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   A knowledge resource for the UAS sector

Content in this website is still growing - more will follow

Under the group headings in the menu are pages dealing with particular topics and subjects, which include descriptions, concepts, hyper-links to useful Web-based knowledge and downloadable .pdf files, which may include studies and discussion papers.

This site is run by volunteers on a non-profit basis.  It does not claim to be authoritative.  The content offered is intended to facilitate the growth of knowledge about UAS and is provided in good faith and without prejudice. Please refer to the ‘This Site’ page in the About section.

This independent website is associated with the Unmanned Aircraft Systems Specialist Group of the Royal Aeronautical Society (   This Specialist Group is looking to be renamed Remotely Piloted and Autonomous Aircraft Systems Specialist Group (RPAAS SG).  For more information, please refer to the ‘This Site’ page in the About section.

UAS, RPV, UAV, drone, RPAS or RPAAS?

There have been many names which all refer to an aircraft with no human pilot on board.  Back in the 1970s, an early term was Remotely Piloted Vehicle (RPV) but this was also used for land and maritime vehicles so the term Unmanned Aerial Vehicle (UAV) followed and was used for many years.  Many working in the sector thought that ‘aerial vehicle’ set these aircraft aside from mainstream aviation and since the aim was for them to fly alongside ‘regular’ aircraft in non-segregated airspace a new name was needed.  This became Unamnned Aircraft System which not only had the key word ‘aircraft’ in the name but also embraced the fact that the UA was part of a bigger system, necessary for safe navigation.  UAS is still very widely used.

UAS can be said to have two sub-categories, the first which has a human pilot, albeit remote from the aircraft, who is responsible for safe navigation at all times; the second is where the UA can and does fly full flight missions without any human intervention.  Most regulators around the world are addressing rules, regulations, law, guidance, standards and recommended practices for the first sub-category, now called Remotely Piloted Aircraft Systems (RPAS) but are not yet focusing on the second sub-category.  Many refer to this category as Autonomous Aircraft Systems (AAS) but equally many are uncomfortable with ‘full autonomy’ (there are host of different views on autonomy…) and would prefer Automatic Aircraft Systems (also AAS).

For this and other reasons, some in the sector are looking to adopt the term Remotely Piloted and Autonomous (or Automatic) Aircraft Systems (RPAAS) to cover all aircraft with no human pilot on board.

Unmanned Aircraft Systems (UAS) - Introduction

The UAS sector has many abbreviations and special terms.  The Terminology page with downloadable .pdf file may be helpful.

An unmanned aircraft (UA) may be described as an aircraft with no human pilot on board.  Two broad classes of UA can be identified, one in which the UA completes a flight mission from start to finish completely automatically without any human supervision nor intervention and one in which the UA has, at all phases of a flight mission, a human pilot who is capable of exercising his or her responsibility for safe navigation of the airspace at all times, therefore with the ability to supervise all phases of the filght and to intervene when necessary.  Currently the completely 'fully automatic class' is not subject to concerted regulatory action since it does not meet the requirements of most national and international authorities.

The second type of UA, for which a pilot is responsible at all stages of a flight mission and can intervene as required to ensure safe navigation, is now (2020) subject to a huge range of regulatory action and standards work with the aim of routine operations in non-segregated airspace.  This type of UA is commonly termed a Remotely Piloted Aircraft (RPA) to emphasise that there is a human pilot responsible for and capable of assuring safe navigation.

Since there is no human pilot on board these aircraft, they require a system to enable safe navigation.  In the case of the RPA, there is typically the need for one or more types of communications to and from the pilot and for a Remote Pilot Station from which the pilot operates.  Depending on the aircraft and communications, there may also be a need for launch and recovery crews, antenna arrays, radio rebroadcast relays, satellite and/or non-radio frequency communications and other systems components.  Therefore both UA and RPA are best addressed with a full systems approach.  Since many parts of a UAS or RPAS may be safety critical, safety certification also needs to use a system approach - see the Airworthiness page.  Unless there is a particular need to differentiate, the terms RPA and RPAS will be used.

Differences from Manned Aviation

The main difference is that there is no human pilot on board the aircraft.  This means that a full systems approach has to be used to a different degree from manned aviation (eg the communications are even more important).  The Remote Pilot (RP) is unable to have a direct ‘aircraft perspective’ both in terms external and internal situational awareness so the system has to mitigate this.  There are also a range of issues about Human Machine Interface (HMI) and other Human Factors (HF) issues including behavioural and ethical considerations.  A key issue is that, depending on the payload requirements, there is no need to cater for a human pilot.  Therefore RPA can be very small and economically efficient, which opens up a vast new range of aviation applications which would not have been affordable using manned aircraft.

At the moment (2022), the carriage of human passengers on RPA is not approved.  There is serious consideration of using RPA for ’search and rescue’ type missions, in which a human who is already in peril could be airlifted to safety by a RPA in exceptional circumstances.  However routine passenger operations by RPA are not yet happening.

Not having human life on board an RPA makes a big difference to the safety and risk considerations.  Manned aviation safety has evolved over the last hundred years or so with the main focus on preserving human life on board the aircraft.  This meant that any risk of incident, either with other air users or with terrain or bad weather had to be mitigated to the required extent - to an acceptable level of risk.  This means not only that the airworthiness of the aircraft has to be to a very high standard but also that the risk to other airspace users and people on the earth’s surface is very low.  The majority of manned aircraft, once they have received safety certification, are authorised to fly in most environments, such as over centres of population.

Since there is no risk to human life on board an unmanned RPA, the risk assessment focuses on the risk to other airspace users and those on the surface.  The risk in remote areas with negligible air traffic and terrestial population density is therefore hugely lower than in the proximity of a major commercial aviation hub in a densely populated area.  The operational risk for an unmanned RPA is a function of the RPAS and, crucially, the operational environment (which includes many factors).  This enables optimising RPAS for specific operational scenarios delivering not only the required level of safety but also economic efficiency.  The greater  the operational risk, the greater the safety mitigation required from the RPAS.


The term ‘drones’ is in common use for UA/RPA and is not problematic in itself, so long as there is a full understanding of what a ‘drone’ might be.  UA/RPA are not just small consumer aircraft which are available from retail stores.  They range from tiny experimental aircraft weighing tens of grams up to large aircraft weighing several tons.  It also has to be clear whether ‘drone’ refers just to the UA/RPA or the whole system, UAS/RPAS.

RPAS and Model Aircraft

Model aircraft have been flown remarkably safely by enthusiasts for many decades.  They are flown for purely recreational purposes and the people who fly them typically enjoy controlling the the aircraft directly using a remote control console and communications channels which are pubicly available.  Most model aircraft fliers traditionally have shunned autopilots.  However, with the mass expansion of the consumer ‘drone’ market, this has changed.

RPA are flown to do ‘aerial work’ for (typically) financial gain or as part of commerical operations.  In most cases the operators are less interested in the pleasure of flying but more on the output delivered by the RPAS.  Thus the use of autopilots and other automation is the norm.

Several states and regions are now moving towards a unified approach to regulation of all RPAS, whether they are operated for gain (aerial work) or for recreation.  For more on this topic from a UK perspective, see the UK page in the Regulation section.

The text above has only provided a short introduction to the content in this site.  The main sections listed in the menu bar deal with topics in more detail and provide links and other content for further reading and research

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