Aircraft spotting is a hobby involving the pursuit of different aircraft: gliders, powered aircraft, large balloons, airships, helicopters, microlights and, less probably, drones and hovercraft.

Virgin Atlantic Airbus A340. The picture was taken from Myrtle Avenue, an excellent aircraft spotting location at the south east corner of London (Heathrow) Airport (UK).

When spotting planes, observers notice the key attributes of an aircraft. They may notice a distinctive noise from its engine(s) or the number of vapour trails it is leaving against a blue sky. After that, they will assess the size of the plane and the quantity, type and position of its engines. Another clue is the position of wings relative to the fuselage and the degree to which they are swept rearwards. Are those wings above the fuselage, below it, or fixed at midpoint? Perhaps it is a biplane or triplane. The position of the tailplane relative to the fin(s) and the shape of the fin are also conspicuous clues to its type. If it is an antique or light aircraft it might have a tail wheel. Some aircraft types have a fixed undercarriage whilst others have retractable wheels. Other features may come into view, the speed, cockpit placement, colour scheme or special equipment that changes the silhouette of the plane. Taken together these clues will rapidly hasten the correct identification of a plane. Obviously some types are easily confused whilst others have more distinctive attributes. If the observer is familiar with the airfield being used by the aircraft and its normal traffic patterns, he or she is more likely to leap quickly to a decision about the aircraft's identity - they may have seen the same one many times from the same angle!

The challenge lies in the identification of aircraft -- their manufacturer, type, mark and perhaps serial number -- often in difficult circumstances (e.g. when at some distance or when obstructed by others or in darkness). Some spotters will deduce further information from its markings, a national insignia or airline livery or logo perhaps, a squadron badge or code letters in the case of a military craft. Published manuals allow more information to be deduced, such as the delivery date or the manufacturer's construction number. Camouflage markings differ widely across the globe, depending on the surroundings in which that aircraft is expected to operate.

Ancillary activities might include listening-in to air traffic transmissions (where that is legal), liaising with other "spotters" to clear up uncertainties as to what aircraft have been seen at specific times or in particular places, and the drawing, painting, filming, tape-recording or photographing of aircraft.

The more enthusiastic hobbyists might travel great distances in order to see particularly unusual aircraft, or even the remains of aircraft withdrawn from use. Some such "wrecks and relics" may eventually be placed in the care of museums - or perhaps be cannibalised in order to repair a similar aircraft already preserved. Some spotters may go on to work in the aviation industry or air traffic control service.

During WWII and the subsequent Cold War some countries encouraged their citizens to become "plane spotters" in an "observation corps" or similar public body for reasons of public security. Latterly, an Open Skies initiative has extended the principle of short-notice cross-border inspections as a basis for international confidence-building, reducing significantly the chances of international misunderstandings. NATO members and other signatories to the Open Skies Treaty initiative have agreed to exchange information about military exercises in advance.

Some spotters are quite competitive and may get a thrill from seeing, in due course, all the planes of a particular type ever built (or extant at that date). Spotters are generally well-aware of the hazards facing aviators and will stay alert when near active aerodromes, taking care not to interfere with aircraft or cause anxiety to their owners or users.

Many airfields in Australasia, Europe and North America recognise the public's interest in aviation as something to be encouraged and provide viewing areas in safe locations. Many organised airshows draw large crowds and some raise funds for charitable causes such as museums, organisations restoring historic planes, or bodies that assist injured aircrew or the dependents of Armed Forces' personnel. Some shows have a more commercial motive, and some aircraft photographers can make a profit from their onetime hobby. The World Wide Web has provided a new outlet for some of their photographs and assists all spotters in letting each other know what is flying where.

Aircraft spotting was not until recently recognised as a legitimate hobby in Greece where the military authorities remain concerned about note-taking and photography on or near airfields. This attitude resulted in an international dispute in 2001/02 between the Netherlands, United Kingdom and Greece following the arrest on spying charges of 2 Dutch and 12 British plane spotters travelling together, who had been invited to the Hellenic Air Force Open Day at Kalamata. After they had spent over a month in prison, three judges sitting as a Panel in Kalamata reduced the charge on 12th December to "accessing national secrets" and on payment of bail the 14 spotters were allowed to travel home. A trial was eventually held in a local Greek court and on 26th April 2002 they were found guilty of espionage. For some of the group a three year jail sentence seemed likely, all were allowed to travel home on payment of bail money pending an Appeal.

All except one of the group (who did not return to an Appeal court in Kalamata for medical reasons) were acquitted of all the charges on 6th November 2002. Some media continue to suggest that they had taken photographs on or of military facilities or operational aircraft, this was not the case. At least one is still fighting to revcover his bail money.

One side-effect of the case was the heightened awareness it brought in the UK to the human rights implications of mutual extradition agreements anticipated between the member states of the European Union. Would European citizens find such arrangements bearable when one country chose to adopt a critical approach to an activity whose legality is unlikely to be questioned across the remainder of the Union?

See bus spotting, train spotting, birding and butterfly spotting for examples of similar hobbies.