By Oleksandr N.
[Note: Oleksandr originally posted a link to this intriguing paper in the comments section, where it has generated a considerable amount of discussion. Oleksandr has developed one of the most intriguing hypotheses about the Inmarsat data to emerge in a long time. In a nutshell, he suggests that data that has long been viewed as spurious might in fact be an important clue as to what the plane was doing during two crucial and as-yet poorly understood periods of its final flight. — JW]
There are two obviously abnormal BFO values of 273 Hz (18:25:34.461 UTC) and -2 Hz (00:19:37.443 UTC) recorded by Inmarsat. The first of them is inconsistent with the other BFO records in the same cluster of BFOs 18:25 – 18:27, and it is also inconsistent with the known heading and speed of the aircraft by 18:22.
The second abnormal BFO value of -2 Hz considerably differs from the BFO value of 182 Hz just 8 seconds earlier. Should this value be correct, it would imply an extreme descent rate (~15,000 ft /min).
While attempts took place to explain the BFO of 273 Hz as a result of some maneuver, such as a lateral offset, the second anomalous value of -2 Hz is widely believed to be erroneous.
This technical note provides an alternative view, suggesting that both the anomalous BTO values are valid, but they are the results of the inability of AES to apply Doppler compensation due to missing position/velocity data.
You can find the whole paper here.