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.
152 thoughts on “Guest Post: On the possible interpretation of abnormal BFO values”
In the 71s from 18:27:04 to 18:28:15, BTOs decreased by 40-80 microseconds from 12520-12560 to 12480. That translates into an average velocity TOWARDS the satellite of 330-660kts. That requires that the a/c velocity was directed largely TOWARDS the satellite during that period.
Now, during that interval, the sub-satellite ground location was WSW (~265*) of the a/c near NILAM. And, the relative elevation to the satellite was over 50 degrees above the horizon. Approximately, Cos[50*]=3/4, so even if the a/c was travelling at
500kts directly towards the SUB-satellite point on earth, the velocity component
towards the SATELLITE out in space would still only have been about 500*(3/4) = 370kts… already near the minimum of the range allowed by the BTO data.
Mathematically conversely, THE minimum airspeed consistent with the BTO data would be (4/3)*330kts = 440kts, and then only on a heading directly towards the sub-satellite point (~265*).
Thus, prima facie, the BTOs from near NILAM suggest a FMT, towards the SW, at high air speed (>440kts). More stringently, a turn to the NORTH, would have carried the a/c AWAY from the satellite during that period, and so seems inconsistent with the BTO data.
Moreover, since the FMT seems to have been sharper, onto a SSW heading (<=195*), only higher airspeeds (~500kts) have enough "velocity to spare" to "stray away" from the satellite location by so many degrees.
BTO data seems to require an FMT, near NILAM, around 2:25-2:28am, at high speed (440-500kts).
From near NILAM to sub-satellite point, at about 2:25am, is a WSW heading of approximately 260*
And, the elevation angle from there to the satellite was about 52*.
And, the COMPONENT of a/c velocity TOWARDS the space vehicle would have been roughly:
330-660kts = v_parallel = v_total * Cos[elevation] * Cos[heading-260*]
Cos[elevation] = Cos[52*] = 3/4
v_total <= 500 kts
330*(1-2) = 500 * 3/4 * Cos[heading difference]
440/500 * (1-2) = Cos[heading difference]
ArcCos[0.88++] = heading difference 440kts requirement of the BTO data…
Nor is completing the FMT prior to 2:27am and already being on a SSW heading of 195* from then onwards, which is far outside of the 30* deviation from 260* allowed by the BTO data (even at 500kts)…
And, further, according to Wiki, BTJ airport probably hosted well over 20,000 a/c and 2,000,000 persons in 2014. That’s about 70 planes and 7000 people per day, on average. It was of course closed from 1800-0700, but maybe too busy of an area for no one to notice if the a/c was there ??
CONCLUSION: Dr. Ulich’s “Maimun Saleh” scenario seems more mathematically likely than a “Banda Aceh” scenario; and, FMT completed after 2:28am
PS: best fit elevation for 2:40am sat-phone call is 53*, if so, then a/c continued to move more-than-less WSW from 2:28-2:40, i.e. not more than 90* from 260*