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Unmanned Aircraft Systems

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Category: General General
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UAS - Unmanned Aircraft System, UAV - Unmanned Air Vehicle, RPV - Remotely Piloted Vehicle, RPS - Remotely Piloted System

Contents

Definition

A system comprising an unmanned aircraft, remotely controlled, usually from the ground but also from manned aircraft, data links, and sensors.

Description

The development of Unmanned Aerial (Vehicle) Systems - UAS - began as a means to undertake aerial tactical surveillance using small flying machines equipped with cameras. The term UAS has emerged as successor to the earlier term UAV (Unmanned Aerial Vehicles) in recognition of the fact that a UAV itself is merely a part of the system which is required to operate the unmanned aircraft.

The process of gathering of intelligence information for military or quasi-military purposes has become collectively known as ‘Intelligence, Surveillance, Target Acquisition and Reconnaissance - ‘ISTAR’ and has subsequently been hugely enhanced by the use of UAS with a much greater range of sensors. These aircraft are now routinely employed by border patrol agencies as well as by some army, air force and naval military commands. More recently, larger UAS have been developed to carry weapons. UAS is a rapidly growing sector of aviation with increasing civil applications, such as pipeline survey, and growing demand for these aircraft to be able to operate in unsegregated airspace.

The Role for and Delivery of UAS Operations

UAS have become increasingly capable and, compared with manned aircraft, well suited to missions which involve some or all of what have been described by the UK Ministry of Defence as the “4 Ds”. These are missions which are:

  1. Dull - they require persistence or repetition.
  2. Dangerous - they carry a high degree of risk.
  3. Dirty - they must be carried out in hazardous environments.
  4. Deep - they are beyond the range of tactical aircraft manned platforms.

The range of UAS aircraft sizes varies considerably. The smallest are hand-launched and have a maximum flight endurance of about an hour. They are small enough to be barely visible in action and often go unnoticed by people on the ground. Smaller UAS are mostly used for tactical support of ground troops engaged in potentially hostile environments and are controlled by soldiers in the immediate theatre of operations. Because of this, and subject to training missions being undertaken in restricted airspace, they are unlikely to be encountered by conventional air traffic. The largest UAS in regular service currently are equivalent in size to a medium-sized light aircraft. The most widespread current example of these is the Reaper which has an MTOM of around 4500kg and a wingspan of 20 metres and is powered by a single engine driving a pusher propeller. Larger UAS in service include The Global Hawk has the same wingspan as a Boeing 737.

Predator B
Reaper- notice that this UAV carries a selection of air-to-ground weapons

UAS Control

UAS control generally requires line of sight to maintain full control by radio signalling on the frequencies used. Some UAS also have a satellite-based back up control with limited authority available in case of any transient loss of the main control capability. The ground based operator of a manned-aircraft-sized UAS is usually called a pilot but is not necessarily a current or previously qualified manned-aircraft pilot. The surveillance or weapons delivery equipment in such UAS is usually the responsibility of a second co-located technician. Time for individual pilots at the control station can be lengthy and, unless the mission being flown is in an actively hostile environment, and involves tactically responsive oversight, can be very boring, a situation where human performance errors with significant consequences could easily occur. Hand over procedures from one pilot to another, and the communication between the pilot and the payload pilot (no. 2) are also recognised as problematic.

As an example, the following describes the control arrangements for the Global Hawk (GH)/Euro Hawk (EH):

"Launch and Recovery Elements (LREs) located at the Main Operating Airfield or a Forward Operating Location will control GH during taxi, launch and recovery. However, for most of the mission, GH will be controlled by a Mission Control Element (MCE, The USN term for a MCE is a Tactical Auxiliary Ground Station (TAGS)), which may be located at the Main Operating Airfield or elsewhere. The MCE is able to provide command, control and communications redundancy in the event of a failure of any of these at the LRE. Each MCE will be supported by a GH Operations Centre (GHOC, supporting flight ops at all times). Amongst other things, the GHOC provides supervisory oversight and expertise, and filters and prioritises information flows to the MCE. Normal GHOC manning comprises a pilot and a sensor operator to support their counterparts in the MCE, plus a duty officer. Typically, one member of the GHOC will be a qualified GH instructor who is therefore well-placed to provide support to the MCE in the event of an emergency. The GHOC also oversees handovers between MCE crews in a structured way that ensures safe and positive control of GH at all times." - ATM Guidelines for Global Hawk in European Airspace.

ATM Issues

Although the pilot of a UAS operated outside a militarily hostile environment must maintain R/T contact with the relevant controlling ATC authority and obtain appropriate clearances to operate, the present Regulatory Requirements for UAS are exactly the same “Rules of the Air” as manned aircraft. This includes a requirement to ‘see and avoid’ other air users which cannot currently be satisfied by any unmanned aircraft, so that UAS flights can only take place in a fully controlled ‘closed’ ATS environment where any civil air traffic will be accepted only subject to specific permissions and restrictions. The development of a modified regulatory framework for ‘sense and avoid’ will, in time, allow UAS operation in non-segregated airspace.

UAS operation might also take place outside segregated airspace, e.g flying on FL above the normal ones, e.g FL 550. Additionally Germany undertook a safety case for Euro Hawk flying inside normal airspace above FL 100 and considered it to be safe. GH and EH operations on a low scale in Germany and Italy are expected to be performed as follows:

"The GH operations described are flown by the military, and are therefore classed as Operational Air Traffic (OAT) . These Guidelines accordingly follow the same basic ATM principles as the EUROCONTROL Specifications for the Use of Military UAS as OAT, namely that:

  • UA operations should not increase the risk to other airspace users.
  • ATM procedures should mirror as much as possible those applicable to manned aircraft.
  • The provision of air traffic services to UAS should be transparent to ATC controllers" - ATM Guidelines for Global Hawk in European Airspace.

In recent years considerable interest and effort has been expended world-wide into the development of technologies, ATM procedures, UAS operational approvals and UAS certification standards that will allow UAS to become fully integrated into the Air Traffic Management (ATM) environment. In 2010 EUROCONTROL have commissioned a study to demonstrate that there is a need for UAS to have a collision avoidance capability comparable to that delivered by ACAS on manned aircraft (see Further Reading).

The European Aviation Safety Agency (EASA) has published a "policy" establishing general principles for type certification (including environmental protection) of UAS (see Further Reading).

Operational Safety

Study of accidents and incidents to the larger UAS so far has shown that, whilst mechanical and control failures are sometimes the main cause, human factors are a major issue and it will be important to identify such causes during investigations. It has also been found that most investigations of such events have disclosed major latent errors in the system devised to facilitate UAS flights.

Further Reading

EUROCONTROL

EASA

FAA

Others

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