Page 18 - Index

Loss of Control in Flight Event Due to Suspected Icing:
Tailplane or Main Wing Stall?

By Kåre Halvorsen, Senior Accident Investigator, Norwegian Safety Investigation Authority; Michael
Bromfield, Deputy Aerospace Program Director, University of Birmingham, UK; Nadjim Horri, Assistant
Professor in Aerospace, Coventry University, UK; and Knut Lande, Consultant, LandAvia Ltd, Norway

(Adapted with permission from the authors’ technical paper Tailplane or Main Wing Stall? LOC-I Event Due to Suspected Icing accepted for ISASI
2021, a virtual meeting hosted from Vancouver, B.C., Canada, due to COVID-19 restrictions. The full technical paper is posted on the ISASI website at
www.isasi.org in the Library tab under Technical Presentations.—Editor)

n January 2017, a business jet was on aircraft experienced -2.62 g’s during the During the ground stop at Gardermoen,
a short repositioning flight in Norway pitch down upset and +5.99 g’s during the only one engine was stopped while the first
with two pilots on board and no pas- pullout. A tailplane stall due to icing was officer completed an external inspection of
Isengers or cargo. Initially, the takeoff suspected; however, the FDR, being limited the aircraft. He did not observe any ice or
proceeded as normal. As the landing gear to 36 parameters, was not on its own able anything out of the ordinary on the areas
was retracted, the pilots observed that the to confirm this. of the aircraft that could be inspected.
airspeed was rapidly approaching the flap LN-IDB, a Cessna 560 Encore with Serial According to the crewmembers, the
limiting speed of 200 knots. As the flaps Number 560-0637, was manufactured in snow did not accumulate on the wings be-
were retracted at a height above ground 2003. The aircraft type is certified for two fore departure. They could only see melted
level of approximately 2,000 feet, the crew, pilots, captain and copilot. The cabin has water on the wing surfaces and therefore
restrained by their seat belts, experienced room for seven passengers. decided not to deice the aircraft. When the
a violent nose-down pitch motion as the crewmembers requested taxi clearance,
aircraft started banking sharply to the left. The flight they were assigned a different runway than
A full investigation was conducted by the The crew, which consisted of a captain expected. This entailed a longer taxi time
Norwegian Safety Investigation Authority and a first officer, had flown from Bern, and thus longer exposure to the prevailing
(NSIA), supported by industry and aca- Switzerland, to Gardermoen, Norway, with weather conditions. The aircraft’s ground
demic partners. a passenger on board. After disembarking stop lasted approximately 15 minutes at
It is likely that the captain (pilot flying) the passenger at Gardermoen, the aircraft an air temperature of 0 degrees C. The
and first officer (pilot monitoring [PM]) was scheduled to be flown to its home taxiways and runway were covered with 3
experienced different levels of startle and/ base at Sandefjord Airport Torp with- to 6 millimeters of slush, and it was snow-
or surprise during the upset. Control was out passengers on board. The crew had ing when the aircraft took off. After flying
regained at a height of approximately 170 planned to make the ground stop as short from Switzerland for more than 2 hours in
feet above ground level. Data from the as possible, and if the weather conditions approximately -50 degrees C, the aircraft’s
flight data recorder (FDR) showed that the permitted, they would avoid deicing. surfaces (fuselage and wings) were more
than likely chilled.
Initially, the takeoff proceeded as
normal. Figure 2 shows a plot of the most
important parameters retrieved from the
FDR plotted over one common timeline.
The landing gear was retracted, and both
pilots observed that the speed was rapidly
approaching 200 knots, which is the max-
imum speed with flaps deployed. As the
flaps were retracted, the crew experienced
a violent nose-down movement, and the
pilots were “hanging by their seat belts”
while the aircraft started sharply banking
to the left. Following the accident, data
from the FDR showed that the aircraft at
that moment experienced -2.62 g’s.
The captain did not trust the instru-
ments while the first officer (PM) had bet-
ter situational awareness. The first officer
quickly took control and started a pullout
from the dive. The aircraft descended be-
low the cloud base, and even though it was
dark, the pilots could glimpse the ground.
Control was regained, and the aircraft lev-
elled off at 170 feet above the ground. The
aircraft was overstressed to 5.99 g’s during
Figure 1. Cessna 560 Citation Encore LN-IDB (Hesnes Air As).
18 • October-December 2021 ISASI Forum