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Flights broadcasting false ADS-B altitude information

We have been monitoring air traffic over the UK, in particularly over London, for the past 4 years. It dawned on us quite quickly that something was amiss in terms of the altitude information that certain flights were broadcasting. If an aircraft is at 37,000ft – which equates to 7 miles high to put it in more layman’s terms – you cannot really see it with the naked eye. If you can see it at all it will be the trail of chemicals it is leaving in its path that you can see rather than the aircraft itself.

While filming in London we started to notice that transient flights travelling through UK airspace were flying a lot lower than the flight tracking websites were telling us. It’s is an easy thing to notice. As a rule of thumb, if you can make out the features on an aircraft, such as the tail-fin logo, the engines, the wings etc, then that aircraft is likely travelling below 20,000ft.

We have since filmed many flights over London that are clearly travelling at well below 20,000ft but are shown on as travelling at much higher altitudes more consistent with transient, long-haul aviation such as 34,000-40,000ft.

There are 2 primary reasons for doing this.

  1. Official MET Office figures for the formation for natural contrails state theta the conditions necessary are -57 Celsius, which is normally only found at altitudes of around 37,000ft depending on the time of year. The rough equation for working this out is that atmospheric temperature tends to drop by 1 degree Celsius per 1000ft increase in altitude. This is confirmed by MET Office radiosonde data. This obviously means that if an aircraft is releasing substances during flight it needs to avoid suspicion by giving the impression that it is at an altitude whereby natural contrails can form. Leaving aside the fact that natural contrails do not persist for more than a few seconds, this is a blatant attempt to mislead people.
  2. Normal cruising altitude for long-haul flights is over 34,000ft. This is very simply to reduce operating costs. Air pressure is much lower and hence drag is greatly reduced, resulting in increased fuel efficiency.

It is much more expensive to fly low than it is to fly high, so why then do we see regular flights over UK airspace of transient aviation flying as low as 12,000 – 16,000ft?

Here is a short film we made in West London showing a great example of this phenomenon:

False ADS-B altitude data