From 3 March 2020, ADS-B data collected by satellite was made available to all users. Aircraft located using satellite data are coloured blue on the map, and yellow if located by terrestrial receivers.
A note about Estimated coverage: when you see a dashed or gray line behind an aircraft, that's estimated coverage. Colored lines indicate actual positions. When an aircraft is out of coverage, we estimate based on great circle routes to destination.
A purple line on an aeronautical chart typically indicates an airway, which is a defined route through the airspace that connects two navigation aids, such as VOR (Very High Frequency Omnidirectional Range) stations. Air traffic controllers use airways to route aircraft along designated paths in the sky.
The most well know of these is the code 7700. This is used to indicate an emergency of any kind. A pilot will enter this when in an emergency situation - either instructed by ATC after declaring an emergency or without communication if there is no time.
It appears as BLOCKED due to security and privacy reasons. Aircraft type - (It will only show the 'type code' [LJ35,C750,PA31,etc)] of the aircraft on flightradar24 map. Blocked - Any aircraft without any type codes in the database.
The second emergency squawk code is 7600, showing ATC that the aircraft has lost verbal communication. This could mean that it can still hear ATC and yet not respond, in which case the ATC will direct the pilot to speak with them through the Ident button.
It means the owner has requested that the craft's details (tail #, filed flight plan, etc) not be displayed. Law enforcement helicopters are also blocked if they are doing something “undercover” where they don't want someone to know they are in a given location.
If the 7500 squawk code is mistakenly selected, the pilot will immediately receive a call from air traffic control asking for confirmation. At this point, the pilot in command or the first officer is able to inform the transponder code has been used by mistake, and that there is no hijacked aircraft.
Flightradar24 is the first flight tracking service which offers space-based ADS-B-tracking. The blue planes on the map are tracked from a satellite and the yellow ones are tracked from the regular earth-based radar stations.
These clouds are contrails, short for condensation trails. Water vapor is one of the byproducts of jet fuel combustion and will turn into ice crystals in the cold air at the high elevations where jet airplanes fly. Those ice crystals create a cloud (the contrail), which does not pose any public health risk.
According to USA Today, the common cruising altitude for most commercial airplanes is between 33,000 and 42,000 feet, or between about six and nearly eight miles above sea level. Typically, aircraft fly around 35,000 or 36,000 feet in the air. To put that in perspective, the peak of Mount Everest measures 29,029 feet.
While it may sound shocking to some, the simple fact is that some aircraft may simply not have their transponder on, or it may be temporarily off, or they may be carrying passengers or cargo, which warrant deactivation. In addition, not all airspace activity is always relayed to FlightRadar24 at all times.