AIR TRANSPORT
14 | Flight International | 10-16 December 2019 flightglobal.comNone of narrowbody's 62 occupants survived March 2016 accident
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nvestigators believe that soma-
togravic illusion did not trigger
the fatal Flydubai Boeing 737-
accident sequence at Rostov-on-
Don but might have contributed
to a critical error by the aircraft’s
captain.
Somatogravic illusion is the
tendency – in the absence of visu-
al references – to incorrectly per-
ceive acceleration as an increase
in pitch attitude, a perception
that can lead pilots instinctively
to make nose-down inputs even
if the aircraft is flying level.
The 737 (A6-FDN) had been
executing a go-around in dark-
ness as it conducted its approach
to Rostov’s runway 22 on 19
March 2016. It accelerated into a
climb, entering cloud, before
transitioning to a dive after the
captain made nose-down control
column inputs and applied ex-
cessive stabiliser trim.
Russia’s Interstate Aviation
Committee estimated the gravi-
to-inertial forces experienced by
the crew during the go-around to
analyse whether the perceived
pitch deviated from the flight-
data recording of the aircraft's
actual pitch.
While the analysis has limita-PROBE DAVID KAMINSKI-MORROW LONDONNo pitch-up confusion in Flydubai crash
Russian investigators rule out influence of somatogravic illusion on 737 captain attempting landing at Rostov-on-Don
tions, says the inquiry, it never-
theless indicates four “substan-
tial” periods of deviation – with
the gravito-inertial angle greater
than the actual pitch – which
would serve as prerequisites for
the pitch-up illusion.
Official United Arab Emirates
comments to the inquiry ex-
pressed the view that the captain
had fallen under the influence of
this illusion just 2-3s after initia-
tion of the go-around, and that he
remained affected during all sub-sequent actions.
“The investigation team does
not agree with this position,”
says the Interstate Aviation Com-
mittee. “The presence of condi-
tions for the somatogravic illu-
sion is a necessary, but not
sufficient, condition for its actu-
al effect on the pilot.”
It points out that the illusion
tends to manifest itself only once
pilots are out of visual contact
with the horizon or other refer-
ences, and are not adequatelymonitoring instruments. When
the go-around was initiated,
however, the Flydubai 737 was
operating in visual meteorologi-
cal conditions with a cloud base
at around 1,380ft.
With the captain being able to
see both the instruments and the
external environment, it is “high-
ly unlikely” that he would have
been affected by the illusion in
the early stage of the go-around,
says the inquiry.
It adds that analysis of the in-
formation available indicates that
the nose-down column inputs
and the initial use of nose-down
stabiliser trim were probably not
attributable to somatogravic
“pitch-up” illusions.
As the captain applied stabi-
liser trim, for an unusually long
period of 12s, the aircraft transi-
tioned through negative g-forces
into a dive.
This subjected the crew to con-
ditions for the “most intense” il-
lusion, the inquiry says. But it
states that, by this point, the cap-
tain was already “completely
disoriented” and that the poten-
tial impact of any illusion, as op-
posed to the effects of other stress
factors, cannot be assessed. There
is no evidence that the first officer
had suffered spatial disorienta-
tion, it adds.
Investigators have concluded
that somatogravic illusion “did
not have crucial importance” in
terms of the onset of the accident
sequence, although they ac-
knowledge that it “might have
had some impact” on the cap-
tain’s decision to apply nose-
down stabiliser trim for an exces-
sive period of time.
Instead, investigators believe
the captain was psychologically
unprepared for the second go-
around manoeuvre and possibly
suffering tiredness following a
long holding time in the early
hours of the morning.
None of the 62 occupants of
the 737 survived its high-speed
impact with the ground. ■ANALYSISTwinjet could have been saved 6s before impact, says inquiry
Analysis of the Flydubai Boeing
737-800 accident at Rostov-on-
Don shows the aircraft could have
been recovered from its fatal dive
just 6s before impact.
Just 19s before the crash, the
aircraft had been climbing
through 3,350ft with a nose-up
pitch of 10°.
But the captain applied
excessive nose-down stabiliser
trim for about 12s and the aircraft
transitioned to a 40° nose-down
attitude – with its engines
operating at full thrust.
Russia’s Interstate Aviation
Committee has detailed a Boeing
engineering simulation that
aimed to determine the last pointat which the aircraft could have
been saved.
Investigators believe the first
officer was aware of the deterio-
rating situation, and the cockpit-
voice recorder captured him
repeatedly warning the captain,
before suddenly exclaiming: “Pull
it! Pull it!”
The first officer then attempt-
ed to pull the control column,
says the inquiry, with the flight-
data recorder registering a
“momentary” aft control column
input, more than two-thirds off
neutral, before it returned to the
forward position.
“If, at that point in time, the
control column had beenrepositioned to a full pull and
kept at that position, the aircraft
could have been recovered from
the descent with a sufficient mar-
gin of height,” it adds.
This final opportunity to arrest
the dive occurred at 03:41:43,
about 6s before the 737 struck
the ground.
Sustained full aft column input
alone – with no change to trim,
flaps or thrust – would have been
sufficient to allow the jet to re-
cover at 500ft, transition to a
climb and return to normal flight.
The engineering simulation
only took into account the air-
craft’s aerodynamic performance,
and not the state of the pilots. ■