Page 23 - Index

LOC-I/upset events in icing conditions.
The main objective was to identify the
probable characteristics of an LOC-I/upset
event due to tailplane icing for a generic
business jet. The lack of available stabil-
ity, control, and aerodynamic data for a
specific aircraft make/model resulted in a
generic business jet model being used for
all analyses. Therefore, it has not been pos-
sible to replicate exact aircraft dynamics
as evidenced by FDR data using modeling
and simulation techniques. Flight data
analysis and weather reports were used to
determine flight conditions to be assessed.
Static and dynamic stability was assessed
using established flight dynamics theory
and modeling.
The modeling and “what-if” trends anal-
ysis does, however, illustrate similar trends
to the recorded flight data, particularly
in the case of a severe tailplane stall. The
degradation/severity of tailplane aero-
dynamic characteristics due to icing was Figure 13. Dynamic pitch stability with varying tailplane efficiency.
simulated using an assumed reduction in
the tailplane efficiency factor and classical
theory supported by a commercial aircraft
design software package.
The results are applicable only for short
periods of time after a given disturbance
since
• a linearized flight model was used
around a trimmed flight condition.
• no pilot control inputs were available
(e.g., yoke pitch/roll, rudder).
• no external (environmental) dis-
turbance data was available (e.g.,
turbulence).
The results demonstrate that the generic
business jet aircraft used in the analysis
is statically and dynamically stable when
horizontal tailplane efficiency is high.
When horizontal tailplane efficiency is
reduced (simulating a “tailplane stall”),
the aircraft is statically and dynamically
unstable. Smaller and shorter elevator
commands produce large pitch responses, Figure 14. Load factor with varying tailplane efficiency.
and -g may be quickly reached within a in which the evidence is not present for • the incident underscores the
short period of time. sufficiently improving the safety can be deficiency of the pneumatic boot
As with most incidents and accidents, easily overlooked. deicing systems.
there are multiple contributing factors. This incident has several lessons Internationally, the International Civil
NSIA has determined that a probable learned, the most important being Aviation Organization’s Annex 13, and
explanation for the aircraft’s sudden dive • tailplane stall due to icing is a real within Europe EU Regulation 996/2010,
is that the tailplane stalled as a result of threat. gives rights and responsibilities for
icing caused by contamination from slush • tailplane stall due to icing is a well- involved parties. Any safety investigation
and spray from the runway and/or from known cause for accidents during involves teamwork and benefits from
falling sleet and snow. Was this an infre- icing conditions. also bringing universities and similar
quent, one-of-a-kind (“black swan”) event? • the incident highlights the impor- academic environments with their
Possibly not. From an NSIA perspective, tance of deicing before takeoff in icing know-how and equipment into the safety
less frequently reported incidents or those conditions. investigation.

October-December 2021 ISASI Forum • 23