Aerospace and Electronic Systems Magazine February 2018 - 32

MH370 Burst Frequency Offset Analysis
Table 4.

MH370 Descent Rates at 00:19Z, 8 March 2014, Under Hypothesis 1
Time Stamp

Min. Desc. Rate,
South Track (fpm)

Min. Desc. Rate,
North Track (fpm)

Max. Desc. Rate,
South Track (fpm)

Max. Desc. Rate,
North Track (fpm)

00:19:29Z

3,900

5,100

13,600

14,800

00:19:37Z

14,800

15,900

24,100

25,300

Min., minimum; Max., maximum; Desc., descent.

Table 5.

the plane was descending at a rate between 2,900 and 6,800 fpm.
At the time of the last SATCOM message, it can be concluded
under Hypothesis 2 that the descent rate would have been between
13,800 and 17,600 fpm.

The Last Two BFOs for MH370 Under Hypothesis 2
Time Stamp

Recorded BFO
(Hz)

BFO Bounds
with Noise (Hz)

00:19:29Z

182

[164, 210]

00:19:37Z

−2

[−20, 26]

SUMMARY OF DESCENT RATE BOUNDS
Combining the descent rate bounds for Hypotheses 1 and 2, outer bounds can be established for the descent rates of MH370 at
00:19:29Z and 00:19:37Z. Specifically, regardless of ground track
angle and for ground speeds less than approximately 500 knots,
accounting for possible BFO noise and regardless of whether the
SATCOM outage between 00:11Z and 00:19Z was due to an SDU
power outage or another reason, the outer bounds on the possible
descent rates at the times of the last two SATCOM messages from
MH370 are given in Table 7.

by 1.7 Hz and multiplying by 100 fpm. The expected BFO for
a south track is approximately 260 Hz, while for a north track
it is close to 280 Hz. Using these numbers, it is straightforward
to obtain the bounds shown in Table 4. The bounds have been
rounded to the nearest 100 fpm. Looking at all values in the table,
it can be concluded that irrespective of ground track angle and for
assumed ground speeds less than approximately 500 knots, under Hypothesis 1, MH370 would have been descending between
3,900 and 14,800 fpm at 00:19:29Z and 8 s later would have been
descending between 14,800 and 25,300 fpm. These descent rates
are consistent with simulations of an uncontrolled phugoid descent reported in [6].

ESTIMATED DOWNWARD ACCELERATION
When interpreting the bounds presented in Table 7, the conditions under which each bound was derived need to be considered.
For instance, the lowest rate at 00:19:29Z was derived assuming no period of SDU outage and a southward track, whereas the
highest descent rate for 00:19:37Z was derived assuming a 1-min
outage of the SDU with the maximum BFO decay observed in
the previous seven SDU outage events for 9M-MRO. Hence, it
would not be reasonable to say that the plane could have been
descending at 2,900 fpm at 00:19:29Z and 25,300 fpm 8 s later,
which would imply a downward acceleration on the order of
2,800 fpm per second. While it is not possible to determine a
precise acceleration value, a rough approximation of the average
descent rate over those 8 s could, for instance, be taken using the
midpoints of the bounds at each time, which would result in an
average downward acceleration of 10,700 fpm in 8 s, or around

HYPOTHESIS 2: SATCOM OUTAGE DUE TO SOME OTHER REASON
It is still of interest to determine bounds on the descent rates under
the alternate hypothesis that something not associated with a power outage led to the SDU-initiated log-on event at 00:19Z. In this
case, the warm-up drift would not apply. Therefore, the recorded
BFOs can be treated normally (though still subject to BFO noise).
In this case, the BFO bounds are as set out in Table 5. Using these
bounds, the lower and upper descent rates can be calculated again,
resulting in the bounds presented in Table 6. It can be concluded
from the table that the recorded BFOs indicate that at 00:19:29Z,

Table 6.

MH370 Descent Rates at 00:19Z, 8 March 2014, Under Hypothesis 2
Time Stamp

Min. Desc. Rate,
South Track (fpm)

Min. Desc. Rate,
North Track (fpm)

Max. Desc. Rate,
South Track (fpm)

Max. Desc. Rate,
North Track (fpm)

00:19:29Z

2,900

4,100

5,600

6,800

00:19:37Z

13,800

14,900

16,500

17,600

Min., minimum; Max., maximum; Desc., descent.

IEEE A&E SYSTEMS MAGAZINE

FEBRUARY 2018

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