Three Incidents Found In Which Ice Restricted Rudder
Travel
The NTSB is investigating three incidents involving Cessna
Aircraft Company (Cessna) 560XL airplanes that experienced loss of
rudder control after ice built up inside the tailcone. Preliminary
findings indicate that water can collect inside the tailcone and
then freeze around and restrict the movement of the rudder boost
cables and pulleys. As long as the frozen ice impedes the cables
and pulleys, the pilot may be unable to deflect the rudder, which
is particularly dangerous when attempting to land in a crosswind or
maneuver on the runway. Normally, a pilot would not use the rudder
during cruise flight and would not detect that the rudder was
frozen until just before or after landing.
Although the investigations are ongoing, the information
gathered to date has raised serious concerns about the potential
loss of rudder control when ice builds up inside the tailcone. The
board believes this matter warrants action by the FAA.
On December 1, 2010, about 1336 eastern standard time, a Cessna
560XL, N607QS, experienced a jammed (unresponsive) rudder during
landing at Toledo Express Airport, near Toledo, Ohio. The two
pilots and one passenger were not injured, and the airplane
sustained no damage. The nonscheduled, domestic passenger flight
was conducted under 14 Code of Federal Regulations (CFR) Part 135.
Visual meteorological conditions prevailed at the time of the
accident, and the flight was operating on an instrument flight
rules flight plan.
NTSB Photo
During the approach to landing, the pilot disengaged the yaw
damper about 600 feet above ground level. He then experienced a
jammed rudder as he tried to align the airplane’s flightpath
with the runway’s centerline during the flare. The pilot
stated in writing to the NTSB that “the rudder pedals were
hard…. I actuated the autopilot disconnect button three
times in rapid succession in case the [yaw damper] was still
connected. No effect.” The pilot further stated that, when he
applied the rudder pedals, the rudder would not move. The pilot
reported that he received no other indications, such as changes in
handling qualities, that the rudder was not operating normally. The
pilot stated that, after landing, he was able to slow and maintain
directional control of the airplane only through differential
braking (that is, asymmetrical application of the main landing gear
brakes).
FAA inspectors examined the airplane at a fixed-base operator
(FBO) and found that ice had formed at the bottom of the tailcone
and around the rudder boost cables and pulleys in the tailcone.
On December 13, 2010, about 0657 central standard time, a Cessna
560XL, N498AB, experienced a jammed rudder during its landing at
Birmingham-Shuttlesworth International Airport, near Birmingham,
Alabama. The pilots and passenger were not injured, and the
airplane sustained no damage. The nonscheduled, domestic passenger
flight was conducted under 14 CFR Part 135. Visual meteorological
conditions prevailed at the time of the accident, and the flight
was operating on an instrument flight rules flight plan. A
postincident examination inside the airplane’s tailcone
revealed ice around the rudder boost cables and pulleys.
NTSB Photo
On December 20, 2010, about 1909 mountain standard time, a
Cessna 560XL, N626QS, also experienced a jammed rudder during
landing at Idaho Falls, Idaho. The pilots and passenger were not
injured, and the airplane sustained no damage. The nonscheduled,
domestic passenger flight was conducted under 14 CFR Part 135.
Marginal visual meteorological conditions prevailed at the time of
the accident, and the flight was operating on an instrument flight
rules flight plan. The initial flight crew discrepancy report
indicated that the rudder was jammed during landing and that
further operations were conducted with differential braking. After
about 15 minutes, the pilots verified that the rudder was again
operational.
Per 49 CFR 830.5(a)(1), the operator reported this incident to
the NTSB. The data was collected, but the operator’s
maintenance crew could not verify the presence of ice in the
tailcone, and rudder operation returned to normal.
According to Cessna, water can enter the Cessna 560XL tailcone
through a large opening at the top of the tailcone where the rudder
torque tube passes into it. In order to prevent water from
accumulating in the tailcone, Cessna, on April 21, 2005, issued
service letter (SL) 560XL-53-05, which requested that all operators
drill a 0.201-inch-diameter drain hole in the bottom of the
tailcone. However, while in flight, low pressure develops across
the tailcone; the pressure differential across the drain hole is
sufficient to draw water into the tailcone and also prevents water
from draining. The water can then collect during flight and can
rise to the level of the rudder boost cables and pulleys,
potentially freezing around the cables and pulleys, as seen in
figure 2. When the water freezes, the motion of the rudder boost
cables and pulleys is restricted.
For the Cessna 560XL airplane involved in the December 1, 2010,
incident, maintenance records indicate that a hole had been drilled
in the tailcone. However, when the FAA personnel examined the hole
postincident, it measured 0.182 inch, which was smaller than the
0.201-inch diameter required by the SL. Three other Cessna 560XL
airplanes were at the Toledo FBO after the December 1, 2010,
incident. FAA personnel examined these three airplanes and found
that holes smaller than 0.201 inch were present in these
airplanes’ tailcones. Both the December 13, 2010, and
December 20, 2010, incident airplanes had the correct
0.201-inch-diameter hole (as required by SL 560XL-53-05), according
to FBO and operator maintenance personnel, respectively.
All three Cessna 560XL incident airplanes likely had ice in
their tailcones. Because the December 13 and 20, 2010, incident
airplanes had the correct 0.201-inch-diameter hole in their
tailcones and still collected moisture that froze around the
rudder’s boost cables, it is evident that a tailcone hole
that complies with SL 560XL-53-05 is not sufficient to adequately
drain moisture and may allow water to enter the tailcone during
flight.
The NTSB understands that Cessna has developed a modification to
address the problem of water collecting in the tailcone area. SL
560XL-53-08 asks operators to, within 90 flight hours or 90 days
from the date of receipt, drill a 0.75-inch-diameter hole in the
bulkhead in the aft fuselage frame, slightly above the lower edge
and below the holes for the rudder boost cables. This hole would
drain any water from the tailcone into the fuselage before the
water level could become high enough to freeze around the rudder
boost cables or pulleys. SL 560XL-53-08 also proposes that
operators seal the drain hole in the tailcone, if one exists.
A pilot may not detect that water has collected and frozen in
the tailcone until he needs to use the rudder to align the airplane
with the runway for landing or to maneuver while at high speed
during the landing rollout. Thus, the risk associated with the
accumulation of ice can lead to an accident because the pilot may
not be able to prevent the airplane from exiting the runway at high
speed. Further, in the event of an engine failure, the use of the
rudder to maintain directional control is crucial at any time.
Thus, it is critical that operators take specific action to ensure
that ice does not form inside the tailcones of Cessna 560XL
airplanes. The NTSB concludes that a drain hole between the
tailcone and fuselage would provide a path for water to exit the
tailcone before freezing.
Therefore, the NTSB recommends that the FAA:
Issue an airworthiness directive to require that all Cessna 560XL
operators comply with Cessna service letter 560XL-53-08.
(A-11-16)