External control for orderly movement of aircraft or space vehicles is becoming increasingly important and challenging with the ever increasing traffic density. Lack of proper monitoring, control and coordination will always result in chaos and compromise air safety. This is even more critical when such movement is in three dimensions at comparatively higher speeds in relative limited volumes of airspace in short time frames, all of which are the characteristics of air traffic.

Evolution

The arrival on the scene of unmanned aerial vehicles (UAVs) has basically added another type of aircraft jostling for airspace previously only occupied by manned aircraft. Till recently UAVs were in the exclusive domain of the military. Integration with manned military aircraft traffic was straightforward since both types were controlled by the same entity and UAVs usually flew in restricted military airspace, carried out specific military tasks and their numbers were very few. All this has changed now with the increasing use of UAVs by non-military entities for commercial and recreational activities. India is becoming one of the largest military UAV operators and so the problem of integration is no longer an issue confined to Western nations.

The situation that existed a couple of decades ago was that except for radio controlled models, acquisition of UAVs was limited by high costs outside the reach of private agencies. Manned aircraft require more elaborate support infrastructure and airstrips for fixed-wing operations. Such installations can be monitored and have communication facilities with air traffic control entities. In addition, the control loop has a human interface by way of a pilot who follows instructions of an air traffic control authority.

The Situation Now

Technological advances have made UAVs with capabilities akin to smaller manned aircraft more affordable and so the recent past has seen an exponential growth of privately owned UAVs operating from just about anywhere. Till now their use had been for legitimate activities and operations have generally been within acceptable safety norms. However, this is changing now with irresponsible operators who may have insufficient training, maybe with unlawful intentions and at times malicious intent getting access to this emerging technology, which like all technology, has potential for harm.

The biggest crowd-puller at the Computer Electronics Show in the USA this year were the drones of all flavours, some of them incorporating cutting-edge technology in remote control, automation, robotics and even sensors. Some of these technologies are probably just making their way into military systems! Given the dynamics of market economies, most of these drones would be made available to anyone with deep enough pockets. The implication is that there would be a flood of devices entering regulated airspace and putting in place proper control mechanisms becomes a matter of utmost urgency both for air safety and airspace security. As usual technology has gone ahead of the means to control it.

Problem Areas

UAVs need to be subject to the same norms of control as manned aircraft if they are to share airspace with the latter. It may have been possible to segregate manned and unmanned aircraft; but with UAVs already having performance capabilities similar to manned vehicles and increasingly intruding into the roles of the latter, restricting the ever increasing numbers of UAVs to segregated airspace is not a viable option.

The real problem is regulating the acquisition and operation of large numbers of UAVs of varying capabilities and limitations of both equipment and operators in congested airspace occupied by an increasing number of manned aircraft. Technology exists at the air traffic control level for surveillance, identification and communications. However, the UAV as well as its remote operator sitting at a location distant from both the control centre and the UAV, also need to have compatible equipment. Most importantly communication links have to have much greater redundancies than with manned aircraft for obvious reasons. The danger is not only to the UAV which has no human occupants but far more to manned aircraft in the vicinity and people on the ground.

Manned aircraft operating in controlled airspace invariably have transponders which when interrogated by groundbased secondary surveillance radars give details of aircraft and their position. Primary surveillance radars such as used in air defence systems are not dependent on aircraft transponders for detection. However, civilian air traffic control uses secondary radars dependant on transponders for tracking aircraft. If UAVs are to operate in controlled airspace, such transponders are essential. The smaller UAVs also have small radar cross sections and are more difficult to detect than larger aircraft even when primary radars are available.

UAVs come in various sizes and capabilities. Large platforms are as big as big passenger aircraft and small ones are the size of kites. Operating altitudes extend from the treetops to 20+ km and endurance from ten to 20 minutes to over a day. The smaller ones, flying low at slow speeds are the biggest hazards for manned aircraft especially in the critical take-off and climbout phase and approach and landing phase. While larger UAVs have the payload capability and size to carry transponders and also have redundant communication links, smaller UAVs may not have the capability to carry such equipment. Till such time as miniaturisation advances make this possible, such UAVs will have to be excluded from high traffic density airspace.

Regulations

The existing regulations need modifications not only in India but worldwide. The European Aviation Safety Agency (EASA) had released a paper called ‘A Concept for Operation of Drones’, which is a risk-based approach to regulation of operation of UAVs and addresses integration with manned aircraft. The paper estimated that in 2013 there were nearly 2,500 operators and 114 manufacturers of small UAVs in the category of maximum take-off weights up to 150 kg in the European Union itself and the category of drones of 150 kg plus would see a rapid growth. It was proposed to classify UAVs into three categories of operations and associated regulatory states for civilian operations – Open, Specific and Certified. Very briefly these are described below:

Open: Requires no authorisation by an aviation authority, no airworthiness certification or licences for equipment or operators. But flights are to stay within defined limitations. Flight limitations suggested were visual contact with maximum 500 metres distance, 150 metres altitude and outside restricted/controlled airspace. Industry standards of safety of equipment to be applied with toys of less than 500 gm exempt.

Specific: This is one step above the operations of the Open category and is subject to certification by the National Aviation Authority for the specific role. Operational procedures would have to be approved and in some cases and roles licensing would be required.

Certified: Here the operation complexity and risk are akin to normal manned aviation with comparable regulations in force. Integration into non-restricted airspace would be subject to a safety assessment of the air traffic services provider. Licensing of equipment and pilots would be required.

The US Federal Aviation Administration (FAA) had also issued a road map as early as in 2013 for UAV integration into the National Airspace System. This goes into quite a bit of detail about all aspects including licensing, communications, training, etc.

Summary

The general trend is to treat operation of UAVs with performance akin to light manned aircraft on par with manned aircraft of similar capabilities with relevant training, inspection, certification and controls in place. National security issues have also to be addressed. The limitations of UAVs because of the need for a data link for control of aircraft leading to delays in responding to air traffic control instructions, manoeuvring to avoid conflicting traffic or for dealing with emergencies will have to be kept in mind when operating alongside manned aircraft. A level of “sense and avoid capability” for collision avoidance akin to the “see and avoid capability” of manned aircraft, will also to be built in with sensor costs and complexity driving up costs.

The last is a very important aspect – that of the threat posed by UAVs. An unarmed remotely controlled UAV is a precision guided munition in itself. The Harop UAV in service with the IAF is designed to collide with a target – a capability that any commercial UAV already has. Anti-UAV weapons including helicopter launched nets to snare UAVs are being developed and even training falcons to hunt small UAVs is being explored. The weaponised helicopter is probably a good platform for taking down slower UAVs. There have already been instances of UAVs being deliberately flown towards airliners on approach for landing. The UAV will sooner than later become a potent tool of asymmetric warfare in the hands of terrorists and measures in addition to regulations have to be incorporated to guard against this threat.