In order to fly a SUA in a congested area, SUA operators must establish safety and operational control measures that prevent the SUA from endangering the general public. Operators are advised to ensure that their existing risk assessment and operating procedures address the enhanced measures required for congested areas.
The procedures should address all relevant aspects of the congested areas they intend to operate within, taking into account any special circumstances or local conditions. Such measures may include but not be limited to:
Segregation. Segregating the activities from public interference by placing physical barriers and cordons, or using other built/natural features that effectively separate the SUA operation from the general public.
Crowd control. Marshalling or other active crowd control measures that restrict access to the area within which the SUA is operating.
Utilisation of other agencies. Liaising with the Police, local authorities and other controlling agencies/organisation to gain official road closures, traffic cessation or site access restrictions.
Note: These measures should ideally be proportionate to the risk posed by the SUA, bearing in mind the limited flight times and size and weight of the aircraft. Temporary restrictions may suffice in some cases. Restrictions that would be suitable for a full-size aircraft such as a helicopter in most cases would not be applicable to a SUA.
Wind and turbulence. Taking account of changes of wind strength and direction at varying heights above the surface. Windshear, ‘rotor’ and ‘curl-over’ effects may be present at any point on the planned flight path caused by interactions between buildings and strong winds or when transitioning from flight over a land to a water surface.
Radio Frequency (RF) interference. Pilots should take account of the possible reduction in operating range in an urban environment due to the heavy use of communications (mobile telephone, WiFi etc.) equipment and other sources of electromagnetic spectrum/RF interference. Mitigation for the consequences of weak or lost GPS signal due to masking by buildings should be considered along with the general RF saturation level. The use of a spectrum analyser is recommended to assist in assessing the level of local electromagnetic and RF congestion in the 2.4 GHz or 35 MHz frequency range.
Emergency procedures. SUA emergency procedures planned to be implemented during controller/transmitter/loss of GPS guidance failure modes should be able to be put into effect without breaching the minimum separation distances or flying directly overhead persons/vehicles. An automatic ‘Return-to-Base’ feature should not cause a hazard to anyone off the nominal flight path; this may limit the SUA to mainly vertical flight paths directly above the launch point.
Test flights. It is desirable to conduct limited test flights (hover controllability check) and other systems tests at the launch point before committing to the full flight profile. The integration and correct set-up of the camera and gimballed-mount should also be checked at this time to avoid unnecessary calibration flights.
The procedures and limitations on the use of the SUA that will be used to establish these control measures should be stated in the SUA operators’ operations manual.