Airspace classes explained
Airspace is divided into classes and zones, each with its own rules about who may fly and under what conditions. Understanding this structure helps you interpret what you see overhead — and whether it should be there at all.
ICAO airspace classification is used worldwide. Each class has its own rules for access, communication, and separation. As a ground observer, the class gives you an idea of what traffic to expect.
Class A — Upper airways
IFR only (instrument flight rules). Upper layers from FL245 (~7,500 m). No VFR traffic. Exclusively military and commercial aviation at cruise altitude. What do you see? High-altitude airliners — sometimes visible as thin contrail lines during the day.
Class C — Major airport TMA
Controlled airspace around a major international airport's Terminal Manoeuvring Area. IFR and VFR permitted with ATC clearance. Intensive commercial traffic — arrivals and departures following strictly controlled approach paths (SIDs and STARs).
Class D — Regional aerodromes
Control Zone (CTR) around smaller airfields. VFR permitted with radio contact and clearance. General aviation, business flights, flying clubs. Lower traffic density than Class C.
Class G — Uncontrolled airspace
Most low-altitude and rural areas. VFR without mandatory clearance, though VHF radio is recommended. Ultralights, model aircraft, balloons, paragliders, gliders, and recreational drones all operate here. The most 'open' airspace class.
Airspace in many countries contains a network of temporarily reserved and segregated zones for military activity. These zones are activated dynamically via the NOTAM system.
TRA — Temporary Reserved Airspace
Temporarily reserved for military exercises but not fully closed to civil traffic. Activated via NOTAM for specific time windows. When inactive: ordinary airspace. Sky Lens shows the current NOTAM activation status in real time — so you know whether a TRA was active at the time of your sighting.
TSA — Temporary Segregated Airspace
Fully closed to civil aviation during military activity. No civil aircraft may enter these zones while they are active. TSA areas are typically located around military air bases and are among the most actively used zones in the national airspace system.
NOTAM system
NOTAM stands for Notice to Airmen — official messages announcing temporary changes to airspace. Military exercises, airshows, drone operations, and other temporary restrictions are all communicated via NOTAMs. Sky Lens loads current NOTAM data daily.
Permanent prohibited zones (P-zones)
Permanent prohibited zones exist over critical infrastructure: government buildings, nuclear installations, and certain security-sensitive sites. These apply 24/7, regardless of NOTAM activation, and are visible on the Sky Lens map.
Drone regulation under the EASA framework (European Union) is broadly representative of modern aviation authority frameworks worldwide. Categories determine where, how high, and with which drone you may fly.
Open Category A1 — Mini drones
Drones under 250 grams. May fly over people (but not over crowds). Maximum altitude 120 m. No registration required for drones under 250 g without a camera. Lowest risk, most freedom.
Open Category A2 — Consumer drones
250 grams to 4 kg. Mandatory horizontal safety distance from people. Maximum altitude 120 m (or 50 m in certain cases). Registration with the national authority required. Theoretical exam required (A2 certificate). Remote ID required.
Open Category A3 — Professional drones
4 to 25 kg. Must fly well clear of people — minimum 150 m from residential areas. Maximum altitude 120 m. Registration and certification required. Remote ID required. Typical uses: agriculture, inspection, and film production.
Specific Category — Special operations
Everything outside the Open Category: drones over 25 kg, night flights, beyond-visual-line-of-sight (BVLOS) operations, flights over crowds. Requires an Operational Authorisation (OA) from the national authority, including a SORA risk assessment. Can take weeks to months.
Exclusion zones
Drones may not fly: within 5 km of aerodromes (without explicit permission), over crowds, over prisons, over nuclear installations, over government buildings, or inside P-zones. Sky Lens shows all exclusion zones on the map.
Knowing which airspace class applies to your location lets you estimate what traffic to expect — and what traffic definitely should not be there.
Location sets the context
Near a major international airport (Class C) you can expect intensive commercial traffic on fixed approach paths. In a rural area with Class G airspace, ultralights, paragliders, and recreational drones are the norm. Sky Lens shows your airspace class on the map.
NOTAM status contextualises military traffic
If a TRA is active over your region and you hear a jet aircraft pass at low altitude — that is legitimate military exercise traffic. Sky Lens shows which TRA/TSA zones were active at the time of your sighting so you can verify this yourself.
Absence of ADS-B is informative
If Sky Lens finds no ADS-B aircraft matching your sighting, but you are close to a military base — a non-transponding military flight is a realistic candidate. The absence of data is itself a data point.
Drone exclusion zones
If you see an object behaving like a drone but you are inside an exclusion zone — the probability of an unauthorised drone increases. Sky Lens shows all exclusion zones and flags whether your location is inside one.
Sky Lens combines ADS-B data, NOTAM activation status, airspace classes, and drone exclusion zones to interpret your sighting — including whether the object was authorised to be there.