This is an update to the original posting.
August bank holiday Monday, 2016, was a sunny day and for most of that day, airplane trails were noticeably absent from Liverpool’s skyline. That was until late evening when I was drawing the curtains and noticed a sudden rash of white trails hanging over the city. I therefore went onto Planefinder to see if I could identify the aircraft responsible for this atmospheric graffiti. While I cannot be sure that the plane detailed below was the source of the trails, there is no doubt that its flight path is highly suspicious.
What I later discovered about this is odd journey is that it did not happen. It turns out that this strange flight path is a processing error by the Planefinder website. This particular ‘Flybe’ plane is not transmitting its flight details by using a system called Automatic Dependence Surveillance Broadcast (ADS-B). Currently, ADS-B is not mandatory but it is the new standard that is being introduced over time and all planes will eventually be compelled to use it. Consequently, this flight has been tracked through the use of ground stations and a system called Multilateration (MLAT). The problem with MLAT is that it requires a minimum of 3 groundstations to detect a plane in flight and to accurately calculate its position. The Planefinder website then uses the data about a plane's position to track its flight path and display it on screen.
The screenshot above describes 6 of the 8 flights that this plane undertook on 29 August 2016. Somehow, the Planefinder software has failed to realise when the plane has landed, so that it can terminate the flight. Instead, when the plane has taken off again, the software has assumed that it is continuing on the same journey. It has also filled in the flight data gaps created when the plane landed, so that it appears to be the continuation of a long and circular flight.
This has taught me an important lesson about MLAT data. I believe that aircraft are involved in spraying activities over large parts of Britain. However, it is important that the evidence collected is as robust as possible, otherwise it undermines attempts to get others to take the issue seriously.
There is another website called FlightRadar24, which provides similar flight details to Planefinder and it is worthwhile cross-checking flight details across both websites when observing what appear to be suspicious flight activities.
Most of the strange flights that I have observed are by non-commercial aircraft whose journeys are tracked by MLAT. However, it is possible that these flights have also been inaccurately described because of the same problems to the ones described above.
While ADS-B is a reliable system, MLAT does have shortcomings and these need to be recognised when observing what appear to be unusual flight patterns.