8900.1 CHG 425


Indicates new/changed information.

CHAPTER 27  Ground Deicing/Anti-Icing Programs

Section 5 Liquid Water Equivalent Systems

3-2249    GENERAL. A Liquid Water Equivalent System (LWES) is an automated precipitation measurement device that objectively measures the mass of frozen or freezing precipitation occurring over time and determines the Liquid Water Equivalent (LWE) rate in these conditions. An LWES may be a Holdover Time (HOT) Determination Systems (HOTDS) or Check Time (CT) Determination Systems (CTDS). The LWES does not rely upon visibility to estimate precipitation rate. The LWE rate is an accurate means for determining the anti-ice fluid endurance time (ET) based upon regression equations and regression coefficients specified in a Federal Aviation Administration (FAA)-approved current database (refer to The result of the automated process is either a HOT or CT for an aircraft’s applied anti-icing fluid (Society of Automotive Engineers (SAE) Types I, II, III, and IV). The HOTDS determines how long a fluid would provide protection assuming that the current conditions do not change. In contrast, the CTDS determines the fluid’s current protection capability while incorporating varying weather conditions.

3-2250    SCOPE. The information contained in this section applies to principal operations inspectors (POI) with oversight responsibility of certificate holders who conduct operations in accordance with Title 14 of the Code of Federal Regulations (14 CFR) parts 121, 125, and 135.

3-2251    ADDITIONAL GUIDANCE. The current edition of Advisory Circular (AC) 120-112, Use of Liquid Water Equivalent System to Determine Holdover Times or Check Times for Anti-Icing Fluids, contains information regarding LWESs.

3-2252    USING AN LWES TO SATISFY THE REGULATORY REQUIREMENTS FOR HOT. The FAA may authorize a certificate holder to use an LWES to provide HOT or CT information, depending on the regulatory part and the area in which a flight is being conducted. A POI, with the concurrence of the Air Transportation Division (AFS-200), grants authorization to use an LWES to a single, specific certificate holder. The FAA does not grant blanket authorizations of LWESs to a group of certificate holders.


A.    LWES for Parts 125 and 135. Part 125 or 135 certificate holders may choose to comply with part 121, 121.629(c) or part 135, 135.227(b)(2) or (3) by having an approved ground deicing/anti-icing program. POIs, with the concurrence of AFS-200, may grant part 125 and 135 certificate holders approval to use an LWES to provide HOT or CT reports to satisfy the requirements of the above regulations.

B.    LWES for Certificate Holders Conducting Part 121 Domestic, Flag, and Supplemental Operations. POIs of certificate holders who conduct part 121 domestic, flag, or supplemental operations may authorize the use of an LWES to provide HOT or CT reports to satisfy the ground deice/anti-ice program requirements of 121.629(c).


A.    Basic Requirements. The vendor should provide LWES documentation to the certificate holder showing the vendor’s program is consistent with AC 120-112. This documentation should include:

    Performance test report.

    Quality assurance (QA) documentation.

    System description.

    Verification report of HOT and/or CT determination.

    User’s manual and training material.

    Technician’s training manual.

    Maintenance manual.

    Siting and installation report.

    Maintenance log.

    System change proposal.

    Vendor letter stating the program is consistent with AC 120-112.

NOTE:  The certificate holder is responsible for ensuring that the LWES has an adequate level of accuracy and reliability to satisfy the 121.629(c) or 135.227(b)(2) or (3) regulatory requirements. The certificate holder must provide a letter to the POI stating that the certificate holder verifies that the LWES is consistent with AC 120-112 and will satisfy the applicable regulatory requirement listed above. Additionally, the certificate holder must provide the POI with any LWES documentation demonstrating consistency with AC 120-112 upon request. The certificate holder must notify the POI of any system revisions and provide system revision documentation to the POI upon request.

B.    Means of Communication to Flightcrew. Each certificate holder must describe its communications and data processing method (e.g., Aircraft Communications Addressing and Reporting System (ACARS)) to ensure this method is compatible with the vendor’s. Vendors currently use ACARS to transmit and/or communicate the information provided by the LWES to the certificate holder’s appropriate recipient(s), such as flightcrew members, dispatchers, and persons authorized to exercise operational control, but this method may change.

C.    Documentation and Record Retention. Part 121 certificate holders must have procedures in place to retain all LWES data in accordance with 121.711. This includes weather report parameters and data transmitted to the aircraft.

D.    Airplane Flight Manual (AFM)/AFM Supplement (AFMS)/Pilot’s Operating Handbook (POH) Content. The certificate holder must submit AFM/AFMS/POH LWES content describing the LWES system, listing the LWES authorized airport(s) and flightcrew member procedures for using LWES and reverting to the paper HOT when necessary. Additionally, the AFM/AFMS/POH must have a statement that the LWES may be used only for snow conditions.

E.    Training Requirements.

1)    Flightcrew members, deicing crews, dispatchers, and other affected personnel of the certificate holder must receive training on how to safely use the LWES. This training should follow the certificate holder’s current format/terms and must include but not be limited to:

    An overview of how LWES works and procedures for flightcrew members’ use of the LWES system, including system limitations.

    A list of procedures for flightcrew members to manage post-deicing changes in precipitation intensity.

    An explanation about how failures will be addressed (e.g., what happens when the system provides noncredible information or no information).

    In alignment with company policy, a review of the ability of the flightcrew to use an LWES as an additional decision support tool and reinforce that the pilot in command (PIC) retains final authority and responsibility for safe operation.

    Dissemination of HOT/CT information to crews (e.g., ACARS, what backups will be available, and procedures to follow).

    A reminder that the crew must maintain situational awareness. Pre-takeoff check (PTOC) is still required. The crew must obtain a new HOT/CT report or monitor (e.g., 5 minutes prior to takeoff or when precipitation intensity increases).

2)    When the LWES limit time is reached:

    If in active precipitation, the user is prohibited from departing without first conducting the pre‑takeoff contamination check in accordance with 121.629(c)(4) and the certificate holder’s deicing/anti-icing program.

    If precipitation ends prior to reaching the LWES limit time, the user may depart after successful PTOC.


A.    Operations Specification (OpSpec) Authorization. In order to authorize a certificate holder to use an LWES, POIs must enter the appropriate provider and airport information in the LWES tables provided in OpSpec A323, Liquid Water Equivalent System (LWES).

B.    Continued Regulatory Compliance. The certificate holder uses an LWES as a means to comply with certain weather requirements of parts 121, 125, and 135. However, simply having an LWES does not automatically satisfy the regulatory requirement to ensure the aircraft is free of frozen or freezing precipitation on departure. This means that each certificate holder, PIC, dispatcher, or person authorized to exercise operational control, as applicable, must consider all available information pertaining to weather conditions when making the decision on whether or not the aircraft is safe to depart. Should weather information or the LWES report be in conflict with the information prepared by another authorized or approved source (e.g., the Automated Weather Observing System (AWOS) or the Aviation Routine Weather Report (METAR)), each certificate holder, PIC, dispatcher, or person authorized to exercise operational control, as applicable, must be able to show that the LWES information is reliable or resort to using paper tables.


A.    Requests for Approval. POIs of certificate holders applying for authorization to use an LWES will direct the applicant to make a written request in accordance with Volume 3, Chapter 1, Section 1, and the LWES checklist. The request must describe the proposed LWES in sufficient detail to allow the POI to evaluate the proposal. The certificate holder must submit the following documentation to their POI.

1)    Operator letter requesting nonstandard LWES OpSpec A323 or OpSpec A341 authorization and operator letter stating the vendor’s program is consistent with AC 120-112.
2)    AFM, AFMS, or POH LWES content:

    LWES system description.

    LWES use for snow and/or freezing rain/freezing drizzle only statement.

    LWES cockpit procedures, including reversion to paper HOT.

    Airport(s) authorized.

3)    Content of pilot/dispatcher/deice crew procedures:

    LWES normal procedures.

    Dispatch considerations. Dispatchers will be trained on HOT or CT procedures and have full access to all HOT or CT crew documents.

4)    Phraseology.
5)    Non-normal procedures/reversion to paper HOT.
6)    LWES limitations.

    Use for snow and freezing rain/freezing drizzle.

    Other frozen precipitation/mixed precipitation not authorized.

7)    Airport(s) where authorized for use.
8)    Captain’s authority.
9)    Method of pilot/dispatcher/deice crew procedures training (e.g., 14 CFR part 142 training center, course of instruction, or in-house training).
10)    Record of course completion.

NOTE:  Operators should save records documenting completion in accordance with Volume 3, Chapter 31, Section 3.

B.    Review and Evaluate the Proposed LWES. Before approving a certificate holder’s LWES, POIs must review and evaluate the certificate holder’s proposal and any accompanying supporting documentation.

1)    Revision to an LWES. Any revisions to a certificate holder’s use of LWESs are subject to authorization for use by the POI.
2)    Denial of a Proposed LWES. If, after review and evaluation, the POI determines that a proposed LWES does not meet the requirements of 14 CFR and this section, or that he or she is otherwise unsatisfied with the LWES, the POI will return all submitted materials to the certificate holder, along with a letter outlining the deficiencies of the proposed LWES.
3)    Lack of Continued Adequacy of an LWES. If at any time a POI determines that an LWES does not continue to meet the requirements of 14 CFR and this section, or the POI determines the LWES is deficient in any way, the POI will immediately inform the certificate holder. If the certificate holder does not take immediate and appropriate corrective action, the POI must take action to amend the certificate holder’s OpSpec A041, Pretakeoff Contamination Check or Approved Alternate Ground Deicing/Anti-Icing Procedure for Title 14 CFR Part 125/135 Airplane Operations, in accordance with 121.629(c), and rescind authorization for use of the certificate holder’s LWES.

RESERVED. Paragraphs 3-2257 through 3-2260.