FAA Warns Pilots Of Part 23 Aircraft
Stall Warning Indicators In Icing Conditions
January 25, 2011- The FAA has issued a Special
Airworthiness Information Bulletin to inform pilots of
normal, utility, acrobatic, and commuter category (part
23) airplanes certificated before 2000 of the potential
hazards associated with stall warning characteristics in
Part 23 contains airworthiness standards for airplanes in the normal, utility, aerobatic, and commuter categories. It dictates the standards required for issuance and change of type certificates for airplanes in these categories.
The Maximum Takeoff Weight of an airplane in the normal, utility or acrobatic category cannot exceed 12,500 lb. The Maximum Takeoff Weight of an airplane in the commuter category cannot exceed 19,000 lb.
has a large number of regulations to ensure airworthiness in
areas such as structural loads, airframe, performance,
stability, controllability, and safety mechanisms, how the seats
must be constructed, oxygen and air pressurization systems, fire
prevention, escape hatches, flight management procedures, flight
control communications, emergency landing procedures, and other
limitations, as well as testing of all the systems of the
determines special aspects of aircraft performance such as stall
speed (for single engine airplanes - not more than 61 knots),
rate of climb (not less than 300 ft/min), take off speed (not
less than 1.2 x Vs1), weight of each pilot and passenger (170 lb
for airplanes in the normal and commuter categories, and 190 lb
for airplanes in the acrobatic and utility categories).
the Federal Aviation Regulations, including Part 23, commenced
on February 1, 1965. Prior to that date, airworthiness standards
for airplanes in the normal, utility and acrobatic categories
were promulgated in Part 3 of the US Civil Air Regulations. Many
well-known types of light airplane are type certificated to CAR
Part 3, even though they remained in production after 1965. For
example, the Cessna 150 and Piper Cherokee are type certificated
to CAR Part 3.
In order to identify precursors to accidents, the FAA studied icing related non-fatal incidents dating back 25 years. The FAA found evidence of stall events during flight in icing conditions on different airplane models in which either the pilot or passenger explicitly stated the stall warning system did not activate.
In some of these
events the pilots attributed ?shudder? or buffet to either the engine or
propeller icing but not an impending wing stall. These reported events
occurred in the cruise phase of flight, in some cases with the autopilot
engaged; during landing approach; and on landing.
Prior to 2000, a
clear and unambiguous buffet was accepted for stall warning in icing
conditions, even if the airplane was equipped with a stall warning
system and a heated stall warning sensor. Prior to 1973, there were no
requirements to test part 23 airplanes in icing conditions. Part 23
airplanes were ?approved? for flight in icing conditions if they were
properly equipped. Many of these airplanes remain in the fleet today.
flight manual, pilot?s operating handbook, and placards should be
consulted for limitations and procedures in icing conditions. The FAA
recommends that you ensure that the following procedures are followed if
not specified for your airplane. Occurrences of buffet or shudder in
icing conditions should be treated as an imminent wing stall. Recover by
reducing angle of attack and slowly applying full power/torque.
airplane flight manual, pilot?s operating handbook, or any placard has
specified an airspeed for flight in icing, increase airspeed by at least
25 percent above non-icing airspeed in every phase of flight. However,
do not exceed any maximum airspeed limitations for your airplane.
The autopilot may
mask dangerous airspeed losses - monitor airspeed closely when the
autopilot is engaged in icing conditions. When ice is accumulating on
the airplane the autopilot should be disconnected at least once every
five minutes to ensure normal airplane trim and handling qualities are
maintained. Unless authorized in the airplane flight manual, the
vertical modes of the autopilot that maintain a constant rate of climb,
decent, or pitch should not be used. Pilots should be prepared for the
possibility of unusual control forces and flight control displacements
when disconnecting the autopilot, especially in severe icing conditions.
If severe icing is
encountered, disconnect the autopilot, and immediately request priority
handling from air traffic control, or declare an emergency if required,
to exit the severe icing conditions. If your airplane was not
certificated to fly in freezing drizzle or freezing rain conditions, do
not fly in these conditions. Do not rely on Automated Surface Observing
System (ASOS) to report freezing drizzle. Know the severe icing cues for
your airplane, such as ice behind the protected leading edge of the
accidents and incidents involving these airplanes have outnumbered those
on icing certificated airplanes in recent years. Pilots of these
airplanes should be aware that these airplanes are not tested for
?inadvertent? icing encounters. Do not believe the myth that ?thicker?
general aviation airplane airfoils are more tolerant of ice accretion.
Pilots of part 23 airplanes are encouraged to report environmental icing related incidents to the Aviation Safety Reporting System. Include the airplane model and other details related to the above recommendations in this SAIB. Under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.), the Office of Management and Budget (OMB) has approved the information collection contained in this SAIB, and assigned OMB Control Number 2120-0731.
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