00-32526. Definition of Terms Applicable to In-Flight Icing Events

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of intent.

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: [phone].

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”.

(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]

The rate of ice accumulation may require occasional use of ice protection systems to remove/prevent accumulation.

Moderate ^[2]

The rate of ice accumulation is such that frequent use of ice protection systems is necessary.

Severe ^[3]

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.)

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.

Footnotes

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).

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).

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.