[Federal Register Volume 65, Number 247 (Friday, December 22, 2000)]
[Notices]
[Pages 80984-80986]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-32526]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration


Definition of Terms Applicable to In-Flight Icing Events

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of intent.

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SUMMARY: This document contains proposed definitions of inflight icing 
terminology to be used by the FAA and other aviation related entities. 
Some commonly used terms have been changed for clarification. One term 
was eliminated from official usage while others have been introduced 
for the first time in order to meet the requirements of a changing 
technological environment. The FAA solicits public comment on these 
proposed definitions.

DATES: Send your comments on or before January 22, 2000.

ADDRESSES: Address your comments to the Docket Management System, U.S. 
Department of Transportation, Room PL401, 400 Seventh Street, SW., 
Washington, DC. You must identify Docket Number FAA-2000-8560 at the 
beginning of your comments.
    You may also submit comments through the Internet to http://dms.dot.gov. You may also review the entire public docket for this 
notice at that same site. You may also review the public docket in 
person in the Docket Office between 9 a.m. and 5 p.m., Monday through 
Friday, except Federal holidays. The Docket Office is on the plaza 
level of the Department of Transportation.

FOR FURTHER INFORMATION CONTACT: Daniel Meier, Flight Standards 
Service, Federal Aviation Administration, 800 Independence Avenue, SW, 
Washington, DC 20591; Telephone: (202) 267-3749.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Anyone may participate in this proposal by providing such written 
data, views, or arguments. Identify the regulatory docket and submit 
your comments to the DOT Rules Docket address specified above.
    The FAA will file all comments received, as well as a report 
summarizing each substantive public contact with FAA personnel on this 
rulemaking. The docket is available for public inspection before and 
after the comment closing date.
    The FAA will consider all comments received on or before the 
closing date before we take action on this proposal. We will consider 
comments received late as far as possible without incurring expense or 
delay.
    If you want the FAA to acknowledge receipt of your comments, 
include a pre-addressed, stamped postcard with those comments. On the 
card write ``Comments to Docket No. FAA-2000-8560.'' We will date stamp 
the card and mail it back to you.

Availability of This Notice

    You can get an electronic copy of this notice from the docket with 
the following steps:
    (1) Go to the search function of the Department of Transportation's 
electronic Docket Management system (DMS) web page (http://dms.dot.gov/search).
    (2) On the search page, type in the last four digits of the Docket 
number shown at the beginning of this document. Click on ``search''.

[[Page 80985]]

    (3) On the next page, which contains the Docket summary information 
for the Docket you selected, click on the notice.
    You can also get an electronic copy using the Internet through the 
Federal Register's web page at http://www.access.gpo.gov/su_docs/aces/acrs140.htm.
    You can also get a copy of this notice by mail by submitting a 
request to the Federal Aviation Administration, at the address given 
under for FOR FURTHER INFORMATION CONTACT.

Background

    Following the icing conference of 1996 the FAA devised a plan to 
accomplish the recommendations and concerns which arose from that 
conference. To satisfy one of its responsibilities under the in-flight 
Icing Plan, the FAA undertook the task of clarifying and redefining 
icing terminology applied to in-flight operations. The FAA was to: 
First, ensure that this icing terminology (e.g., known, forecast, 
observed, trace, light, moderate, severe, and ``Appendix C'' icing) is 
used consistently and clearly by the Flight Standards Service, pilots, 
dispatchers, the National Weather Service (NWS), Aviation Weather 
Center, the Aircraft Certification Service, and Air Traffic; and 
second, to update guidance related to icing reporting and pilot, Air 
Traffic Control, and dispatcher actions.
    To accomplish these objectives the FAA established the Task 1B 
working group (WG) which comprised representatives from FAA, National 
Oceanic and Atmospheric Administration (NOAA), and the University 
Corporation for Atmospheric Research (UCAR). The goal of the WG was to 
review the definitions of all icing-related terms that appear in 
government aviation regulations, weather-related handbooks, aircraft 
flight manuals, etc. Based on its findings, the WG was to make 
recommended changes to the definitions where they needed to be updated 
or improved. These recommendations would endeavor to eliminate 
misunderstanding in their use among and between the previously 
mentioned sources.
    This work was accomplished through a series of meetings by the WG, 
and the result was a set of proposed definitions for in-flight icing 
terminology. The WG did not consider or propose any changes to the 
aviation regulations or icing forecasting procedures, although it 
became clear to the WG that existing regulatory wording and existing 
policy within the U.S. National Weather Service (NWS) and the 
International Civil Aviation Organization (ICAO) limited the freedom of 
the WG to change the icing-related terms in use.

Discussion

    The following is a list of terms recommended by the Task 1b 
terminology sub-committee as an updated replacement for current 
terminology used in reference to in-flight icing of aircraft. The FAA 
intends to update the current terminology with the following proposed 
terms that the FAA is presenting, in this publication, for public 
comment. The term ``trace ice'' has been eliminated from the in-flight 
icing vocabulary. The definition of trace ice implied that it was not 
hazardous to flight, however, experience and research have shown that 
trace ice can be hazardous in certain conditions. It follows therefore 
that if trace ice can be hazardous, then light and moderate icing 
intensity can also be hazardous. Additionally, eliminating the term 
``trace ice'' complies with NTSB recommendations A-98-88 which states: 
``Amend the definition of trace ice contained in Federal Aviation 
Administration (FAA) Order 7110.10L, ``Flight Services'' (and in other 
FAA documents as applicable) so that it does not indicate that trace 
icing is not hazardous.''

Proposed Definitions

Light \1\
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    \1\ A representative accretion rate for forecasting or reference 
purposes is \1/4\ inch in 15 minutes to an hour on outer wing or 
tailplane (prior to activation of any ice protection equipment).
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    The rate of ice accumulation may require occasional use of ice 
protection systems to remove/prevent accumulation.

Moderate \2\
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    \2\ A representative accretion rate for forecasting or reference 
purposes is \1/4\ inch in 5 to 15 minutes to an hour on outer wing 
or tailplane (prior to activation of any ice protection equipment).
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    The rate of ice accumulation is such that frequent use of ice 
protection systems is necessary.

Severe \3\
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    \3\ A representative accretion rate for forecasting or reference 
purposes is \1/4\ inch in 15 minutes to an hour on outer wing or 
tailplane (prior to activation of any ice protection equipment.
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    The rate of ice accumulation is such that ice protection systems 
fail to remove the accumulation of ice.

    Note: Ice types are not used in forecasting or pilot reports and 
have no relevance as to effects on an airplane in flight. They will 
be removed from the AIM, but for other purposes the following 
definitions are proposed for inclusion in the AIM.)

Rime Ice

    A rough, milky, opaque ice formed by the instantaneous freezing of 
supercooled water drops as they strike the aircraft. The fact that the 
droplets maintain their nearly spherical shape upon freezing and thus 
trap air between them gives the ice its opaque appearance and makes it 
porous and brittle.

Glaze Ice

    A coating of ice, sometimes clear and smooth, but usually 
containing some air pockets which result in a lumpy translucent 
appearance. Glaze ice results from supercooled liquid water striking a 
surface but not freezing instantaneously on contact. Glaze ice is 
denser, harder and sometimes more transparent than rime ice. Factors, 
which favor glaze formation, are those that favor slow dissipation of 
the heat of fusion (i.e. slight supercooling and rapid accretion).

Clear Ice

    A glossy, transparent ice formed by the relatively slow freezing of 
supercooled water droplets.

Mixed Ice

    Simultaneous appearance or a combination of rime and clear ice.

Known or Observed/Detected Icing

    Actual ice observed visually on the aircraft by the flight crew, or 
identified by on-board sensors.

Forecast Icing Conditions

    Environmental conditions expected by the approved weather service 
to be conducive to the formation of in-flight icing on aircraft.

Potential Icing Conditions

    Atmospheric conditions conducive to ice accretion on aircraft 
components. Visible moisture and temperatures colder than a specific 
temperature typically define these conditions. The aircraft 
manufacturer normally defines these conditions.

Known Icing Conditions

    Atmospheric conditions in which the formation of ice is observed or 
detected in flight. (Note: Because of the variability in space and time 
of atmospheric conditions, the existence of a report of known icing 
does not assure the presence or intensity of icing conditions at a 
later time, nor can a report of no icing assure the absence of icing 
conditions at a later time.)

[[Page 80986]]

Freezing Rain (FZRA)

    Rain is precipitation on the ground or aloft in the form of liquid 
water drops which have diameters greater that 0.5mm. Freezing rain is 
rain than exists at air temperatures less than 0 degrees C, remains in 
liquid form, and freezes upon contact with objects on the surface or 
airborne. While the temperature of the ground and glazed objects 
initially must be near or below freezing, it is necessary that the 
water drops be supercooled before striking. When encountered by an 
aircraft in flight, freezing rain can cause a dangerous accretion of 
icing.

Freezing Precipitation

    Freezing precipitation is freezing rain or freezing drizzle.

Freezing Drizzle (FZDZ)

    Drizzle is precipitation on the ground or aloft in the form of 
liquid water drops which have diameters less than 0.5mm and greater 
than 0.05mm. Freezing drizzle is drizzle that exists at air 
temperatures less than 0 degrees C, remains in liquid form, and freezes 
upon contact with objects on the ground or airborne. While the 
temperature of the ground surface and glazed objects initially must be 
near or below freezing, it is necessary that the water drops be 
supercooled before striking. When encountered by an aircraft in flight, 
freezing drizzle can cause a dangerous accretion of icing.

Icing in Precipitation

    Icing resulting from an encounter with freezing precipitation, that 
is, supercooled drops with diameters exceeding 50 microns (defined as 
SLD, which includes both freezing drizzle and freezing rain). The 
Precipitation may be either within or outside of (usually below) the 
visible cloud.

Icing in Cloud

    Icing occurring within cloud (visible moisture) and temperature 
below freezing, but without precipitation visible. Cloud droplets 
(diameters 50 microns) will be present. SLD may or may not be present.

Supercooled Large Drops (SLD)

    SLD includes freezing rain or freezing drizzle.

Supercooled Drizzle Drops (SCDD)

    Are synonymous with freezing drizzle aloft.

Appendix C Icing Conditions

    Conditions for ice protection certification found in Appendix C of 
CFR 14 part 25.

L. Nicholas Lacey,
Director of Flight Standards.
[FR Doc. 00-32526 Filed 12-21-00; 8:45 am]
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