR airspace as secure as you think?