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Ice Induced Stall Pilot Training


[ Music ] [ Background Voices ] We were going from
Palmdale to Santa Cruz. It was a November day. Routine flight. One we’ve made many times. There was some weather
over the mountains, but it’s an ice-equipped
plane; right? So we got the clearance
for 22,000 feet. But, as we were climbing
through 15, we started today
pick up some ice. At about 15,000 feet we
started to pick up some ice. So we decided to level out
at 16 and try to stay clean. We were completely IMC. We went completely IMC. Air speed was 180 knots. Vertical speed was zero. Prop r.p.m was 1,700. And engine torques
were 1,800 pounds. Auto pilot was engaged
and holding altitude. We were still getting ice,
just a trace at first. But inboard of the nacelle,
where there’s no boot, the ice was starting to show up. We cruised about five minutes
monitoring the ice build-up, cycling the boots as required. Engine instruments looked good. Auto pilot was engaged
and holding altitude. I figured it would
be a smooth ride. I watched the ice build
and cycle the boots. A bunch of ice broke away, but not all of it
cleared completely. Propeller ice would occasionally
shed, hitting the fuselage. It had vibrated on the build-up,
then stopped after the ice shed. It was building on
the wings too. And we were flying a little
more nose high though. I didn’t really realize why. We were flying a little nose
high, but can’t tell you why. I didn’t notice it as a problem. I guess I was dumb and happy. Maybe ready to get home. Suddenly there was a lot
of vibration and buffeting. At first I thought
more propeller ice, but it got more intense. We were thinking
more propeller ice. And at the time neither of us recognized it
as stall buffeting. We advanced the propeller
controls. The props increased. We pushed the props up to
about 2,000 r.p.m. I thought that would help clear
the prop ice. But our problems were
about to get worse. I finally looked at the
air speed, 115 knots. How’d we get there from 180? At the same instant
the left wing dropped. Then the auto pilot
disconnected, and we rolled. We went about 90 degrees. What you have just seen
is based on a true story. A King Air carrying passengers
was flying over the Tehachapis. And through complacency the
auto pilot trimmed the aircraft to stall in icing conditions. This training aid is intended to help pilots understand
the phenomenon of tail plane and wing stall while
flying in icing conditions. The training will also explain
icing certification rules. And it will recommend
cockpit procedures to mitigate ice induced
stall in order to maintain controlled
flight during unexpected icing encounters. Much has occurred since NASA’s
original 1998 ice contaminated tail plane stall video. This film updates that training. Specifically addressing
the reality that for the past 30 years most
icing accidents were caused by wing stall versus tail stall. The FAA wants to
make pilots aware that vigilance is necessary to avoid the low-speed stall
accidents that occur in icing. Especially with the
autopilot engaged. Because of these accidents the
FAA is leading a rule-making effort to both update training for wing stall recognition
and recovery. And to cover procedures while
operating in icing conditions. Pilots need to be
aware that the majority of the general aviation fleet, including previously
icing certified airplanes, may not be certified to
the latest standards. This means that an
airplane’s susceptibility to ice-contaminated tail
plane stall may not be known. It also means that the stall
warning system may not activate prior to wing stall
in the icing. In order to revise icing
certification standards, the FAA has searched
icing-related nonfatal incidents dating back 25 years for
precursors to accidents. And has found evidence of
stall events during flight in icing conditions in which
the stall warning system did not activate. This was found on many
different airplane models. Ice-induced stall has
occurred in cruise, on approach and during the landing
phase of flight. In some of these events the
pilots attributed shudder or buffet to turbulence, engine
roughness or to propeller icing. But not to an impending
wing stall. The FAA believes that
many icing incidents and accidents follow
a similar path. I finally looked at the
air speed, 115 knots. How did we get there from 180? At that same instant
the left wing dropped. We went about 90 degrees. My recollection is to the
right, but it was to the left. The artificial horizon
was half blue, half black. The directional gyro
showed us turning. I pushed the yoke forward
and applied maximum power and worked the rudder. Just a tiny sliver of
blue crescent was visible. And the blue slowly moved up. The gyro showed us turning. The vertical speed indicator was down about 3,000
feet per minute. I expected to feel
G’s but didn’t. And no stall horn. I thought maybe the
stall horn had iced over or maybe the ice covered
wing didn’t trigger the horn. Either way it didn’t sound. I’m not exactly sure when we
recovered, but the ice cleared at just below 11,000 feet. And we leveled out at 10. Must have been warmer
below, so I got control of the plane at about 11,000. And leveled out at 10. I apologized to the
passengers for the excitement and attributed it to prop icing. But I know now that we had
a wing stall due to ice and complacency, my complacency. I don’t know how I missed it. You’d expect that it
could manage a little ice, but it didn’t. Not that day. A pilot hearing about icing
encounters may be left asking, how can an airplane stall
without any stall warning? Or how does an airplane equipped
with ice protection systems get into trouble during
icing conditions? Or even, why is the pilot flying
into an icing cloud at all? The simple answer
is icing happens. And sometimes, when all
precautions are adhered to, an icing encounter
is unavoidable. Before describing the
effects of ice on wing stall, it may be helpful to explain
how small airplanes have been certified for flight in icing. Prior to 1973, small airplanes
and turbo prop airplanes with boots were approved
for flight in icing if they were equipped
with a minimum suite of ice protection equipment. No actual testing in icing
conditions was required. According to the certification
standards of that time, the airplane could be
flown in light icing, but had to limit time
in moderate icing. Many of these airplanes
remain in the fleet today, operating under parts
91 and 135. The icing certification on
other models was removed via air worthiness directives based on their adverse
icing service history. [ Music ] After 1973, airplanes had to
demonstrate safe operation in cloud icing conditions. These conditions are known as
Part 25 Appendix C conditions. Safe operation, however,
was not defined until 1993, when the small airplane
certification rules were amended once again. Your AFM is the best source
for you as a pilot to determine if your aircraft is
certified for or prohibited from flight into known icing. But your AFM won’t tell
you what testing was done. Or what certification standards
your plane was built under. Even if your aircraft is
brand new, don’t assume that it has been tested to
the most current standards. If the aircraft type was
certificated under CAR 3, then the standards of that
certification are the ones met by that aircraft, even when you
buy a brand new plane right off the line. Susceptibility to ice contaminated tail
plane stall was not tested on new icing certified
airplanes until 1994. From 1973 until the
year 2000, a clear and unambiguous buffet
was accepted for stall warning
in icing conditions. Even when the airplane
was equipped with a stall warning system and
a heated stall warning sensor. It wasn’t until the year 2000
that stall warning systems, if installed, were shown to
provide adequate stall warning with critical ice along the
entire span of the wing. This animation shows how ice
often affects the coefficient of lift for an airfoil. When flying at cruise speeds
at very low angles of attack, ice on the wring may
have little effect on the coefficient of lift. However, pilots should be aware
that the maximum coefficient of lift can be significantly
reduced by the ice and the angle of attack at which it occurs. Which means the stall
angle is greatly reduced. So, when slowing down, the pilot
may find that ice on the wing, which had little effect on lift
in cruise, now causes stall to occur at a significantly
lower angle of attack and higher air speed
than a non-iced wing. Ice that accumulates on
pneumatic deicing boots or between boot cycles,
called residual ice, can increase stall speed
significantly as well. It doesn’t matter what type
of wing airfoil you have. Recent certification work shows that the stall speed can
increase by as much as 20 knots for a typical small airplane, even with a certified
ice protection system. These stall curves show that the
stall warning system would have to annunciate at a substantially
lower angle of attack to function effectively
in icing conditions. The stall warning
systems do this on airplanes certified
after the year 2000. Pilots should also
note that with ice on the wings a heated
stall warning vane by itself does not ensure that adequate stall warning
will be provided to the pilot. One of the first signs of
performance degradation caused by ice is an increase in drag. This can be observed during
cruise by a need for more power than is typically used
for a particular speed. An increase in drag will also
decrease climb performance. Because no requirements
for climb performance in icing conditions
existed prior to 1993, icing accidents involving
small airplanes, especially those not
certified for flight in icing, were often caused by a wing
stall while trying to climb out of icing at altitudes
above 10,000 feet. This is still an issue today. [ Music ] Another way icing can
affect the aerodynamics of an aircraft happens
when ice forms on a horizontal stabilizer, triggering the loss
of lift at the tail. Back in 1995 through 1997, NASA did a tail plane icing
program using a Twin Otter. Which resulted in a
tail plane icing video that this training
video replaces. A follow-on program in 2001
was done on a Twin Otter, which investigated both the wing
and tail stall by application of ice shapes on both the
wing and tail leading edges. This was a great
opportunity for me. On the same flight I was able to
experience both types of stalls and the recovery techniques. While we describe the
tail stall phenomena in this training video,
we’ve learned that since about the year 2000
that tail stalls within the current
operating fleet are very rare. Still, for those airplanes
that may be susceptible, it is important to
understand the difference between a wing and tail stall. And when you might
expect them to occur. This animation illustrates
the tail stall phenomenon. The center of gravity of an airplane is
almost always forward of the wing’s center of lift. The forces acting at these
two points cause a nose-down pitching moment, which
must be counteracted by the horizontal tail. When the flaps are extended, several things happen
simultaneously. The wing center of
lift moves aft, creating a larger
nose-down pitching moment that the horizontal
stabilizer must overcome. The tail angle of
attack increases. This is due to the
increased wing down wash which naturally generates more
downward lift by the tail. Consequently, the flap extension
drives the horizontal stabilizer closer toward its
stalling angle. On some airplanes
application of full power when the flaps are deployed
can also induce tail stall. Symptoms on most
airplanes may be subtle. A lightening of the
controls may be felt. There may also be difficulty
trimming the airplane. Pilot induced oscillations
may be experienced. If these symptoms
are experienced after the flaps have been
fully deployed and there is ice on the airplane, a tail stall is
eminent the pilot should firmly hold the yoke to
prevent a pitchover. And then gradually raise
the flaps to a setting and manage speed to where
these symptoms are not present. Land with reduced flap setting
if permitted within AFM. If the tail fully stalls, there will be a sudden
forward stick pulse, possibly very strong. The nose of the aircraft
will suddenly pitch down. In this extreme case
the corrective action is to pull the yoke back
enough to regain control of the pitch attitude,
reduce flap setting and on some aircraft
ease off on power. This recovery is the
opposite of a wing stall. So it is absolutely
critical to sense the cues, know the airplane
configuration and speed to distinguish a wing
stall from a tail stall. And then perform the
right corrective action. Remember full flap or near
full flap deflection is needed to cause a tail stall. If flaps are not deployed, you are not experiencing
a tail stall. Since 1994, all new icing
certified aircraft have been tested for ice-contaminated
tail plane stall susceptibility. Many have been shown
to not be susceptible. In those airplanes
that were susceptible, tail plane stall occurred only
with full-flap deflection. Or with full-flap deflection
combined with takeoff power. In those cases operational
limitations were placed in the AFM to ensure
safe margins. In these airplanes you must
follow your AFM limitations and procedures on maximum
flap setting in icing. [ Music ] To manage icing situations
properly, you must determine if your airplane
has been evaluated for ice-contaminated
tail plane stall. If you are a commercial
operator, contact your principal
operations inspector. They have access to a proprietary database
containing this information as described in FAA
notice 8900.267. If you are a general aviation
pilot, look up your airplane on the type certificate data
sheet or TCDS on the FAA website at www.faa.gov to determine when
your airplane was certified. If your airplane was
certified prior to 1994, unless it was modified after
1994 to add icing certification, you can assume that
it was not evaluated for ice-contaminated
tail plane stall. Contact your airplane
manufacturer for additional information. The FAA has made the following
recommendations for flying in icing conditions based
on NASA tail stall research and on years of certification
flight test experience on numerous airplane models. If your airplane
has been evaluated for ice-contaminated tail plane
stall certified after 1994, follow the AFM limitations
and procedures. Paying attention to maximum
flap settings, if any. And to minimum speeds
for icing conditions. When doing this, there is no
ice-contaminated tail plane stall to worry about. You should treat buffet
as impending wing stall. And perform wing stall
recovery procedures that include lowering the nose. Treat un-commanded motion
or control anomalies as impending wing stall. And perform wing stall
recovery procedures that include lowering the nose. Treat any stall warning system
annunciation as wing stall. Recovery should emphasize
a reduction in wing angle of attack. If your airplane has
not been evaluated for ice-contaminated
tail plane stall, assume this if your airplane was
certified in 1994 and earlier. Treat any stall warning system
annunciation as a wing stall. If the field length permits,
land with flaps less than full. If your AFM has no
minimum speeds for icing, increase your speed
by 15 percent to account for ice accretion. Check and use your manufacturer
recommended approach speeds for using less than full flaps. Estimate that your landing
distance will increase by 30 percent for every
15 percent increase in landing speed. Treat un-commanded motion or control anomalies
as a wing stall. If you must land with full flaps or with a tail ice
protection system failure, treat buffet either
as a wing stall or tail stall using the
following guidelines. Noting that air speed
awareness is critical, slow equals wing stall. Configure early an approach to provide recovery
margin should it be needed. If auto pilot is engaged,
check your air speed. It is most likely a wing stall. If you are maneuvering and there
is no recent full flap extension or maximum power increase, it
is most likely a wing stall. If you experience a
loss of lateral control or roll oscillations, it is
most likely a wing stall. If you just extended
flaps to full settings or you just applied
maximum power with flaps at full settings and you
experience an un-commanded pitch down or an apparent loss or
reduction of pitch control, you are most likely
experiencing tail stall. Apply tail stall
recovery procedures. On airplanes with stick pushers, remember the stick
pusher activation looks like an un-commanded pitch down, but still indicates
a wing stall. Air speed awareness is critical. Slow equals stall. If you must climb to
exit icing conditions, fly at or above your airplane’s
minimum air speed for icing. Don’t rely on the stall
warning to keep you safe. Consult your AFM limitations
under procedures and performance for climbing in icing
conditions. If there are no limitations
for climbing, consider the climb
performance of the airplane and the minimum vectoring
altitude when determining your route. Plan for exit strategies
during your preflight planning. Don’t assume you can climb
with ice on your airplane. Climb performance is degraded, sometimes significantly
in icing conditions. Only consider climbing
when ice first starts to build up on the airplane. Otherwise, descend to
get out of the ice. Never fly below the
minimum air speed in icing. If you can’t maintain at
least the minimum air speed in ice during a climb, then
stop the climb right away. And initiate a descent to
exit the icing conditions to maintain your air speed. If you ever find
yourself in a position where you can’t maintain the
minimum air speed in icing, begin a descent and
trade altitude for air speed to avoid a stall. If you’ve made a request
to climb, descend or turn to exit ice and there’s
an ATC delay, request an immediate climb
or descent in any direction. And express your need to
exit the icing conditions. Don’t hesitate to declare
an emergency if the safety of flight is in question. If you have just entered a cloud
and encounter icing conditions, make a 180-degree turn,
if possible, to exit. Above all, maintain
your air speed above minimum air speed in ice. And don’t hesitate to declare
an emergency if needed. Going back to the pilots’
story at the beginning of this training, you may have
noticed that the auto pilot was on and holding altitude. But this was at the
expense of air speed as ice accumulated
on the airplane. Pilots of small airplanes,
particularly when flying alone, should use the auto
pilot if installed. But all pilots should
periodically disconnect the auto pilot in significant icing
to check controllability. The pilot must also be vigilant
and monitor air speed closely. The FAA is aware of one
severe icing encounter with a small turbo-prop powered
airplane in which 50 knots of air speed was lost in
a little over a minute. When climbing in icing, do not use the vertical speed
mode unless explicitly allowed by the AFM. Pilots of icing certificated
aircraft should not be casual about operations in
icing conditions, particularly extended
operations. You may encounter
an unusual condition for which your aircraft
has not been certificated. Such as liquid water content
outside the envelopes. This is sometimes indicated by a
very rapid rate of accumulation. And can result in run
back and ice build-up aft of the protected surfaces. Another more common
icing conditions that airplanes have
never been certified to is super cooled
large drop or SLD. Otherwise known as freezing
drizzle and freezing rain. These large drops can form
ice farther aft on surfaces, resulting in larger
lift and drag penalties. Ice that forms aft of the leading edge protected
area is severe icing. You must avoid these conditions, starting with your
preflight planning. Do not rely on METARs
at airports with no human weather observer
to report freezing drizzle or any freezing precipitation
when snow is falling. [ Music ] In 2014, the FAA published
a new certification rule for transport category
airplanes. New transport airplanes
will have to show that they can safely
operate in SLD or show that they can detect
and safely exit SLD. As of 2015, there is a
similar rule-making effort for small airplanes. After viewing this film, you know that pilots
must never be complacent in any icing encounter. The pilots in our opening story
successfully managed their flight during icing. But the next icing
cloud they fly into may bring different
hazards. Each icing encounter is unique. Effectively planning for a safe
flight during icing conditions begins on the ground. And should include
the following steps. Check for icing conditions
during preflight weather. Know where and when
icing may occur. And plan your route to avoid it. Know your airplane’s
icing certification. Know whether or not your
plane is susceptible to ice-contaminated tail stall. Consult the date of
certification in the TCDS on the FAA website or your
airplane manufacturer. In any inadvertent
icing encounters work to get out immediately. Assume higher stall speed,
degraded climb performance and sacrifice altitude
for air speed. Remember to keep your air speeds
up, even if it’s necessary to descend to do this. If your AFM has minimum
speeds for icing, follow them. If the AFM has no minimum
speeds, increase speeds by at least 15 percent. Periodically turn off auto
pilot to check for control. If you experience
shudder or buffet, it is probably wing stall. Recover by first pushing forward
to lower angle of attack. On approach and landing,
increase speed and use partially
extended flaps. Or follow the recommendations
in your AFM. Activate your ice protection
in accordance with your AFM. This is critical on many
airplanes certified since 2000. Because activating your
ice protection system bumps up your stall warning speed. Since the workload on
approach may be high, consider activating your
ice protection system when configuring for approach if there is any possibility
of icing. In your preflight planning, remember the higher
operating speeds for icing increase
runway length. And your AFM may have
lower weight limits. Inadvertent ice encounters
happen. Pilots who inadvertently
encounter icing in non-icing certified
airplanes can also benefit from the recommendations
in this video. In any ice encounter, the most
important thing is to be aware. Cross check air speed, power
setting with instruments and airplane attitude. If you observe changes in any of these parameters,
respond accordingly. If you don’t know, find out. Determine if and when your
airplane was certificated. Check your AFM for limitations
and procedures in icing. If your AFM has none, follow
the procedures in this training. Start your awareness
in preflight weather. Know where the freezing
level in cloud tops are. Be aware of your
climb performance, and that it will be
reduced in icing. Be vigilant of your air speed
when in icing conditions. When climbing. During cruise. And during approach and landing. If the cruise air
speed continues to decrease while
maintaining a level altitude and requires continually
increasing power, it is time to consider
a descent. Do not let air speed decrease
unabated without pilot action. Remember, when you’re
in ice, work to get out. If you experience stall, remember that most
are wing stalls or should be treated that way. Wing stall recovery must start
with pushing forward on the yoke to lower angle of attack while
trading altitude for air speed. Maintaining control
of the airplane at all times is an
absolute necessity. And off-field control
landing is better than an uncontrolled crash. Speed is life. [ Music ]

Reynold King

14 Replies to “Ice Induced Stall Pilot Training”

  1. Really good video!

    Having flown quite a few different types small planes often in IMC and often in ice, there is a serious difference in behavior from one model to another. Some planes handle ice well, other begin flying like a brick.

    Some planes with boots are pretty tame, others not so much…….

    This is why you need to be paying extra attention especially if you're not familiar with a particular aircrafts behavior in ice.

  2. Anti-ice clears ice where the anti-ice system heats or flexes the surface. (within the capability of the equipment)

    There is a LOT of surface that has no means of forcing the ice to shed. Ice = weight and drag and disrupted airflow.

    I'd ask for different altitude if the plane is cycling accumulating and shedding ice on the prop…. That is a big sign you need to get somewhere colder or warmer.

  3. Thank you for sharing this great training video for free. I know you doing it in the name of safety (and thus in your own interest of reputation in the long run), but it is also a valuable resource for pilots outside of the USA. Sharing this to literally the world is so valuable.

  4. Air Disaster: Episode- Murder in the sky
    Is it possible for AI to recognize when a murder / suicide has happened in the cockpit and automatically takeover the plane to land it safely? Maybe an FAA official could send a signal to plane to turn the computer on to takeover the plane?

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