Originally Posted by
Airbubba
Ian at FlightRadar24 has harvested some indicated airspeed data from the extended Mode-S data fields:
Additional Extended Mode S data decoded
Flightradar24 has now retrieved and processed extended Mode S data from individual receivers in the area. Unlike ADS-B data, which always contains the same known data points, Extended Mode S may contain data from a variety of fields like aircraft identification, meteorological data, heading, speed, and others. The data sent varies based on the fields requested by the Secondary Surveillance Radar ground stations used by air traffic control.
The data sent via Extended Mode S does not include the Binary Data Selector (BDS) identifying the type of data. Flightradar24 interprets this data using advanced scripts and historical comparative data, but there may be errors in individual frames due to misinterpreted data fields. Overall trends in the data are correct as reported. We have included the raw data, downloadable below.
Included in much of the Extended Mode S data sent by PK8303 were data on Indicated airspeed. The below graph shows the aircraft’s calibrated altitude and Indicated airspeed from 10,000 feet to the final data received.
More detailed study of the FR24 "Extended Mode S data" (i.e. the
EHS parameters) confirms that extreme caution needs to be exercised when reaching any conclusions based on the decoded values.
While the IAS values in the FR24 data may or may not be accurate, the accompanying TAS values clearly aren't. I queried this by email with FR24 and received only a boilerplate response, so I've just asked the same question on their Twitter feed:
"Can you explain why the True Airspeed (TAS) values in your download, before and during the go-around, are consistently shown as 314 knots? That's up to 140 kts higher than the IAS values at the same point in time, which is clearly nonsense."
Similar considerations apply to the Heading values in the FR24 dataset, which show near-instantaneous heading changes of 180° or more at a couple of points.
I'll post any response that I receive.