Page 22 - Index

evator down commands for NSIA Safety Recommen-
varying horizontal tailplane dation Regarding Tailplane
efficiencies were also pre- Icing
sented (see Figure 11, page Safety Recommendation SL No.
22). With 100% efficiency, 2020/01T
the load factor remains very On Jan. 11, 2017, the crew
close to 1 with a small eleva- lost control of a Cessna 560
tor command, as expected. Encore at low altitude after
With 50% tailplane efficien- takeoff. The most probable
cy, the load factor is reduced, explanation for the aircraft’s
but changes are small. Major sudden dive is that the
changes to load factor are, tailplane stalled as a result of
however, obtained with 20% icing from slush spray from
tailplane efficiency and -g is the runway and from falling
quickly reached in this case. snow and sleet. The aircraft’s
This is believed to be closer rubber deicing boots were in
to the conditions experi- automatic mode and inactive
enced during the incident. during the takeoff and when
Figure 10. Long-period oscillation with 80% horizontal tailplane
efficiency. the stall occurred. Textron/
Summary Cessna informed NSIA it had
• Tailplane stall dest- not previously experienced
abilizes the system loss of control as a result of
response. icing on the tailplane on its
aircraft models.
• Flap retraction reduc- NSIA recommends that
es angle attack at the Textron/Cessna inform all
tailplane. its customers that operate
• Flap retraction helps ini- Cessna Citations about this
tially, but not sufficiently accident and about the risk
to stabilize the response of contamination on the
with 20% tailplane tailplane in the form of ice or
efficiency. other substances, which can
result in the tailplane stalling.
• Aircraft pitch response
to elevator commands is
unstable when tailplane Lessons Learned
efficiency is 20%. In the course of this investi-
gation, the following lessons
• Tailplane stall dest- were learned:
abilizes the system • Tailplane icing events are
response. difficult to confirm since
Figure 11. Tailplane stall followed by flap retraction.
The results showed that the evidence might not be
static stability decreases as present (ice accretion).
tailplane efficiency decreas- • Fundamental modeling
es, simulating the onset of effects of icing on
of tailplane icing and that tailplane efficiency can be
increasing up elevator (-VE) used as an alternative to
is required to compensate. complex and costly com-
At low tailplane efficiency, putational fluid dynamics.
the aircraft pitch response
to elevator commands be- • Industry and academic
comes unstable. Flap retrac- collaboration yields bene-
tion initially helps but not fits for both parties.
sufficiently to stabilize the • Industry benefits from
response with low tailplane expertise not always avail-
efficiency, and a tailplane able in house.
stall destabilizes the system • Academia benefits from
response. The safety inves- working on a real-world
tigation authority issued a research problem and
safety recommendation to contributing to knowl-
the aircraft manufacturer, edge.
requesting that it inform
customers about the nature Conclusions
Figure 12. Long-period oscillation with 100% horizontal tailplane of the accident and the risk The aim of this study was to
efficiency. of tailplane stalling. provide further insight into

22 • October-December 2021 ISASI Forum