+-------------+------------------+-----------+-----+------------------+
| ![](me      |                  |           | *   |                  |
| dia/image1. |                  |           | *Ad |                  |
| wmf){width= |                  |           | vis |                  |
| "0.37708333 |                  |           | ory |                  |
| 33333333in" |                  |           | C   |                  |
| height="    |                  |           | irc |                  |
| 0.376388888 |                  |           | ula |                  |
| 8888889in"} |                  |           | r** |                  |
+-------------+------------------+-----------+-----+------------------+
| **U.S.      |                  |           |     |                  |
| D           |                  |           |     |                  |
| epartment** |                  |           |     |                  |
|             |                  |           |     |                  |
| **Of        |                  |           |     |                  |
| Trans       |                  |           |     |                  |
| portation** |                  |           |     |                  |
|             |                  |           |     |                  |
| Federal     |                  |           |     |                  |
| Aviation    |                  |           |     |                  |
|             |                  |           |     |                  |
| Adm         |                  |           |     |                  |
| inistration |                  |           |     |                  |
+-------------+------------------+-----------+-----+------------------+
| *           |                  | **Date:** |     | **AC No:**       |
| *Subject:** |                  | 12/09/08  |     | 150/5200-30C     |
| Airport     |                  |           |     |                  |
| Winter      |                  | **        |     | **Change:**      |
| Safety and  |                  | Initiated |     |                  |
| Operations  |                  | by:**     |     |                  |
|             |                  | AAS-100   |     |                  |
+-------------+------------------+-----------+-----+------------------+

1.  []{#__RefHeading___Toc213137103 .anchor}**PURPOSE.** This advisory
    circular (AC) provides guidance to assist airport operators in
    developing a snow and ice control plan, conducting and reporting
    runway friction surveys, and establishing snow removal and control
    procedures.

2.  []{#__RefHeading___Toc213137104 .anchor}**CANCELLATION.** This AC
    cancels AC 150/5200-30B, *Airport Winter Safety and Operations,*
    dated September 5, 2007

3.  []{#OLE_LINK2 .anchor}**APPLICATION.** This AC contains guidance on
    developing plans, methods, and procedures for snow and ice control
    equipment, materials, and removal that are acceptable to the
    Administrator and in accordance with Title 14, Code of Federal
    Regulations (CFR), Part 139, Certification of Airports, Section
    139.313, Snow and Ice Control. Certificated airports are required to
    follow the requirements of paragraphs 5-6 and 5-7 as of the
    effective date of this AC. In addition, all certificated airports
    must submit revised Snow and Ice Control Plans to the FAA no later
    than April 30, 2009 for approval. At that time, certificated
    airports will be required to comply with the remaining portions of
    this AC. The AC is advisory for non-certificated airports.

4.  **PRINCIPAL CHANGES.** The AC incorporates the following principal
    changes:

    a.  Paragraph 1-3 clarifies that the location of the snow control
        center may range from a separate room/facility to a specially
        equipped operations vehicle.

    b.  Paragraph 5-6 establishes the winter related conditions that
        initiate a requirement for closing a runway.

    c.  Various new or revised text changes that relate to paragraph 5-6
        requirements.

5.  []{#__RefHeading___Toc213137107 .anchor}**METRIC UNITS.** This AC
    contains both English and metric dimensions. The metric conversions
    may not be exact, so the English system governs.

![](media/image2.jpeg){width="1.9972222222222222in"
height="0.7979166666666667in"}

Michael J. O'Donnell

Director of Airport Safety and Standards

Page intentionally blank

**Table of Contents**

# 

**1. PURPOSE [i](#__RefHeading___Toc213137103)**

2\. CANCELLATION. [i](#__RefHeading___Toc213137104)

3\. APPLICATION [i](#OLE_LINK2)

4\. PRINCIPAL CHANGES. [i](#OLE_LINK2)

5\. METRIC UNITS. [i](#__RefHeading___Toc213137107)

Tables [v](#tables)

Chapter 1. Introduction [1](#chapter-1.-introduction)

1-1. Snow and Ice Control Committee. [1](#_Ref214935919)

1-2. Airport Snow and Ice Control Committee (SICC).
[1](#__RefHeading___Toc213137111)

1-3. Snow Control Center (SCC). [1](#__RefHeading___Toc213137112)

1-4. Airfield Clearing Priorities for the Snow and Ice Control Plan
(SICP [2](#onefour)

1-5. Terminal and Landside -- Ground Side Priority. [3](#_Ref213141880)

1-6. Airfield Clearance Times. [3](#__RefHeading___Toc213137115)

1-7. Sizing and Staffing Snow and Ice Control Equipment Fleet.
[4](#__RefHeading___Toc213137116)

1-8. Storage of Snow and Ice Control Equipment.
[4](#__RefHeading___Toc213137117)

1-9. Definitions. [5](#__RefHeading___Toc213137118)

Chapter 2. The Snow and Ice Control Plan
[7](#chapter-2.-the-snow-and-ice-control-plan)

2-1. Safety Requirements. [7](#__RefHeading___Toc213137120)

2-2. Topics for Pre- and Post-Season SICC Meetings.
[8](#__RefHeading___Toc213137121)

2-3. Outlining a Snow and Ice Control Plan (SICP).
[10](#__RefHeading___Toc213137122)

2-4. Topics for Writing Instructions and Procedures for Winter
Operations and Notification. [11](#__RefHeading___Toc213137123)

2-5. Runway Incursion Mitigation and Operations During Non-Towered Air
Traffic Control Periods. [11](#__RefHeading___Toc213137124)

2-6. Staff Training and Recordkeeping.
[12](#__RefHeading___Toc213137125)

2-7. Other Related Items. [13](#__RefHeading___Toc213137126)

Chapter 3. Snow Clearing Operations and Preventive Measures
[15](#chapter-3.-snow-clearing-operations-and-preventive-measures)

3-1. Weather Forecasting. [15](#__RefHeading___Toc213137128)

3-2. FAA Forecasting Research and Development for Airport Operators.
[15](#__RefHeading___Toc213137129)

3-3. Forecasting Runway Surface Conditions
[18](#__RefHeading___Toc213137130)

Chapter 4. Snow Clearing Operations and Ice Prevention
[19](#chapter-4.-snow-clearing-operations-and-ice-prevention)

4-1. Introduction. [19](#_Ref213137814)

4-2. Snow Clearing Principles [19](#fourtwo)

4-3. Controlling Snow Drifts. [28](#__RefHeading___Toc213137134)

4-4. Snow Disposal. [29](#__RefHeading___Toc213137135)

4-5. Methods for Ice Control and Removal.
[29](#__RefHeading___Toc213137136)

4-6. Approved Chemicals [30](#__RefHeading___Toc213137137)

4-7. Runway Friction Improvements. [32](#__RefHeading___Toc213137138)

4-8. Sand. [34](#__RefHeading___Toc213137139)

Sieve Designation [35](#sieve-designation)

Percent by Weight Passing [35](#percent-by-weight-passing)

Chapter 5. Runway Surface Assessment and Reporting
[37](#chapter-5.-runway-surface-assessment-and-reporting)

5-1. Introduction. [37](#fiveone)

5-2. Runway Condition Reporting. [38](#__RefHeading___Toc213137144)

5-3. Runway Friction Surveys. [39](#__RefHeading___Toc213137145)

5-4. FAA-Approved Runway Friction Measuring Equipment.
[40](#__RefHeading___Toc213137146)

5-5. Friction Assessment Reporting. [43](#fivefour)

5-6. Requirements For Runway Closures.
[44](#__RefHeading___Toc213137148)

5-7. Continuous Monitoring. [45](#__RefHeading___Toc213137149)

APPENDIX 1. Development of Recommended Snow Bank Height Profiles
[47](#section-3)

APPENDIX 2. Snow and Ice Control as a Materials-Handling Problem
[51](#appendix-2.-snow-and-ice-control-as-a-materials-handling-problem)

A2-1. Introduction. [51](#__RefHeading___Toc213137152)

A2-2. Snow. [51](#__RefHeading___Toc213137153)

A2-3. Ice. [52](#__RefHeading___Toc213137154)

A2-4. Slush. [54](#__RefHeading___Toc213137155)

APPENDIX 3. FAA-Approved Decelerometers\*
[55](#appendix-3.-faa-approved-decelerometers)

A4-1. Scope. [57](#__RefHeading___Toc213137157)

A4-2. Certification (General). [57](#__RefHeading___Toc213137158)

A4-3. Certification (Electronic Only).
[58](#__RefHeading___Toc213137159)

A4-4. Decelerometer Calibration. [58](#__RefHeading___Toc213137160)

A4-5. Training. [59](#__RefHeading___Toc213137161)

# 

**Figures**

[Figure 1-1. Example of Prioritized Paved Areas for the Snow and Ice
Control Plan 2](#__RefHeading___Toc212272465)

[Figure 3-1. Single Alter Wind Shield Type
16](#__RefHeading___Toc212272466)

[Figure 3-2. Schematic of Unidirectional Storm WSDDM Configuration
17](#__RefHeading___Toc212272467)

[Figure 4-1. Snow Bank Profile Limits Along Edges of Runways and
Taxiways with the Airplane Wheels on Full Strength Pavement (see Figure
4-2 guidance) 24](#__RefHeading___Toc212272468)

[Figure 4-2. ILS CAT I and CAT II/III Snow Clearance Area Depth
Limitations 25](#__RefHeading___Toc212272469)

[Figure 4-3. Possible Team Configuration with Perpendicular Wind
26](#__RefHeading___Toc212272470)

[Figure 4-4. Possible Team Configuration During Light Snowfall with
Parallel or Calm Wind 26](#__RefHeading___Toc212272471)

[Figure 4-5. Possible Team Configuration During Medium to Heavy Snowfall
with Parallel or Calm Wind (Dependent upon Rotary Plow performance)
27](#__RefHeading___Toc212272472)

[Figure 4-6. Typical Snow Trench Dimensions
29](#__RefHeading___Toc212272473)

[Graph A1-1. Individual height profiles of airplane wingtips and outer
and inner engine nacelles' lower edges for Airplane Design Groups III
and IV 48](#__RefHeading___Toc212272474)

[Graph A1-2. Individual height profiles of airplane wingtips and outer
and inner engine nacelles' lower edges for Airplane Design Groups V and
VI (\* indicates preliminary data) 49](#__RefHeading___Toc212272475)

# Tables

# 

[Table 1-1. Clearance Times for Commercial Service Airports
3](#__RefHeading___Toc212274678)

[Table 1-2. Clearance Times for Non-Commercial Service Airports
4](#__RefHeading___Toc212274679)

[Table 4-1. Guidance for Airside Urea Application Rates
31](#__RefHeading___Toc212274680)

[Table 4-2. Standard Gradation for Sand
34](#__RefHeading___Toc212274681)

[Table 4-3. Expanded Sand Gradation Standard
35](#__RefHeading___Toc212274682)

[Table 5-1. Runway Contamination Mitigation Record and Runway Friction
Survey Record 46](#__RefHeading___Toc212274684)

Page intentionally blank

# Chapter 1. Introduction

1.  []{#_Ref214935919 .anchor}**Snow and Ice Control Committee.** The
    presence of contaminants such as snow, ice, or slush on airfield
    pavements and drifting snow causes hazardous conditions that may
    contribute to airplane incidents and accidents. Further, winter
    storm conditions usually reduce airport traffic volumes through
    flight delays and/or cancellations and, in severe storm conditions,
    airport closures. The extent to which these undesirable effects are
    minimized will depend on the approach taken by the airport operator
    to combat winter conditions. The most successful airport operators
    at combating winter storms are those that establish an airport snow
    and ice control committee that conducts pre- and post-seasonal
    planning meetings, operates a snow control center (SCC), and, most
    importantly, implements a written plan. This advisory circular
    provides recommendations and guidance for writing plans plus
    identifies topics that should receive special focus to improve
    operational safety. For airports certificated under 14 CFR Part 139,
    *Certification of Airports* (Part 139)*,* the written plan is
    referred to as the *Snow and Ice Control Plan* (see section 139.313,
    *Snow and Ice Control.)*

2.  []{#__RefHeading___Toc213137111 .anchor}**Airport Snow and Ice
    Control Committee (SICC).** All airports subject to icing conditions
    or annual snowfall of several inches (6 inches (15 cm) or more)
    should have a SICC. Such committees have been effective in (1)
    preseason planning, (2) focusing the operational plan to improve
    runway safety and communications between various offices/departments
    involved or impacted by a storm event, (3) addressing the needs of
    airport users, and (4) critiquing clearing activities of the
    airfield and ramp areas after the winter season and after each storm
    event. It is recommended that ongoing evaluation meetings be held,
    preferably after each storm event, to allow evaluation of
    procedures, identify safety concerns, and, when necessary, implement
    revised clearing procedures. The SICC size and functions will vary
    based on the airport size, airport users, and the type of winter
    weather experienced within its geographical location. The airport
    manager or his/her representative should chair the SICC. The
    committee should include representatives from the following:

    -   Airport operations staff.

    -   Airline flight operations departments or fixed-base operators
        and airline station personnel (deicing representatives).

    -   FAA air traffic control, flight station, technical operations.

    -   Other concerned parties deemed necessary, such as the U.S.
        military (at joint-use airports), service providers, and
        contractors who may be actively conducting construction
        activities.

3.  []{#__RefHeading___Toc213137112 .anchor}**Snow Control Center
    (SCC).** The airport operator should set up a *Snow Control Center
    (SCC)* for snow and ice control activities. Depending on the size of
    the airport and its operations, the SCC may be in a special room or
    facility, or it might be a "snow desk" in a maintenance building, or
    it could be the command vehicle of the operations officer. The SCC
    performs the following main functions: (1) managing snow clearing
    operations; (2) serving as a prime source of field condition
    reporting, e.g., timely runway braking conditions, snow
    accumulations, etc.; (3) informing the airport traffic control tower
    (ATCT), air carriers, air taxis, and other parties of expected
    runway closures and openings; and (4) issuing timely NOTAMs (see AC
    150/5200-28, *Notices to Airmen (NOTAMs) for Airport Operators,* and
    FAA Orders 7930.2, *Notices to Airmen (NOTAMS),* and 7340.1,
    *Contractions.*

[]{#onefour .anchor}

4.  **Airfield Clearing Priorities for the Snow and Ice Control Plan
    (SICP).** Airport operators cannot simultaneously clear all snow,
    slush, ice, or drifting snow from both the entire aircraft movement
    area and all supporting facilities necessary for flight. However,
    the airport operator can limit interruption of service as much as
    possible by classifying the most critical portions of the aircraft
    movement area and supporting facilities as Priority 1 and then
    taking care of other areas in their order of importance. For such a
    system to work, the SICP should identify at a minimum two priority
    categories based on the airport's safety requirements, flight
    operations, visual navigation aids (VISAIDs) and electronic
    navigational aids (NAVAIDs), and other factors deemed important by
    the airport operator. Figure 1-1 illustrates an airport with
    typically prioritized areas.

    a.  **Priority 1.** Items normally included in this category are the
        primary runway(s) with taxiway turnoffs, access taxiways leading
        to the terminal, terminal(s) and cargo ramp(s), airport rescue
        and fire fighting (ARFF) station(s) and emergency service roads,
        NAVAIDs, and other areas deemed essential, such as fueling areas
        and airport security/surveillance roads.

    b.  **Priority 2.** Items normally included in this category are
        crosswind/secondary runways and their supportive taxiways,
        remaining aircraft movement areas, commercial ramp areas, access
        roads to secondary facilities, and airfield facilities not
        essential to flight operations or not used on a daily basis.

![](media/image3.wmf){width="3.5972222222222223in"
height="3.529861111111111in"}

Figure 1-. Example of Prioritized Paved Areas for the Snow and Ice
Control Plan

5.  []{#_Ref213141880 .anchor}**Terminal and Landside -- Ground Side
    Priority.** The clearing of snow from the terminal and landside
    infrastructure to and from the terminal is a separate category
    generally not contained in the SICP because the objective of this
    clearing operation is public access, not airplane operational
    safety. Moreover, different chemicals, clearing equipment, and
    techniques, and possibly the use of municipal or service
    contractors, might be standard for such operations

6.  []{#__RefHeading___Toc213137115 .anchor}**Airfield Clearance
    Times.** Airports should have sufficient equipment to clear within a
    reasonable time 1 inch (2.54 cm) of snow weighing up to 25 lb/ft^3^
    (400 kg/m^3^) for the priorities outlined in Paragraph 1-4 that
    accommodate anticipated airplane operations. If supportive runways
    (such as a parallel runway) typically have simultaneous operations
    during the winter months, then the areas for both runways and
    associated principal taxiways should be included in the total area.
    The term "reasonable time," as used in this AC, is based on the
    airport type and number of annual operations. The guidance in a.
    and b. below is provided to assist the airport operator in
    determining necessary equipment. It should not be interpreted as a
    requirement to clear surfaces within any particular time.

    a.  First, use the footnote in Table 1-1 to classify the airport as
        a *Commercial Service Airport* or a *Non-Commercial Service
        Airport*.

[]{#__RefHeading___Toc212274678 .anchor}Table 1-1. Clearance Times for
Commercial Service Airports

+------------------------------------+---------------------------------+
| ***Annual Airplane Operations***   | ***Clearance Time^1^***         |
|                                    |                                 |
| (includes cargo operations)        | ***(hour)***                    |
+------------------------------------+---------------------------------+
| *40,000 or more*                   | *½*                             |
+------------------------------------+---------------------------------+
| *10,000 -- but less than 40,000*   | *1*                             |
+------------------------------------+---------------------------------+
| *6,000 -- but less than 10,000*    | *1½*                            |
+------------------------------------+---------------------------------+
| *Less than 6,000*                  | *2*                             |
+------------------------------------+---------------------------------+
| *General: Commercial Service       |                                 |
| Airport means a public-use airport |                                 |
| that the U.S. Secretary of         |                                 |
| Transportation determines has at   |                                 |
| least 2,500 passenger boardings    |                                 |
| each year and that receives        |                                 |
| scheduled passenger airplane       |                                 |
| service \[reference Title 49       |                                 |
| United States Code, Section        |                                 |
| 47102(7)\].*                       |                                 |
|                                    |                                 |
| *Footnote 1: These airports should |                                 |
| have sufficient equipment to clear |                                 |
| 1 inch (2.54 cm) of falling snow   |                                 |
| weighing up to 25 lb/ft^3^ (400    |                                 |
| kg/m^3^) from Priority 1 areas     |                                 |
| within the recommended clearance   |                                 |
| times.*                            |                                 |
+------------------------------------+---------------------------------+

[]{#__RefHeading___Toc212274679 .anchor}Table 1-2. Clearance Times for
Non-Commercial Service Airports

+------------------------------------+---------------------------------+
| ***Annual Airplane Operations***   | ***Clearance Time^1^***         |
|                                    |                                 |
| (includes cargo operations)        | ***(hour)***                    |
+------------------------------------+---------------------------------+
| *40,000 or more*                   | *2*                             |
+------------------------------------+---------------------------------+
| *10,000 -- but less than 40,000*   | *3*                             |
+------------------------------------+---------------------------------+
| *6,000 -- but less than 10,000*    | *4*                             |
+------------------------------------+---------------------------------+
| *Less than 6,000*                  | *6*                             |
+------------------------------------+---------------------------------+
| *General: Although not             |                                 |
| specifically defined,              |                                 |
| Non-Commercial Service Airports    |                                 |
| are airports that are not          |                                 |
| classified as Commercial Service   |                                 |
| Airports \[see Table 1-1,general   |                                 |
| note\].*                           |                                 |
|                                    |                                 |
| *Footnote 1: These airports may    |                                 |
| wish to have sufficient equipment  |                                 |
| to clear 1 inch (2.54 cm) of       |                                 |
| falling snow weighing up to 25     |                                 |
| lb/ft^3^ (400 kg/m^3^) from        |                                 |
| Priority 1 areas within the        |                                 |
| recommended clearance times.*      |                                 |
+------------------------------------+---------------------------------+

b.  Second, using the appropriate table, find the number of annual
    airplane operations handled by the airport and the recommended
    clearance time. As shown, this action-initiating condition, compared
    with an action-initiating event based on weather forecasts or runway
    surface condition sensors, calls for clearing operations for 1-inch
    (2.54-cm) snowfall with an assumed weight (snow density) of up to 25
    lb/ft^3^ (400 kg/m^3^). For airports located in regions where snow
    densities over 25 lb/ft^3^ (400 kg/m^3^) are the norm, the airport
    operator should consider using a *½-*inch (1.25 cm) snow depth as
    the action-initiating condition. Airport operators should keep in
    mind that heavier snow densities can increase the size and type of
    equipment comprising the fleet used to clear Priority 1 paved areas
    within the recommended clearance times (for details, see AC
    150/5220-20, *Airport Snow and Ice Control Equipment*.)

```{=html}
<!-- -->
```
7.  []{#__RefHeading___Toc213137116 .anchor}**Sizing and Staffing Snow
    and Ice Control Equipment Fleet.** Sizing the snow and ice control
    equipment fleet should be based on the total Priority 1 paved area
    that is cleared of snow, slush, or ice within a recommended
    clearance time. AC 150/5220-20 offers guidance on how to select the
    number and types of equipment necessary to meet recommended
    clearance times. As for staffing, Part 139, sections 139.303(a)
    and (b) relate equipment fleet size with sufficient, qualified
    staff. Section 139.303(b) requires certificate holders "*to equip
    personnel with sufficient resources needed to comply with the
    requirements of this part*." Part 139, section 139.303(a) requires
    certificate holders "*to provide sufficient and qualified personnel
    to comply with the airport's Airport Certification Manual and the
    requirements of this part*." While snow removal and surface
    treatment may be adequate for runways, the adequacy should extend to
    keeping all required associated taxiways cleared and to maintaining
    adequate surface friction to the extent practical.

8.  []{#__RefHeading___Toc213137117 .anchor}**Storage of Snow and Ice
    Control Equipment.** Whenever possible, snow and ice control
    equipment should be housed in a heated building to prolong the
    useful life of the equipment and to enable more rapid response to
    operational needs. Additionally, repair facilities should be
    available within the building for onsite equipment maintenance and
    repair during the winter season. Operationally, equipment should be
    inspected after each use to determine whether additional maintenance
    or repair is necessary. Guidance on storing snow and ice control
    equipment is provided in AC 150/5220-18, *Buildings for Storage and
    Maintenance of Airport Snow and Ice Control Equipment and
    Materials.*

9.  []{#__RefHeading___Toc213137118 .anchor}**Definitions.**

    a.  **Contaminant.** Any substance on a runway. For the purposes of
        this AC, references to contaminants mean winter contaminants
        such as snow, slush, ice or standing water.

    b.  **Eutectic Temperature/Composition.** A deicing chemical melts
        ice by lowering the freezing point. The extent of this freezing
        point depression depends on the chemical and water in the
        system. The limit of freezing point depression, equivalent to
        the lowest temperature that the chemical will melt ice, occurs
        with a specific amount of chemical. This temperature is called
        the eutectic temperature, and the amount of chemical is the
        eutectic composition. Collectively, they are referred to as the
        eutectic point**.**

    c.  **Ice.** The solid form of water consisting of a characteristic
        hexagonal symmetry of water molecules. The density of pure ice
        is 57 lb/ft^3^ (913 kg/m^3^), which is 9 percent less dense than
        water. Compacted snow becomes ice when the air passages become
        discontinuous at a density of about 50 lb/ft^3^ (800 kg/m^3^).

    d.  **Snow (on the ground).** A porous, permeable aggregate of ice
        grains, which can be predominately single crystals or close
        groupings of several crystals.

        1.  **Dry Snow.** Snow that has insufficient free water to cause
            cohesion between individual particles. This generally occurs
            at temperatures well below 32° F (0° C). If when making a
            snowball, it falls apart, the snow is considered dry.

        2.  **Wet Snow.** Snow that has grains coated with liquid water,
            which bonds the mass together, but that has no excess water
            in the pore spaces. A well-compacted, solid snowball can be
            made, but water will not squeeze out.

        3.  **Compacted Snow.** Snow that has been compressed into a
            solid mass that resists further compression and will hold
            together or break up into lumps if picked up.

    e.  **Slush.** Snow that has water content exceeding its freely
        drained condition such that it takes on fluid properties (e.g.,
        flowing and splashing). Water will drain from slush when a
        handful is picked up. This type of water-saturated snow will be
        displaced with a splatter by a heel and toe slap-down motion
        against the ground.

    f.  **Patchy Conditions.** Areas of bare pavement showing through
        snow and/or ice covered pavements. Patches normally show up
        first along the centerline in the central portion of the runway
        in the touchdown areas.

    g.  **Primary Runway.** A runway expected to be used under the
        existing atmospheric and storm event conditions where most of
        the takeoff and landing operations will take place.

    h.  **Secondary Runway.** A runway that supports a primary runway.
        Takeoff and landing operations on such a runway are generally
        less frequent than on a primary runway.

# Chapter 2. The Snow and Ice Control Plan

1.  []{#__RefHeading___Toc213137120 .anchor}**Safety Requirements.**
    Snow, ice, and slush should be removed as expeditiously as possible.
    The goal is to maintain runways, high-speed turnoffs, and taxiways
    in a *"no worse than wet"* (i.e., no contaminant accumulation)
    condition, realizing that this is not always possible. Surface
    friction can be improved by application of sand when unusual
    conditions prevent prompt and complete removal of slush, snow, or
    ice. Operations of snow removal equipment and support vehicles must
    be conducted to prevent runway incursions and interference or
    conflict with airplane operations. This safety responsibility is
    shared by airport personnel, airplane operators, and any contract
    service providers. The reduced hours of daylight during the winter
    and frequent low-visibility conditions resulting from fog, blowing
    snow, or precipitation require extra care during field operations
    and greater attention to enhancing visibility of equipment
    performing winter maintenance (i.e., snow removal, friction
    enhancement, etc.). Post-clearing operations must be conducted to
    ensure airfield signage and markings between the runway(s) and apron
    are visible to pilots to reduce the potential for runway incursions.

    a.  **Airport Operators.** Airport operators have a major duty to
        ensure the safety of operations at their facilities. This
        involves performance according to accepted principles, ensuring
        a high standard of care, providing state-of-the-art standards in
        equipment and techniques, and maintaining qualified crews. Care
        should be taken to ensure the snow and ice control plan is
        current, complete, and customized to the local conditions. All
        airport leases and agreements should be clear and specific and
        cover the duties and responsibilities of lessees to carry out
        their assigned snow and ice control duties. Airport operators,
        however, have the duty to warn the users of the airport of any
        change in published procedure or change in the physical
        facility. As an example, an airport operator should give
        *timely* or *proper notice* of pavement or visual aids that may
        have been damaged by a snow plowing operation. Complete
        documentation of compliance with the snow and ice control plan
        (SICP) should be kept. This advisory circular will use the term
        "*Snow and Ice Control Plan*" to represent all types of snow and
        ice control plans.

    b.  **Snow and Ice Control Plans.** The Snow and Ice Control Plan
        (SICP) is a basic document encompassing at least two separate
        phases. Phase #1 addresses pre- and post-winter season subjects
        that prepare the airport operator for the new winter season.
        This phase may include revising the existing SICP after the
        winter season ends. Phase #2 addresses the sequential actions,
        via instruction and procedures, taken by the airport operator
        for dealing with winter storms and notifying airport users in a
        timely manner when less than satisfactory conditions exist at
        the airport including the closure of runways. Chapters 1, 3, 4,
        and 5 of this AC offer guidance, recommendations, and standards
        for writing instructions and procedures for Phase #2.
        Additionally, Sections 2 and 3 of this Chapter should be used to
        maintain a safer airfield. At minimum, the following questions
        should be addressed when outlining new plans or revising
        existing plans.

-   Are we materially prepared and adequately budgeted for the new
    winter season?

-   Did the SICP incorporate identified post-season improvements?

-   Are we staffed adequately with qualified personnel?

-   Is our training program adequately tracking test records and
    development of qualified personnel?

-   Do our environmental mitigation procedures for disposal of deicers
    and equipment maintenance materials and supplies keep us in
    compliance with storm water regulations?

-   Should our Snow and Ice Control Committee (SICC) conduct more pre-
    and post-season meetings?

-   Did our weather forecasting method monitor last year's storm events
    accurately and in a timely manner?

-   Do we need to change our prescribed storm conditions to start
    clearing operations or preventive measures?

-   Do we need to change our runway closure procedures as defined in
    paragraph 5-6 for closing a runway and other paved areas used by
    airplanes?

-   In reference to our runway closure procedure, do we need to revise
    the steps we prescribed in the SICP for continuously monitoring the
    runway(s)?

-   Do the same personnel continue to initiate the runway closure
    procedure (as developed by the airport) and are there any new
    procedures for the closure of a runway?

-   Are there any changes to our chain-of-command and phone numbers?

-   Do we need to update or issue a Letter of Agreement (LOA) with the
    airport traffic control tower (ATCT) or other parties for
    implementing runway closure procedures?

-   Were there any changes to the airfield areas to be cleared and
    maintained, the timing of operations, and how clearing will be done?

-   Are we informing our users frequently and in a timely manner when we
    must close the airport or report less than satisfactory surface
    conditions? Did we get complaints?

-   Are we meeting all applicable Part 139 requirements?

-   How do we ensure markings, signs, and lighting systems are
    legible/visible after clearing operations? Are touchdown markings
    addressed in our procedures?

-   What are our procedures in case of airfield accidents involving snow
    clearing crews, airplanes, or other airport vehicles?

-   Did we address all unique airport site conditions?

-   Have all storm crews received training on the SICP and trained on
    new equipment?

2.  []{#__RefHeading___Toc213137121 .anchor}**Topics for Pre- and
    Post-Season SICC Meetings.** As with all plans, the SICP should be
    reviewed at least annually to collectively assess the previous
    year's program. Three general topics are recommended for discussion,
    namely to incorporate (1) changes to airport staff, equipment,
    runway chemicals, and airport clearing procedures; (2) changes to
    air carrier ground deicing/anti-icing programs; and (3) *"lessons
    learned"* from actual events encountered. The FAA recommends that
    before each winter season, the SICC holds a series of meetings to
    prepare for and adequately budget for the upcoming winter season.
    Two distinct meetings should be held; one focused on airport
    clearing operations, and the other focused on air carrier ground
    deicing/anti-icing programs. Each meeting should discuss any new
    topics not dealt with in past years, such as new FAA aircraft ground
    deicing/anti-icing polices and new Federal, state, or local storm
    water runoff regulations.

    a.  **Topics Relative to Airport Clearing Operations Discussions.**
        The following are topics normally covered:

-   Areas designated as Priority 1 areas, to include any new airfield
    infrastructure.

-   Clearing operations and follow-up airfield assessments to further
    mitigate the potential for pilot and vehicular surface incidents or
    runway incursions.

-   Staffing requirements and qualifications (training) for snow crews
    and Snow Control Center staff.

-   Update to the training program to close any ambiguity.

-   Streamline decision-making process, the "line-of-command" authority.

-   Response times to keep runways, taxiways, and ramp areas
    operational, e.g., to rectify problems encountered during previous
    storm events that hampered airport operations.

-   Communications, terminology, frequencies, and procedures with the
    airport traffic control tower (ATCT), snow crews, and the Snow
    Control Center.

-   Monitoring and updating of runway surface conditions after a
    clearing operation and deicing or sanding applications.

-   Issuance of NOTAMs and dissemination to ensure timely notification.

-   Equipment inventory, including assessing the condition of snow
    control equipment, scheduling repairs, and stocking spare parts.

-   Status of procurement contracts and specifications for new vehicles
    or equipment.

-   Preventive maintenance program for snow control equipment and
    maintenance and calibration for friction testing equipment.

-   Status of procurement contracts and specifications for
    deicer-/anti-icer materials and sand supply, including their storage
    before the first snowfall.

-   Validation of deicer certification letters from vendors.

-   Procedures for storm water runoff mitigation.

-   Snow hauling and/or disposal plan, including sites for dumping snow.

-   New runoff requirements for the containment and/or collection of
    deicing chemicals and vehicle maintenance fluids and materials.

-   Changes to contract service for clearing ramps.

    a.  **Topics Relative to Air Carrier Ground Deicing/Anti-icing
        Programs.** The airport operator should act as a facilitator and
        arrange a meeting for the parties that may be affected by
        airplane ground deicing plans, including those plans required of
        air carriers operating under 14 CFR Part 121, *Operating
        Requirements: Domestic, Flag, and Supplemental Operations*.
        These parties include airport management and consultants, the
        air carriers, other airport users, corporate tenants, pilot
        representatives, and FAA Air Traffic Control. The meeting should
        assess the impact of any airplane ground deicing activities on
        airport operations and identify actions that can be taken by the
        various parties to maximize the efficiency of operations during
        icing conditions. For example, the committee may be able to
        identify the most effective locations for secondary deicing and
        establish procedures for its implementation. At most airports,
        one meeting to discuss these subjects before the start of the
        winter season should suffice. However, at other airports,
        subsequent meetings may be necessary to assess the effectiveness
        of plans and to modify them if necessary. These meetings
        typically address the following topics:

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-   Assessment of all air carriers' deicing programs from the previous
    year, including---

    -   Reviewing airplane surface flow strategies.

    -   Reviewing ground time and takeoff clearances after deicing.

    -   Analyzing and adjusting to airplane deicing plans.

-   Actions needed to maximize efficiency of operations during icing
    conditions, including---

    -   Identifying locations for airplane deicing that use chemicals or
        infrared deicing technology.

    -   Planning taxi routes to minimize ground time.

    -   Developing rates that control deiced departures.

    -   Allocating departure slot capacities.

    -   Determining airport deicing crew needs.

    -   Verifying communication procedures between air traffic control
        and airplanes to be deiced.

-   Any requirements for containment/collection of deicing/anti-icings.

3.  []{#__RefHeading___Toc213137122 .anchor}**Outlining a Snow and Ice
    Control Plan (SICP).**

    a.  A logical first step in writing the SICP is to identify and
        prioritize those aircraft movement areas to be cleared of snow
        and/or ice within certain times. Paragraphs 1-4 and 1-5 of this
        advisory circular discuss airfield clearing priorities and
        clearance times. These parameters, in turn, guide the airport
        operator in selecting the conditions that initiate activities,
        such as, clearing operations, chemical applications, runway
        friction surveys, and other operations. (Chapter 3 provides
        information about action-initiated conditions and events.)

Next, the SICP must include instructions and procedures for handling the
various types of winter storms encountered by the airport and how to
notify airport users in a timely manner of other than nominal runway
conditions, including, but not limited to: runway closures, and when any
portion of the movement area normally available to them is covered by
snow, slush, ice, or standing water.

b.  When winter contaminants are present on pavements and/or a runway
    has to be closed, Section 1 of this Chapter provides the minimal
    list of what is to be done, while Chapters 4 and 5 offer guidance,
    recommendations, and standards for writing the instructions and
    procedures.

c.  Finally, the SICP should address special safety topics to minimize
    runway incursions during initial and follow-up clearing operations.
    Sections 2 and 3 of this Chapter offer guidance and recommendations
    for this step.

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4.  []{#__RefHeading___Toc213137123 .anchor}**Topics for Writing
    Instructions and Procedures for Winter Operations and
    Notification.** Part 139 airports are required to address the
    following topics in their SICP, and it is recommended that all other
    airport operators address the same topics in their SICP. Each topic
    provides a cross-reference for further clarification.

    a.  Prompt removal or control, as completely as practical, of snow,
        ice, and slush on each movement area (see Paragraph 1-1 and
        Chapter 3).

    b.  Positioning snow off the movement area surfaces so all airplane
        propellers, engine pods, rotors, and wing tips will clear any
        snowdrift and snow bank as the airplane's landing gear traverses
        any portion of the movement area (see Chapter 4, Paragraph 4-1
        and Figure 4-1).

    c.  Selection and application of authorized materials for snow and
        ice control to ensure they adhere to snow and ice sufficiently
        to minimize engine ingestion (see Chapter 4, Paragraphs 4-6and
        4-7).

    d.  Timely commencement of snow and ice control operations (see
        Paragraph 1-1 and Chapter 3).

    e.  Prompt notification in accordance with Part 139.339, *Airport
        Condition Reporting*, to all air carriers using the airport when
        any portion of the movement area normally available to them is
        less than satisfactorily cleared for safe operation by their
        aircraft (see Chapter 5, Paragraphs 5-6, *Requirements for
        Runway Closures*, and 5-2, *Runway Condition Reporting*). In
        addition, all airplane operators should be informed any time
        pavements are contaminated with ice, snow, slush, or standing
        water.

5.  []{#__RefHeading___Toc213137124 .anchor}**Runway Incursion
    Mitigation and Operations During Non-Towered Air Traffic Control
    Periods.** The SICP should contain specific procedures for those
    periods when the ATCT is closed and for airports that do not have an
    ATCT (non-towered airport). Additionally the SICP should contain
    specific procedures for unexpected situations, such as when
    "whiteout" conditions occur while snow clearing crews occupy the
    runways. The following items should be considered:

    a.  Runway clearing procedures must ensure snow removal operations
        will not create the possibility for a runway incursion after the
        runway reopens, for example, by covering taxiway signs with
        plowed snow. The SICP should specifically address that taxiway
        directional signs, such as those leading out and toward the
        terminal area(s), and runway holding position signs are legible
        and light fixtures are distinguishable after clearing
        operations.

    b.  Although it is not required, airport operators should consider
        closing runways during snow clearing operations. For airport
        operators that choose to keep runways open during such
        operations, the SICP should include procedures requiring
        continuous coordination among the clearing crew and the SCC to
        ensure the equipment operators on runways are aware of their
        surroundings. Snow removal equipment operators should monitor
        appropriate air traffic control (ATC) or other frequencies for
        information on approaching or departing airplanes.

    c.  The overlying air traffic control frequency should be monitored
        along with the local frequency by the airport's Snow Control
        Center at all non-towered airports and at airports where the
        ATCT has less than 24-hour operations. This should apply even if
        a NOTAM has been issued closing the runway for snow clearing
        operations. Such monitoring is especially important during
        marginal visual meteorological condition (VMC) and instrument
        meteorological condition (IMC).

  -----------------------------------------------------------------------
  **Note:** The overlying air traffic facility may be enroute, terminal,
  or flight service. Monitoring is recommended for snow crews to hear an
  airplane approaching and therefore be able to clear the runway of
  personnel and equipment, if necessary. At times air traffic control and
  /or the pilots may not be aware about a runway closure at the
  non-towered airport. That is, sometimes a NOTAM is issued after an
  airplane becomes airborne and the pilot did not receive the latest
  update, especially at an uncontrolled airfield.

  -----------------------------------------------------------------------

d.  Include special snow crew communication procedures for "whiteout"
    conditions at both towered and non-towered airports.

e.  Include special snow crew communication procedures for occasions
    when a single equipment operator needs to return to the runway after
    a major clearing event.

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6.  []{#__RefHeading___Toc213137125 .anchor}**Staff Training and
    Recordkeeping.** The SICP should describe qualification criteria and
    training for individuals directly involved in snow and ice control
    operations. That is, the SICP might specify that an implemented
    training program contain specific course material for equipment
    drivers, staff working in the Snow Control Center, etc. The SICP
    should also outline recordkeeping procedures for tracking employee
    progress in achieving training goals and objectives. Although
    airport operators should develop their own training programs to
    address conditions at their particular airports, the FAA recommends
    the programs contain the following minimum components:

    a.  Use of formal classroom lectures, training films if available,
        and discussion periods to teach the contents of the SICP to
        individuals who need to understand procedures in detail.

    b.  Conduct of tabletop exercises that use miniature equipment on
        airfield layouts to simulate operations.

    c.  Hands-on training for equipment operators on how their equipment
        works as well as practice runs under typical operational
        scenarios.

    d.  Instruction on airfield familiarization that includes both day
        and night tours of the airfield and ensures an understanding of
        all surface markings, signs, and lighting.

    e.  Instruction for all personnel on proper communication procedures
        and terminology. This includes the special procedures to be
        followed during "whiteout" conditions and when radio signal is
        lost between drivers and/or the ATCT. See FAA AC 150/5210-20,
        *Ground Vehicle Operations on Airports,* for guidance on
        communication procedures for airport personnel.

    f.  Instruction for drivers on the proper procedures and
        communications to follow when the ATCT is not operating or the
        airport has no ATCT.

    g.  Training in following runway closure criteria for personnel
        responsible for closing and opening runways during snow events.
        This training is especially important for non-towered airports
        or part-time towered airports.

7.  []{#__RefHeading___Toc213137126 .anchor}**Other Related Items.** The
    implemented SICP needs to take into account how the document will
    integrate with other airport plans, programs, and lease agreements.

    a.  **Other Airport Plans and Programs.** Although the SICP is a
        stand-alone plan, it should integrate with other airport plans
        and programs to avoid conflicts and duplication of procedures
        and responsibilities. A few examples of closely related
        plans/programs are the *Airport Certification Manual*, *Airport
        Emergency Plan,* and the *Storm Water Pollution Prevention Plan*
        (for deicer runoff mitigation). The FAA recommends the airport
        fire fighting and rescue service receive a copy of the SICP for
        their familiarization, especially so responders will know which
        service roads will be closed.

    b.  **Post Accident/Incident Recommendations.** To address accidents
        or incidents that might occur during adverse weather conditions,
        the SICP should contain procedures that ensure surface
        conditions occurring during the event are properly inspected and
        documented. Additionally, the airport operator must not disturb
        evidence on the runway until the appropriate Federal authority
        (FAA/National Transportation Safety Board (NTSB) provides a
        release. To help NTSB, the airport operator should document the
        type and depth of contamination on the runway at the time of the
        accident/incident, which should include conducting a runway
        friction assessment and taking still and/or video photography.
        If wreckage is observed on the pavement, the airport operator
        must not attempt to conduct testing in those areas that would
        disturb evidence on the runway (see AC 150/5200-12, *Fire
        Department Responsibility in Protecting Evidence at the Scene of
        an Aircraft Accident*).

    c.  **Snow and Ice Control Contractors/Lease Agreements.** The
        principle of ensuring safety of operations applies equally to
        lease holders and service contractors hired to perform snow and
        ice control services. In particular, contractual agreements
        should be clear and specific in terms of duties, procedures for
        snow and ice control, responsibilities for communications and
        ground control, and other contingencies. Service contractors and
        leaseholders should receive a copy of the latest airport SICP,
        not necessarily the complete *Airport Certification Manual.*
        Contracted service providers are recommended to have similar
        training as described in Paragraph 2-6(a) -- (f).

    d.  **Storm Water Runoff Regulations.** Greater emphasis has been
        placed on mitigating the negative impacts associated with snow
        clearing operations and equipment maintenance on bodies of water
        off the airport. The SICP should be reviewed and modified, if
        necessary, to ensure it complements the airport's storm water
        discharging permit. That is, the SICP should help the airport
        operator achieve compliance with Federal, state, and local
        environmental storm water runoff regulations.

# Chapter 3. Snow Clearing Operations and Preventive Measures

1.  []{#__RefHeading___Toc213137128 .anchor}**Weather Forecasting.**
    Appropriate responses to a winter storm event begin with accurate
    and timely weather information. A reliable weather forecast not only
    enhances the effectiveness and efficiency of any SICP, but it offers
    airport operators operational cost savings associated with snow
    clearing tasks, chemical usage, and staffing. Airport operators
    should base their snow clearing operations or preventive measures on
    weather forecasting that offers continuous, up-to-date, and airport
    weather-related information. The FAA recommends that airport
    operators select a weather forecasting approach that offers usable
    information to airport users as well as to the airport operator. One
    such approach, the *Weather Support to Deicing Decision Making
    (WSDDM) System*, is described below.

2.  []{#__RefHeading___Toc213137129 .anchor}**FAA Forecasting Research
    and Development for Airport Operators.** The FAA Aviation Weather
    Research Program began research in the 1990s to fully understand the
    safety problems faced during winter storm events and to improve
    decision making by airport operators and air carrier ground
    operations during these events. The research resulted in the
    *Weather Support to Deicing Decision Making (WSDDM) System,* an
    integrated display system that depicts accurate, real-time
    determinations of snowfall rate, accumulations and their liquid
    equivalents, temperature, humidity, wind speed, and direction of
    storm events.

    a.  **Weather Support to Deicing Decision Making (WSDDM) System.**
        The WSDDM System is an automated system that analyzes and
        forecasts short-term winter weather conditions within the
        airport vicinity. The data inputs to the system are provided by
        snow gauges; weather radars, such as Doppler; surface weather
        stations; and National Weather Service Aviation Routine Weather
        Report (METAR) data from Automated Surface Observing Systems
        (ASOS). All data are processed by software algorithms to produce
        a graphical and text depiction of current weather conditions and
        a 1-hour forecast of expected snowfall rate and accumulation at
        the airport. The displayed analyses and forecasts can be easily
        understood by most users. The graphical data can be generated
        and displayed on a local computer or viewed online. The system
        has been effective at major U.S. airports.

The basic version of the WSDDM system, known as Basic WSDDM, is for
unidirectional storm fronts. The system has a single snow gauge with a
computer display of the current and historical liquid equivalent
snowfall rates and accumulation. Airports that routinely encounter
multiple storm fronts should use two or more snow gauges. Figure 3-1
shows one type of snow gauge used by WSDDM. Figure 3-2 illustrates the
Basic WSDDM schematic for a unidirectional storm configuration.

WSDDM systems must comply with the equipment performance and
installation requirements described in Society of Automotive Engineers
(*SAE) Aerospace Standard (AS) 5537, Weather Support to Deicing Decision
Making (WSDDM), Winter Weather Nowcasting System*. The SAE specification
is available for purchase at [http://www.sae.org](http://www.sae.org/).

b.  **Safety and Operational Benefits.** The WSDDM system provides
    current and 1‑hour NOWCAST forecasts (current conditions) of snow
    bands and surface weather conditions on the airport and the
    surrounding 125-mile (200-km) vicinity. The display is optimized to
    allow airport operators and air carriers to understand (typically
    within 1 minute) the current weather conditions at the airport and
    in the surrounding region. This capability allows for more rapid and
    appropriate decision making during winter storms with minimal impact
    on airport resources and staff workload.

![](media/image4.jpeg){width="3.283333333333333in" height="2.475in"}

[]{#__RefHeading___Toc212272466 .anchor}Figure 3-1. Single Alter Wind
Shield Type

![](media/image5.png){width="3.4972222222222222in"
height="4.196527777777778in"}

[]{#__RefHeading___Toc212272467 .anchor}Figure 3-2. Schematic of
Unidirectional Storm WSDDM Configuration

1.  **Benefits to Airport Operator**s. Users of WSDDM have reported
    various operational and cost-saving benefits. WSDDM optimizes runway
    clearing operations by providing airport operators more accurate
    information about when a snow band will affect the airport. Accurate
    timing saves on anti-icers because it allows crews to apply them
    according to the manufacturer's recommended lead times. In terms of
    managing crew workloads, WSDDM determines gaps in storm events,
    which can be used to change crew shifts, take rests, and refill
    chemical trucks, sand spreaders, and other equipment. Airport
    operators are also able to more accurately determine when the
    airport can resume normal operations by examining the radar loops
    and storm tracks and watching storm trends. By examining the storm
    tracks, users can make fairly accurate 3- to 4-hour forecasts of
    snow onset, which, in turn, allow airport operators to prepare more
    appropriately for winter storms.

2.  **Real-Time Liquid Content Forecast.** A key safety element of the
    WSDDM system is the use of one or more precision snow gauges. These
    snow gauges provide real-time estimates of the liquid equivalent
    snowfall rate for every minute. This measurement is key to air
    carrier deicing operations because the deicing community has shown
    *the liquid equivalent snowfall rate is the key factor leading to
    the failure of deicing/anti-icing fluids.* The current National
    Weather Surface METAR stations do not provide this data. Instead,
    METAR provides hourly snow intensity estimates based on
    *visibility.* Snow intensity estimates based on visibility have been
    shown to be misleading when wet snow, heavily rimed snow (snow that
    has accreted significant amounts of cloud droplets), and snow
    containing single crystals of compact shape (nearly spherical)
    occur. Researchers define the hazard as
    high-visibility/high-snowfall rate conditions. Recent examination of
    five of the major airplane ground deicing accidents showed that high
    visibility-high snowfall rate conditions were present during a
    number of these accidents. All of the accidents had nearly the same
    liquid equivalent rate of 0.1 inch/hour (2.5 mm/hour), but widely
    varying visibilities. The WSDDM System was designed to address this
    safety concern by including snow gauges to measure liquid equivalent
    snowfall rate every minute.

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3.  []{#__RefHeading___Toc213137130 .anchor}**Forecasting Runway Surface
    Conditions.** One proven method of forecasting the surface
    conditions of runways is to use runway surface condition sensors
    (RSCS). Two basic types of RSCS are in use today, namely in-pavement
    stationary sensors and vehicle-mounted infrared sensors. The safety
    benefit of RSCS is their predictive capability for proactive
    anti-icing decision making. Since the temperature of pavements lag
    behind air temperature, the use of air temperature to infer surface
    conditions is imprecise. Therefore, the use of air temperature is
    never recommended because it frequently leads to misinformation
    about the true behavior of pavement surfaces. This inaccuracy can
    result in inappropriate airfield clearing operations or poorly timed
    preventive measures. At its worst, this misinformation might result
    in delays that allow ice to bond to paved surfaces, the hardest
    condition to rectify. With the exception of freezing rain, ice will
    not form on pavements unless the pavement temperature itself reaches
    the freezing point. Therefore, knowledge of the direction and rate
    of temperature change within a pavement structure provides the
    predictive capability as to when to expect the formation of ice. The
    predictive nature of RSCS is particular valuable as it ensures the
    timely application of anti-icing (or deicers) chemicals, which
    provides a cost savings in chemicals, and helps crews make
    appropriate chemical selections to prevent, weaken, or disbond ice
    or compacted snow from paved surfaces. Airport operators have at
    their disposal in-pavement RSCS at pre-determined sites and mobile
    RSCS that are hand-held or vehicle-mounted to evaluate any pavement.

    a.  **Stationary Runway Weather Information Systems.** These
        stationary sensors provide only site-specific pavement and air
        temperature trends, dew point temperature, chemical strength,
        and other atmospheric weather conditions at the installation
        sites. Sensor information is generally disseminated via a
        central computer to airport users. An added bonus of in-pavement
        RSCS is their ability to predict when previously applied
        chemicals have been diluted sufficiently to require
        reapplication of chemicals. The FAA recommends that in-pavement
        RSCS comply with the performance and installation requirements
        of *SAE Aerospace Recommended Practice (ARP) 5533, Stationary
        Runway Weather Information System (In-pavement)*. The SAE
        specification is available for purchase at
        [http://www.sae.org](http://www.sae.org/).

    b.  **Mobile Infrared Surface and Ambient Temperature Sensor
        Systems.** These vehicle-mounted sensors provide pavement and
        air temperatures at any desired airfield pavement location.
        Information is disseminated directly to the viewer or driver of
        the vehicle-mounted units. Presently, *SAE G-15,* *Airport Snow
        and Ice Control Committee*, is in the process of finalizing *SAE
        ARP 5623, Mobile Infrared Runway Surface and Digital Ambient
        Temperature Sensor Systems*. Until finalized, FAA recommends
        that mobile RSCS comply with the performance requirements
        specified by the United States Air Force specification. The SAE
        specification, once finalized, will be available for purchase at
        [http://www.sae.org](http://www.sae.org/).

# Chapter 4. Snow Clearing Operations and Ice Prevention

1.  []{#_Ref213137814 .anchor}**Introduction.** Snow, slush, ice, and
    standing water on a runway impede airplane acceleration by absorbing
    energy in compaction and displacement, and by impinging on parts of
    the airplane after being kicked up by the tires. For airplanes
    decelerating, slush, snow, and standing water-covered pavements and,
    especially iced surfaces, hamper deceleration rates due to a
    reduction in the friction coefficient of the runway and the
    potential for hydroplaning. Large chunks of ice, from refreezing
    snow or slush, or deposited from aircraft gear during landings, can
    cause severe damage to tires, engines and airframes. Wet snow,
    slush, and standing water on a runway can also limit operations due
    to potential structural damage caused by the contaminants impinging
    on the airplane at high speed. Although the limits vary for
    different airplanes, most transport category airplanes are
    prohibited from operating on runways covered by more than ½ inch of
    wet snow, slush, or standing water (see AC 91-6A, *Water, Slush, and
    Snow on the Runway.*) Consequently, these runway surface
    contaminants should be minimized to maintain safe landing, takeoff,
    and turnoff operations. For these reasons, snow clearing operations
    for Priority 1 runway(s), taxiway connectors, and taxiways to the
    terminal(s) should start as soon as possible after snowfall or icing
    begins. One prime goal is to take the appropriate measures so snow
    in its various forms, such as slush or frozen water, does not bond
    to the pavement. Dry snow falling on cold dry pavements will
    generally not adhere and may be blown off by wind or airplane
    operations or removed by brooming operations. In such conditions,
    only brooming may be needed to prevent the formation of compacted
    snow tracks. Snow fences may be of use to airports that primarily
    experience dry snowfalls. Wet snow, however, cannot be blown off the
    pavement and will readily compact and bond to it when run over by
    airplane wheels. Consequently, the airport operator will need to
    implement different clearing and/or preventive measures for wet snow
    than those used for dry snow conditions. When measures are taken,
    the airport operator's Snow Control Center (SCC) must (1) maintain
    close coordination with the ATCT and the Flight Service Station
    (FSS) or UNICOM to ensure prompt and safe responses to winter storm
    events and (2) inform the users of the airport when less than
    satisfactory conditions exist.

2.  []{#fourtwo .anchor}**Snow Clearing Principles**. Winter conditions
    and rates of accumulations of precipitation vary widely from airport
    to airport. However, there are some basic guidelines that apply to
    all airports that should be followed as closely as possible. The
    airport operator should notify airport users promptly and issue a
    NOTAM advising users of unusual airport conditions. Wind speed and
    direction, available equipment, and local conditions that may
    require special equipment and techniques collectively determine the
    snow clearing procedures for the airport's SICP. The following
    guidance offers a generic outline for writing the SICP that covers
    ramp/terminal-related items and runway/taxiway-related items.

    a.  Ramp and Terminal **--** Clearing Objectives. Accumulations of
        snow and slush, snow tracks, and thin layers of ice on ramps and
        airplane parking areas, including holding areas, can make for
        safety hazards. The SICP should contain measures to mitigate at
        least the following four common situations:

        1.  **Slick Ramp Surfaces.** Ramp equipment and ramp personnel
            operating on slick or icy ramp surfaces lack sufficient
            traction to start, stop, or even remain in place when
            encountering jet exhaust from surrounding airplanes.
            Maintaining good traction is critical to the safety of
            personnel, equipment, and airplanes.

        2.  **Increased Airplane Engine Thrust.** Pilots of parked or
            holding airplanes must apply increased engine thrust to
            break away, maneuver, and taxi under adverse ramp surface
            irregularities, such as frozen ruts formed by tire tracks.
            The resultant excessive engine blast necessary to overcome
            such obstacles may damage other airplanes, ramp equipment,
            or ramp personnel.

        3.  **Obscured Taxi Signage.** The clearing of snow from ramp
            areas must not be performed in a way that partially or
            completely covers taxiway signs leading to the airfield with
            plowed snow*. Observing this precaution will reduce the risk
            of runway incursions.*

        4.  **Obscured Terminal Visual Aids.** The obscuration of
            normally visible surface markings or obliterated sign
            messages could make maneuvering on ramps difficult and slow.
            Pilots, unable to see these visual aids, are hard pressed to
            judge direction and taxiing clearances.

        5.  **Snow Stockpiles Adjacent to Airplane Operating Areas.**
            Airport operators should exercise care when moving snow from
            the ramps and terminals toward taxiways and runways.
            Depending on the amount of snow cleared and the size of the
            ramp, ramp signage directing pilots toward the runway could
            become obscured (covered with snow), and the resulting
            height of snow stockpiles could cause a clearance issue
            between taxiing airplanes and the snow stockpile. Airports
            that experience heavy snowfalls and have large ramps with
            limited space for stockpiling snow should consider operating
            snow melters or hauling snow away.

    b.  **Runway and Taxiway Suggested Clearing Objectives.** The
        following guidance should not be interpreted to require specific
        equipment at any airport. It is presented to show efficient use
        of various equipment to optimize snow clearing operations. Some
        types of equipment may not be appropriate for some airports.
        Equipment and procedures used must be determined based on many
        factors, including but not limited to climate, number and types
        of operations, airport staffing, and the airport budget.

        1.  Focus runway snow clearing operations on keeping the entire
            primary runway(s), as near as practicable, bare from snow
            accumulations or ice buildup. Depending on precipitation
            rate, the time required to clear the full width of the
            runway may result in additional accumulation, and thus less
            braking capability, on the critical center portion. In such
            a case, concentrating clearing operations on the center
            portion can result in greater safety. The minimum width
            required will vary by airplane type, but is generally 100'
            for transport category airplanes. The airport operator
            should check with airport users regarding their minimum
            runway width requirements.

        2.  Depending on the equipment fleet, etc., some operations will
            start at the center of the runway and work outward to the
            shoulders.

        3.  Use sweepers or brooms initially to keep the primary runway
            or its center portion, as near as practicable, bare of
            accumulations. Also, when snow has melted or ice begins to
            separate from the pavement due to the action of chemicals,
            sweepers or brooms should be used to remove the residue. As
            soon as snow has accumulated to a depth that cannot
            efficiently be handled by the sweepers or brooms,
            displacement plows and rotary plows (snow blowers) should be
            used as follows.

            i.  Use displacement plows, in tandem if more than one, to
                windrow snow into a single windrow that can be cast over
                the edge of runway lights by a rotary plow.

            ii. For runways or other paved areas with in-pavement
                surface condition sensors, remove any snow or ice that
                affects the performance of the remote sensors.

            iii. Regarding the use of displacement plows, ice and snow
                 will always melt around runway centerline and touchdown
                 zone light assemblies. However, under cold
                 temperatures, ice rings, termed "igloos," tend to form
                 around them. In order to prevent damage to lights, use
                 appropriate polyurethane cutting edges or shoes and
                 casters on plow moldboards and on the front of rotary
                 plows.

            iv. Rotary plows should throw snow a sufficient distance
                from runways/taxiways edges so adequate clearance is
                available between airplane wings and engine nacelles and
                the cast snow banks. Figure 4-1 shows desired maximum
                snow height profiles, which are based on airplane design
                groups.

        4.  Obscured visual aids---in particular in-pavement and edge
            lights, taxiways, runway markings (such as touchdown
            marking), airport guidance signs, and runway end
            identification lights (REIL), precision approach path
            indicator (PAPI) or visual approach slope indicator (VASI)
            --- need to be maintained free of snow and ice.

        5.  All drivers must maintain a safe distance between equipment
            operating in echelon (i.e., V-formation, close wing
            formation) in order to avoid accidental contact or
            accidents.

        6.  A covering of snow and ice or drifts may affect visual and
            electronic NAVAIDs. Any snow or ice that affects the signal
            of electronic NAVAIDs should be removed. When clearing with
            rotary plows and displacement plows, special procedures need
            to take into account the location of all NAVAIDs, especially
            to protect the guidance signal of instrument landing systems
            (ILS). The SICP needs to address the following situations:

            i.  Glide slope critical ground areas along the runway
                require that snow depths be limited in height to prevent
                signal loss or scattering. Figure 4-2 provides graphic
                representations of the glide slope ground snow clearance
                areas with prescribed snow depth limitations according
                to type of facility and aircraft approach category. When
                snow depths exceed the specified depth limitations,
                minima are raised to the "localizer only" function until
                the conditions revert or are corrected. Two consecutive
                pilot reports of glide slope signal malfunctions
                generally result in raised minima (a NOTAM must be
                issued by the owner of the NAVAID). A few additional
                points should be considered. First, the 200-foot width
                dimension adjacent to the threshold might be wider for
                an antenna mast placed further out (see FAA Order
                6750.49, *Maintenance of Instrument Landing System (ILS)
                Facilities*). Second, the snow clearance areas
                illustrated in the figures are minimal in size. Third,
                snow clearing activities should not allow snow banks,
                mounds, or ridges exceeding 2 feet to be placed along
                the edges of the prescribed snow clearance areas.
                Fourth, snow banks should not be placed off the approach
                ends of runways, especially for CAT II/III operations.

  -----------------------------------------------------------------------
  **Note**: Snow banking operations need to take into account the
  guidance in Figure 4-2.

  -----------------------------------------------------------------------

ii. Visibility of signs (legibility) and lights should be maintained by
    certain prescribed clearing techniques or by performing
    post-clearing maintenance. Maintaining visibility can be better
    achieved by taking into account wind directions. For example, in
    crosswind conditions, cast in the downwind direction. Figures 4-3
    through 4-5 provide general guidance.

iii. The snow depth height limitations noted in Figure 4-2 do not take
     into consideration airplane characteristics. That is, at some
     airports, airplane characteristics, such as engine clearances, may
     dictate lower snow banks than shown in Figure 4-2. The objective
     here is prevention by avoiding the introduction of hazardous snow
     banks, drifts, windrows, and ice ridges that could come into
     contact with any portion of the airplane wing or nacelle surface.

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7.  Upon completion of snow clearing operations, runway friction
    measurements should be taken to assess the effectiveness of the snow
    clearing operation. See Chapter 5 for recommended procedures.

8.  If the airport's operation involves the use of snow banks, their
    height profiles should be compatible with NAVAID ground requirements
    and offer sufficient clearance between airplane wings and engine
    nacelles to avoid structural damage to jet and propeller airplanes.
    Figure 4-1 shows desired maximum snow height profiles, which are
    based on airplane design groups (see AC 150/5300-13, *Airport
    Design*, for airplane design group categories.) Snow banking along
    terminal or cargo aprons likewise should comply with Figure 4-1 to
    prevent operational problems caused by ingestion of ice into turbine
    engines or by propellers striking the snow banks. Appendix 1, which
    used numerous airplane models, was used to develop criteria for
    figure 1.

9.  If the runway pavement temperature is warm enough for snow to
    compact and bond or if freezing rain is forecasted, approved
    anti-icing chemicals and/or heated sand should be applied prior to
    the start of precipitation or as soon as precipitation starts. Some
    airport operators prefer to apply deicing chemicals rather than
    anti-icing chemicals for different weather conditions. Paragraph 4-6
    provides a listing of approved fluid and solid material
    specifications.

10. All snow removal units operating in aircraft movement areas must
    maintain radio communication with the ATCT, if one exists, or be
    under the direct control of a designated supervisor who in turn is
    in direct communication with the ATCT.

11. High-speed runway turnoffs require the same attention for ice and
    snow control and removal as runways. These turnoffs should offer
    sufficient directional control and braking action for airplanes
    under all conditions. Accident data clearly illustrate that poor
    attention to high-speed runway turnoffs contributes to veer offs.

12. Joint-use airports with military operations may have arresting
    barriers located near the end of the runway or at the beginning of
    the overrun areas. Great care should be taken in clearing snow from
    the barriers. Barriers located on the runway should be deactivated
    and pendants removed prior to snow removal operations. Snow should
    be removed to the distance required for effective run-out of the
    arresting system.

![](media/image6.wmf){width="5.472916666666666in"
height="6.971527777777778in"}

[]{#__RefHeading___Toc212272468 .anchor}Figure 4-1. Snow Bank Profile
Limits Along Edges of Runways and Taxiways with the Airplane Wheels on
Full Strength Pavement (s**ee F**igure 4-2 guidance)

![](media/image7.wmf){width="6.025in" height="8.129861111111111in"}

[]{#__RefHeading___Toc212272469 .anchor}Figure 4-2. ILS CAT I and CAT
II/III Snow Clearance Area Depth Limitations

![](media/image8.wmf){width="4.7756944444444445in"
height="3.248611111111111in"}

![](media/image8.wmf){width="3.722916666666667in" height="0.84375in"}

[]{#__RefHeading___Toc212272470 .anchor}Figure 4-3. Possible Team
Configuration with Perpendicular Wind

(Dependent upon Rotary Plow performance)

![](media/image9.wmf){width="4.3277777777777775in"
height="2.6215277777777777in"}

![](media/image9.wmf){width="3.670138888888889in"
height="0.8118055555555556in"}

[]{#__RefHeading___Toc212272471 .anchor}Figure 4-4. Possible Team
Configuration During Light Snowfall with Parallel or Calm Wind

(Dependent upon Rotary Plow performance)

![](media/image10.wmf){width="5.064583333333333in"
height="2.9027777777777777in"}

[]{#__RefHeading___Toc212272472 .anchor}Figure 4-5. Possible Team
Configuration During Medium to Heavy Snowfall with Parallel or Calm Wind
(Dependent upon Rotary Plow performance)

c.  **Surface Incident/Runway Incursion Mitigation Procedures.** The FAA
    strongly recommends the SICP contain specific safety procedures or a
    separate written section to mitigate the possibility for surface
    incident/runway incursions. These specific safety procedures should
    provide answers to, at minimum, the following two questions: (1) How
    can pilots of small or large airplanes or vehicle drivers traversing
    the airfield cause a runway incursion because of our snow clearing
    operations? and (2) How do snow operation personnel at either
    non-towered airports or airports with less than 24-hour ATCTs
    monitor information released by the ATC enroute center? The
    procedure addressing the latter questions should apply even if a
    NOTAM has been issued closing the runway for snow clearing
    operations. This precaution is especially important during marginal
    visual meteorological condition (VMC). The SICP should address the
    following topics:

    1.  **Radio Communications.** Equipment operations must be timed
        carefully and coordinated properly with team members to ensure
        an orderly turnaround for safe return and start of a new pass.
        The SICP should designate a lead operator for each shift who
        maintains contact with his team members and the ATCT. At
        airports lacking an ATCT or when the tower is closed, proper
        radio communications must be maintained at all times and in
        accordance with SICP procedures. Consideration should be given
        to providing vehicle operators with headphones to minimize
        ambient noise disruption from vehicular noise.

    2.  **Failed Radio Signals.** The SICP must outline specific
        procedures when radio signal is lost between crews and when a
        single driver loses radio signal. All drivers must be trained in
        the specific procedures to follow.

    3.  **Airfield Signage and Lights.** Airfield and ramp signs must be
        kept clean of plowed or cast snow to maintain the legibility of
        signage. Priority should be given to lights and signs associated
        with holdlines, direction and location signs, and ILS critical
        areas. Common methods to remove snow from signs include using a
        truck mounted with an air-blast unit, spraying the faces of
        signs with an approved liquid deicer, or hand shoveling.

    4.  **Low Visibility and Whiteouts.** It is of utmost importance to
        maintain visual contact with your surroundings during snow
        clearing operations, especially for operations in an echelon
        formation. The SICP must specify procedures to follow if
        visibility suddenly drops to near zero or whiteout conditions
        exist while clearing operations are in progress. For example,
        the airport operator may require that all equipment stop
        immediately with all drivers radioing in their positions to the
        designated supervisor or to ATCT for runway evacuation
        instructions.

    5.  **Driver Fatigue.** Consideration should be given to monitoring
        the *"windshield time"* of drivers (length of shift) operating
        snow removal equipment because operator fatigue could become a
        contributing factor for runway incursions. In response, some
        airport operators have implemented limits on driver operating
        hours.

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3.  []{#__RefHeading___Toc213137134 .anchor}**Controlling Snow Drifts.**
    Preventing snow from drifting onto operational areas at airports
    receiving severe winter storms reduces the duration and frequency of
    snow clearing operations. Two methods for controlling drifts are
    described below.

    a.  **Snow Fences.** Snow fences that are properly designed and
        located can reduce windblown snow across airfields. Experience
        at a particular airport is the most helpful in determining
        optimum locations for snow fences. The following precautions and
        guidance are provided:

        1.  Prior to any installations, the airport operator must
            contact the nearest Air Traffic technical operations control
            center of any planned installations in the vicinity of a
            NAVAID system. Failure to remove snow or the introduction of
            snow in areas adjacent to NAVAID systems could result in
            erroneous signal guidance or facility shutdown.

        2.  Snow fences should be located upwind of the area to be
            protected.

        3.  A study conducted by the U.S. Department of Agriculture
            showed 12-foot (3.7-m) high fences were generally most
            effective. Shorter heights can be and usually are necessary
            on airport property, since snow fences must not penetrate
            any critical surfaces or be located inside the runway safety
            area or the runway object free area, as defined in AC
            150/5300-13.

    b.  **Snow Trenches.** Snow trenches that catch and store drifting
        snow have been used at times by airports with heavy snowfalls.
        This approach is considered an expedient way to control snow
        from drifting after it has been cleared to the edge of the
        runway. Multiple trenches spaced longitudinally about 10 feet
        (3 m) apart running parallel to the runway can store more snow.
        A trench should be excavated no closer than 50 feet (15 m) from
        the runway. Figure 4-6 illustrates typical snow trench formation
        relative to wind direction.

![](media/image11.wmf){width="5.183333333333334in"
height="3.0236111111111112in"}

[]{#__RefHeading___Toc212272473 .anchor}Figure 4-6. Typical Snow Trench
Dimensions

4.  []{#__RefHeading___Toc213137135 .anchor}**Snow Disposal.** The SICP
    should also specify how and where large quantities of snow are to be
    disposed. Two common approaches are as follows:

    a.  **Melting Pits or Portable Melters.** A variety of snow and ice
        melters are in use at various airports that deal with large snow
        falls and for the environmental mitigation of deicer chemicals.
        This approach may be an economical viable solution to expensive
        snow hauling services. In contrast, melters eliminate the need
        for convoys of trucks to enter and exit secured airport areas,
        i.e., a lesser security risk. Environmentally, contaminates
        within the snow are retained for proper disposal. Portable
        melters in comparison to melting pits can be conveniently setup
        at various melting sites instead of having to transport
        collected snow to a designated snow hauling area(s).

    b.  **Identifying Disposal Sites.** If there is insufficient space
        for storing snow near areas to be cleared and no melting or
        flushing means are available, hauling to a disposal site may be
        necessary. If deemed necessary, the disposal site should be
        selected before winter sets in and identified in the SICP. The
        selection process should at least consider the following: (1)
        disposal sites do not compromise airplane operations, airport
        NAVAIDs, airport traffic, and ATCT operations such as ATCT
        line-of-sight requirements; (2) sites have adequate drainage
        capability; and (3) sites offer, if required, environmental
        mitigation of captured chemicals.

5.  []{#__RefHeading___Toc213137136 .anchor}**Methods for Ice Control
    and Removal.** Preventing a bond from occurring between ice and the
    pavement surface is always preferred over the mechanical removal or
    melting of the bonded ice. Appendix 2 provides the characteristics
    of ice and other forms of snow and other details about handling
    problems. Paragraph 4-6 provides the FAA-recommended chemical
    specifications for approved airside anti-icer and deicer products.
    Prevention is achieved by applying *approved* anti-icing chemicals
    to pavements with temperatures expected to go below 32° F (0° C).
    Fluid anti-icing products instead of solid anti-icing products are
    recommended since the liquid form is more effective in achieving
    uniform distributions and improved chemical-adhesion to the pavement
    surface. The primary drawback of solid chemicals on cold pavements
    is their inability to adhere properly to the surface, which can lead
    to their being windblown or scattered about.

Once the ice has bonded to the pavement surface, the airport operators
may use approved deicers to melt through the ice pack to break up or
weaken the ice bond; increase the frictional characteristics of the
surface, for example, by applying heated sand; or use mechanical means,
such as plowing with under-body scrapers or scarifying the ice surface
to break the ice packs. The type of brooms used to remove a layer of ice
is important since in some cases the broom may actually "polish" the
ice, thus reducing traction. Steel bristles are better than poly
bristles since one "cuts" the ice surface while the other "flips" snow.
Paragraph 4-7 provides guidance on methods to improve the frictional
characteristics of surfaces, and Paragraph 4-8 provides the FAA
recommended sand gradation for runway and taxiway usage.

6.  []{#__RefHeading___Toc213137137 .anchor}**Approved Chemicals.**

    a.  **Airside Chemicals.** The FAA either establishes approval
        specifications or, upon acceptance, references the
        specifications of professional associations, such as SAE
        Aerospace Material Specifications (AMS), and the U.S. military
        (MIL-SPEC). The approved airside chemicals for runway and
        taxiway applications are fluid and solid products meeting a
        generic SAE or MIL specification. These specifications require
        vendors to provide airport operators with a lab certification
        stating the chemical conformed to the applicable specification
        and a material safety data sheet (MSDS) for handling the
        product. With the increased accountability placed on airport
        operators to manage deicing/anti-icing chemical runoff, they
        should request vendors to provide certain environmental data.
        These data consist of information on pollutants the
        Environmental Protection Agency and the State Department of
        Natural Resources request of the airport operators in their
        discharge reporting requirements. Typically, the information
        includes percent product biodegradability, biochemical oxygen
        demand (BOD~5~), chemical oxygen demand (COD), pH, presence of
        toxic or hazardous components, if any, and remaining inert
        elements after application. MSDSs provide measures on how to
        secure large product spills and a 24-hour toll-free emergency
        phone number. While these fluid and solid specifications cover
        technical requirements for deicing/anti-icing products, they do
        not address the compatibility issue of combining products during
        operations. Airport operators, therefore, should query
        manufacturers about the safe and proper use of concurrently
        applying multiple deicers/anti-icers. The FAA-approved airside
        chemical specifications, which may be restricted by state or
        local environmental regulations, are as follows:

        1.  **Fluid Deicer/Anti-icers.** The approved specification is
            SAE AMS 1435*, Fluid, Generic Deicing/Anti-icing, Runways
            and Taxiways*. Approved products include glycol-based
            fluids, potassium acetate base, and potassium formate-based
            fluids**.** The SAE specification is available for purchase
            at [http://www.sae.org](http://www.sae.org/). Application
            rates for a specific product are based on manufacturer
            recommendations. In terms of material cost-savings, less
            product is used by anti-icing operations than by deicing
            operations.

        2.  **Solid Deicer/Anti-icer.**

            i.  **Generic Solids.** The approved specification is SAE
                AMS 1431A*, Compound, Solid Runway and Taxiway
                Deicing/Anti-icing*. Approved solid compounds include
                airside urea, sodium formate, and sodium acetate. It is
                noted that, in comparison to airside urea, sodium
                formate and sodium acetate products continue to be
                effective for much colder pavement temperatures. The
                urea deicing function is practical only at temperatures
                above approximately 15° F (-10° C) because of the
                decreasing melting rates below this temperature value.
                The decreasing melting rate is a result of urea's
                eutectic temperature, defined in Paragraph 1-9, which is
                approximately 11° F (-12° C). However, the presence of
                solar radiation assists urea in the melting action.
                Pavement surface temperature and ice thickness determine
                the urea application rate. Application rates for a
                specific product are based on manufacturer
                recommendations.

            ii. **Airside Urea (or "Carbamide"**)**.** The approved
                specifications are SAE AMS 1431A*, Compound, Solid
                Runway and Taxiway Deicing/Anti-icing,* and MIL SPEC
                DOD-U-10866D, *Urea-Technical*. Agricultural grade urea
                that meets any of these specifications, called airside
                urea, is acceptable. This nontoxic solid white chemical
                comes in either powder or "shotted" ("prilled") form.
                The latter form's shape is small spheres of about l/l6
                inch (1.5 mm) in diameter. Both forms are primarily for
                deicing, where powdered urea is frequently mixed with
                sand. Hot mixtures of powder or "shotted" urea and sand
                are used by airport operators for two purposes: (1)
                immediate increase in braking action and (2) retention
                of chemical over the pavement area until it initially
                dissolves some of the ice and then melts the remainder.
                Table 4-1 provides guidance on application rates in
                relation to pavement temperature and ice thickness.

[]{#__RefHeading___Toc212274680 .anchor}Table 4-1. Guidance for Airside
Urea Application Rates

+-----------------+-----------------+-----------------+-----------------+
| **Ice           | **Temperature   |                 |                 |
| Thickness**     | Degree F (ºC)** |                 |                 |
|                 |                 |                 |                 |
| **Inch (cm)**   |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
|                 | **30 (-1.1)**   | **25 (-3.9)**   | **20 (-6.7)**   |
+-----------------+-----------------+-----------------+-----------------+
| Less than 1/32  | 0.016 (0.078)   | 0.023 (0.11)    | 0.06 (0.29)     |
| (0.08)          |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| 1/32 up to but  | 0.03 (0.15)     | 0.06 (0.29)     | 0.125 (0.61)    |
| not including   |                 |                 |                 |
| 1/8             |                 |                 |                 |
|                 |                 |                 |                 |
| (0.08 - 0.32)   |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| 1/8 (0.32) to   | 0.125 (0.61)    | 0.175 (0.86)    | 0.275 (1.34)    |
| 1/4             |                 |                 |                 |
|                 |                 |                 |                 |
| (0.32 -- 0.64)  |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+

b.  **Landside Chemicals.** The most effective landside chemicals used
    for deicing/anti-icing in terms of both cost and freezing point
    depression are from the chloride family, e.g., sodium chloride (rock
    salt), calcium chloride, and lithium chloride. However, ***these
    chemicals are known to be corrosive to aircraft and therefore are*
    *prohibited for use on aircraft operational areas***. When any
    corrosive chemical is used, precautions should be taken to ensure
    that (1) vehicles do not track these products onto the aircraft
    operational areas and (2) chemical trucks used for transporting
    corrosive chemicals are cleaned prior to transporting airside
    chemicals or sand. It is noted that although the solids sodium
    acetate and sodium formate and the fluids potassium acetate and
    potassium formate products are classified as salts, those that
    contain corrosion inhibitor packages to comply with an SAE
    specification are approved for airside applications.

c.  **Environmental and Pavement Aspects of Anti-icing and Deicing
    Chemicals.**

    1.  Deicing/anti-icing chemicals commonly used on airfields and for
        aircraft degrade rapidly due to chemical and biological
        processes. These processes often cause a large drop in the
        dissolved oxygen levels of receiving waters off the airport. It
        has been suggested that the resultant dissolved oxygen levels
        are too low to support healthy biotic communities occupying
        those water bodies. Although low temperatures and dilution from
        heavy snow runoff during periods of use minimize the effects of
        low dissolved oxygen, and the ammonia from decomposing urea
        quickly dissipates, it is wise to consult with an agency having
        expertise in water quality. This consultation should highlight
        best management practices or best available technology for
        effectively meeting storm water permit conditions established to
        protect the water quality of aquatic life in receiving waters.

    2.  All freezing point depressants can cause scaling of Portland
        cement concrete (PCC) by physical action related to the chemical
        concentration gradient in the pavement. Deleterious effects on
        PCC can be reduced by ensuring sufficient cover over reinforcing
        steel (minimum of 2 inches (5 cm)), using air-entraining
        additives, and avoiding applications of chemicals for one year
        after placement. Concrete meeting the compressive strength
        outlined in ASTM C 672*, Scale Resistance of Concrete Surfaces
        Exposed to Deicing Chemicals*, will perform well when subjected
        to chemical deicers. Certain PCC runways may experience
        excessive alkali-silica reaction that causes accelerated
        deterioration and cracking. Proper selection of aggregates and
        the use of additives can mitigate this occurrence in new PCC
        runways. Coatings for existing PCC runways are being researched
        to determine their effectiveness in mitigating this occurrence.
        No surface degradation of asphalt concrete has been observed
        from approved chemicals.

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7.  []{#__RefHeading___Toc213137138 .anchor}**Runway Friction
    Improvements.** Since snow and ice degrade the coefficient of
    friction between rubber tires and pavement and could pose an unsafe
    condition for aircraft, it is important to clear to bare pavement
    whenever possible. There are situations where complete removal is
    difficult or impossible to achieve within a required span of time;
    at temperatures approaching the *eutectic temperature* of an
    anti-icing/deicing chemical, for instance, it may require an hour or
    more for the chemical to go into solution and melt the ice. There
    are two techniques for modifying the frictional coefficient of a
    pavement covered with ice or compacted snow---one by building in a
    texture on the surface and the other by a surface treatment of the
    ice or snow. It is emphasized that heated sand is not a deicing
    chemical and will not remove ice or compacted snow. In fact, heavy
    applications of heated sand can insulate the ice and therefore
    prolong its presence.

    a.  **Pavement Surface Modification.** Surface texture and surface
        treatment modifications by themselves will not increase the
        coefficient of friction of ice formed on the surface, but both
        will enhance the response of chemical treatment**.**

        1.  **Pavement Grooving.** Grooves cut into the pavement will
            trap anti-icing/deicing chemicals, reduce loss, and prolong
            their actions. Grooves also assist in draining melt water
            and preventing refreezing. There is empirical evidence that
            grooves and porous friction courses modify the thermal
            characteristics of a pavement surface, probably by reducing
            the radiant heat loss, and delay the formation of ice. There
            do not appear to be any negative effects from grooving
            pavements.

        2.  **Porous Friction Course (PFC).** PFC has generally the same
            benefits as grooving. Open graded asphalt concrete is less
            effective in improving coefficient of friction under icing
            conditions because the open spaces will fill with compacted
            snow and, to a lesser extent, with ice in the case of
            freezing rain. Most maintenance personnel have found that
            chemical treatment rates may need to be increased on this
            type of pavement compared to dense graded asphalt concrete
            because of drainage of the chemical. The drainage
            characteristics also change as sand accumulates in the voids
            and plugs them.

    b.  **Surface Treatment.** This is the approach taken to rapidly
        increase the frictional coefficient of an ice surface. Two
        methods are generally used by airport operators, namely applying
        coarse granular material (heated sand) or scarifying or breaking
        up the ice surface with a serrated blade.

        1.  **Sand.** Granular material provides a roughened surface on
            ice and thereby improves airplane directional control and
            braking performance. Use of sand should be controlled
            carefully on turbojet movement areas to reduce engine
            erosion. If the granules do not embed or adhere to the ice,
            they will likely be ingested into engines and/or blown away
            by wind or scattered by traffic action and thus serve no
            useful function. This is particularly the case when unheated
            sand is applied to ice or compacted snow is at temperatures
            below about 20° F (-6.7° C) since no water film exists on
            the surface to act as an adhesive. There are three
            approaches to reducing loss of sand: (1) it can be heated to
            enhance embedding into the cold surface; (2) the granules
            can be coated with an approved deicing chemical in the
            stockpile or in the distributing truck hopper; or (3)
            diluted deicing chemical can be sprayed on the granules or
            the pavement at the time of spreading. If stockpiles are
            kept in a heated enclosure and spread promptly after truck
            loading, sufficient heat may remain for embedding without
            further treatment. Maintenance personnel should make a test
            on an unused pavement covered with ice or compacted snow to
            determine if bonding is adequate to prevent loss. When the
            slippery condition giving rise to the requirement for sand
            has passed, treated pavements should be swept as soon as air
            traffic volume allows to remove the residue to prevent
            engine damage. Other factors to consider when deciding to
            apply sand are pavement and air temperatures and frequency
            of operations. The use of other abrasives, such as slag, is
            not recommended since some metal-based slags may affect
            engine components.

        2.  **Ice Scarifying.** Directional control of vehicles on an
            ice or compacted snow surface can be improved dramatically
            by cutting longitudinal grooves in the ice. However, no
            improvement in braking effectiveness results from grooving,
            so this approach should only be employed when very low
            temperatures prevent rapid chemical action or mechanical
            removal. The grooves trap sand or chemicals and hence
            contribute to improving the surface friction characteristics
            and melting action.

8.  []{#__RefHeading___Toc213137139 .anchor}**Sand.**

    a.  **Material.** All sands do not perform the same. In general, the
        greater the quantity of sand applied, the greater the increase
        in traction. Fine sands show superior performance on warmer ice
        (\>20° F (-7° C)), while coarser sands show superior performance
        on colder ice (\<15° F (-9° C)). For the purpose of this AC,
        sand retained on a #30 sieve is considered "coarse", and sand
        passing through a #30 sieve is considered "fine". The FAA
        recommends that airport operators inform tenant airlines about
        the material used on the runways.

  -----------------------------------------------------------------------
  **Note**: Slag material is not recommended because engine manufacturers
  have reported problems with internal engine components, especially for
  certain types of metal slags.

  -----------------------------------------------------------------------

1.  **Standard Gradation.** Table 4-2 provides the standard gradation
    for sand. Materials applied to aircraft movement surfaces must
    consist of washed granular mineral sand particles free of stone,
    clay, debris, slag, chloride salts, and other corrosive substances.
    The pH of the water solution containing the material must be
    approximately neutral (pH 7). Material must meet the following
    gradation using a U.S.A. Standard Sieve conforming to *ASTM E
    11-81*. The upper and lower sand gradations are in response to
    engine manufacturers input that finer sized sand from time to time
    produced hard snowballs while coarser sized sand damaged engine
    components. The later case additionally causes damage to the
    fuselage.

[]{#__RefHeading___Toc212274681 .anchor}Table 4-2. Standard Gradation
for Sand

  ---------------------------------- ------------------------------------
  Sieve Designation                  Percent by Weight Passing

  8                                  100

  80                                 0-2
  ---------------------------------- ------------------------------------

2.  **Recommended Gradation.** Table 4-3 provides an expanded sand
    gradation standard for optimum performance on both warm and cold ice
    conditions by balancing fine and coarse particles. For this reason,
    the inclusion of the #30 sieve beyond that required by the FAA
    standard gradation of Table 4-2 is recommended. Airport operators
    may modify these recommended gradation requirements to suit their
    needs, as long as the gradation meets the requirements of table 4-2.

[]{#__RefHeading___Toc212274682 .anchor}Table 4-3. Expanded Sand
Gradation Standard

+---------------------------------+------------------------------------+
| ####### Sieve Designation       | ####### Percent by Weight Passing  |
+---------------------------------+------------------------------------+
| 8                               | 100                                |
+---------------------------------+------------------------------------+
| 30                              | 20-50                              |
+---------------------------------+------------------------------------+
| 80                              | 0-2                                |
+---------------------------------+------------------------------------+

b.  **Application.** Hard silica sand provides the greatest increase in
    traction and remains effective the longest when compared to softer
    materials because of its resistance to fracture. However, it is also
    very abrasive and, therefore, more potentially damaging to airplane
    engines. Limestone is softer and may be used where available if
    abrasion needs to be reduced. Tests have shown that application
    rates of 0.02 - 0.10 lb/ft^2^ (0.1 - 0.5 kg/m^2^) of sand will
    substantially increase the runway friction coefficient. The greater
    quantity is required at temperatures approaching 32° F (0° C), the
    amount decreasing as the temperatures drops. Fractured particles
    provide some advantage in traction enhancement but not enough to
    justify much of a difference in cost. In terms of color, darker
    sands are preferred over light-colored sands to offer visual
    verification where sand has been applied.

c.  **Chemically or Heat-treated Sand.** The FAA recommends that sand be
    heated or treated with approved chemicals to make it adhere better
    to ice or compacted snow, thereby minimizing the possibility of
    airplane engine ingestion and preventing loss of material (see 14
    CFR Section 139.313(b)(3).) At temperatures above 15° F (-9° C), a
    solution of airside urea may be used; below this temperature, other
    approved fluids will be more effective. Airport operators report
    that approximately 8 to 10 gallons (30-40 l) of fluid chemical are
    required to coat one ton of sand. The most effective method of
    applying the chemical is to spray it on granules as they drop onto
    the spinner mechanism of a material spreader since wetting is more
    thorough than pouring the chemicals onto the stockpile or the hopper
    load. Below 0° F (-18° C), heated sand can be more effective because
    of more rapid adhesion of the granules to ice. If sand will be
    heated, a coarser mixture (#30 sieve is considered "coarse") should
    be used, as fine particles cool too rapidly on dispersal before
    hitting the ice. Sands heated to 80° F (27° C) or higher adhere well
    to ice.

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# Chapter 5. Runway Surface Assessment and Reporting

[]{#fiveone .anchor}

1.  **Introduction.**

    a.  **Background**. The Snow Control Center (SCC) must be aware of
        the surface conditions of all aircraft movement areas in order
        to plan and carry out appropriate maintenance actions or to
        close a runway, taxiway, or ramp area to aircraft use. Assessing
        and reporting the surface condition of a runway poses a
        particular challenge for an airport operator and is of the
        utmost importance to airport users. Pilot braking action reports
        are the source of braking action information most accepted by
        pilots, but they can vary significantly, even when reporting on
        the same contaminated surface conditions, and obviously only
        apply to the portion of the runway where braking occurred. The
        use of a truck or automobile to estimate airplane braking action
        is also subjective. Research by the FAA at one time indicated
        that measurements using approved friction measuring devices
        would provide pilots with an objective assessment of the braking
        action that could be expected on the runway, but later research
        has not been able to identify a consistent and usable
        correlation between those measurements and airplane braking
        performance. Thus, this advisory circular contains significant
        changes to FAA recommendations regarding reporting of friction
        values.

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    a.  **Providing information to pilots.** The goal in reporting
        runway surface conditions is to provide pilots with the best
        information available to ensure safe operations. Currently,
        there is no objective type of measurement of runway surface
        condition that has been shown to consistently correlate with
        airplane performance in a usable manner to the satisfaction of
        the FAA. Pilots and airplane operators are expected to use all
        available information, which should include runway condition
        reports as well as any available pilot braking action reports,
        to assess whether operations can be safely conducted. Although
        the FAA no longer recommends providing friction measurements to
        pilots for the reasons stated in the paragraph above, some
        airport users still consider runway friction measurement values
        to be useful information for tracking the trend of changing
        runway conditions. Therefore continued transmittal of Mu values
        is permissible with the understanding that the particular
        numerical value has no particular significance other than to
        provide changing runway condition trend information when
        associated with previous or subsequent runway friction
        measurement values. Airport operators are cautioned against
        using Mu values as their sole indicator of winter runway
        slipperiness. Additionally, note the U.S. movement to the use of
        the ICAO term "medium" instead of the term "fair." Until the
        transformation to ICAO terminology is complete, this AC will
        express the term as "medium (fair)."

    b.  **Runway closures.** The previously accepted philosophy of the
        aviation industry was that the airport operator was obligated to
        provide an accurate description of the runway conditions, and it
        was solely up to the pilot to decide if the runway was safe for
        use. Accident data do not support such a philosophy, and FAA
        Flight Standards Service has determined that operations on
        runways reported as having NIL braking are inherently unsafe.
        Admittedly, this is a conservative approach considering the
        variation in pilot braking action reporting, but considering the
        possible consequences of ignoring a NIL braking action report,
        requirements for closure of runways are presented in paragraph
        below.

2.  []{#__RefHeading___Toc213137144 .anchor}**Runway Condition
    Reporting.** The SCC needs to carefully monitor changing airfield
    conditions and disseminate information about those conditions in a
    timely manner to airport users. Part 139 requires affected airport
    operators to issue prompt notification, in accordance with section
    139.313(b), to all air carriers using the airport when any portion
    of the movement area normally available to them is less than
    satisfactorily cleared for safe operation by their aircraft. In
    addition, SICPs must contain provisions for informing all airplane
    operators of any pavement condition that is worse than bare and dry.
    It is imperative that the field condition report contain accurate
    and timely information. For example, the type and depth of
    contaminant is critical information to airplane operators. Also, the
    determination of dry versus wet snow or slush condition is another
    key element in the report because of its potential for significant
    impact on an airplane's takeoff and landing performance
    capabilities.

Because runway surface conditions can change quickly, either due to
weather conditions or corrective actions taken to mitigate such
conditions, NOTAMs describing the runway surface conditions must be
*timely.* The FAA recommends that airport operators review their
reporting method and procedures so their SICP procedures are conducive
to timely reporting. For airports, particularly smaller airports, that
do not monitor weather conditions between certain hours due to staffing
limitations, the issued NOTAM should contain text indicating that
*"airfield surface conditions are not monitored between the hours of 'x
-- y'."* This additional text helps to avoid erroneous condition
assessments by users of the information.

a.  **How to Report Runway Conditions.** Whenever a runway is
    contaminated by ice, snow, slush, or standing water, the airport
    operator is responsible for providing current runway surface
    condition reports. Report runway surface conditions in terms of
    contaminant types and depths (except do not report depths for
    compacted snow and ice, and for standing water or slush depths less
    than 1/8 inch). When the cleared runway width is less than the full
    runway width, also report the conditions on the uncleared width
    (runway edges) if different from the cleared width.

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b.  **When to Issue New Runway Condition Reports.** Runway condition
    reports must be updated any time a change to the runway surface
    condition occurs. Changes that initiate updated reports include
    weather events, the application of chemicals or sand, or plowing or
    sweeping operations. Airport operators should not allow airplane
    operations on runways after such activities until a new runway
    condition report is issued reflecting the current surface
    condition(s) of affected runways. At certificated airports, such
    changes to the runway surface condition must be updated and
    appropriately disseminated so airplane operators are aware of the
    current conditions before continuing with their operations. During
    active snow events or rapidly changing conditions (e.g., increasing
    snowfall, rapidly raising or falling temperatures) airport operators
    are required to maintain a vigilant runway inspection process to
    ensure accurate runway condition reports. While pilot reports
    (PIREPs) of braking action provide valuable information, these
    reports may not apply to the full length of the runway as such
    evaluations are limited to the specific sections of the runway
    surface in which the airplane wheel braking was used. In addition,
    runway condition reports should be updated at least at the beginning
    of each shift of operations personnel.

c.  **Airport Records and Log Controls.** The SICP should include
    procedures to keep and maintain a log of NOTAMs that the airport
    operator issues. Reviewing NOTAM status should be a checklist item
    anytime the runway condition changes from that previously contained
    in the NOTAM and at the change of each shift of airport operations
    personnel. Also, retain a copy of the NOTAM as submitted and as
    transmitted for future reference and to demonstrate regulatory
    compliance when applicable.

d.  **Winter NOTAM Abbreviations.** Snow-related NOTAMs should adhere to
    the format and abbreviations found in AC 150/5200-28, *Notices to
    Airmen (NOTAMs) for Airport Operators,* and FAA Orders 7930.2,
    *Notices to Airmen (NOTAMS),* and 7340.1, *Contractions.*

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3.  []{#__RefHeading___Toc213137145 .anchor}**Runway Friction Surveys.**
    FAA-approved friction measuring equipment may be employed to help in
    determining the effects of friction-enhancing treatments, in that it
    can show the trend of a runway as to increasing or decreasing
    friction. Airport operators must not attempt to correlate friction
    readings (Mu numbers) to Good/Medium (Fair)/Poor or Nil runway
    surface conditions, as no consistent, usable correlation between Mu
    values and these terms has been shown to exist to the FAA's
    satisfaction. It is important to note that while manufacturers of
    the approved friction measuring equipment may provide a table that
    correlates braking action to Mu values, these correlations are not
    supported by the FAA. To ensure that data collected are accurate,
    qualified personnel should use FAA-approved equipment and follow the
    manufacturer's instructions for use. Further guidance on runway
    friction measurement may be found in AC 150/5320‑12C, *Measurement,
    Construction, and Maintenance of Skid-Resistant Airport Pavement
    Surfaces*.

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a.  **Conditions Acceptable to Use Decelerometers or Continuous Friction
    Measuring Equipment to Conduct Runway Friction Surveys on Frozen
    Contaminated Surfaces.** The data obtained from such runway friction
    surveys are only considered to be reliable when the surface is
    contaminated under any of the following conditions.

    1.  Ice or wet ice. Wet ice is a term used to define ice surfaces
        that are covered with a thin film of moisture caused by melting.
        The liquid water film deposit is of minimal depth of 0.04 inch
        (1 mm) or less, insufficient to cause hydroplaning.

    2.  Compacted snow at any depth.

    3.  Dry snow 1 inch or less.

    4.  Wet snow or slush 1/8 inch or less.

It is not acceptable to use decelerometers or continuous friction
measuring equipment to assess any contaminants outside of these
parameters.

a.  **When to Conduct Runway Friction Assessments on Contaminated
    Surfaces.** The airport operator should conduct runway friction
    assessments whenever it is thought that the information will be
    helpful in the overall snow/ice removal effort, and the conditions
    are within the limits above. Within those conditions, runway
    friction assessments should be conducted:

    1.  When the central portion of the runway, centered longitudinally
        along the runway centerline, is contaminated over a distance of
        500 feet (152 m) or more.

    2.  Following all snow clearing, anti-icing, deicing, or sanding
        operations.

    3.  Immediately following any aircraft incident or accident on the
        runway, recognizing that responding ARFF or other circumstances
        may restrict an immediate response.

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4.  []{#__RefHeading___Toc213137146 .anchor}**FAA-Approved Runway
    Friction Measuring Equipment.** There are two basic types of
    friction measuring equipment that can be used for conducting
    friction surveys on runways during winter operations: Continuous
    Friction Measuring Equipment (CFME) and Decelerometers (DEC).

    a.  **Continuous Friction Measuring Equipment (CFME).** CFME devices
        are recommended for measuring friction characteristics of
        pavement surfaces covered with contaminants, as they provide a
        continuous graphic record of the pavement surface friction
        characteristics with friction averages for each one-third zone
        of the runway length. They may be either self-contained or
        towed. AC 150/5320-12, *Measurement, Construction, and
        Maintenance of Skid-Resistant Airport Pavement Surfaces*,
        contains performance specifications for CFME in Appendix 3 and a
        list of FAA-approved equipment in Appendix 4.

    b.  **Decelerometers.** Decelerometers are recommended for airports
        where the longer runway downtime required to complete a friction
        survey is acceptable, and may actually be preferred at some busy
        airports where it is difficult to gain access to the full length
        of a runway crossed by another runway. Decelerometers should be
        of the electronic type due to the advantages noted below.
        Mechanical decelerometers may be used, but should be reserved as
        a backup. Airports having only mechanical devices should plan to
        upgrade as soon as possible. Neither type of decelerometer will
        provide a continuous graphic record of friction for the pavement
        surface condition. They provide only a spot check of the
        pavement surface. On pavements with patches of frozen
        contaminants, decelerometers may be used only on the
        contaminated areas. For this reason, a survey taken under such
        conditions will result in a conservative representation of
        runway braking conditions. This should be considered when using
        friction values as an input into decisions about runway
        treatments. In addition, any time a pilot may experience widely
        varying braking on various portions of the runway, it is
        essential that the patchy conditions be noted in any report
        intended to relay friction values to pilots. FAA-approved
        decelerometers are listed in Appendix 3 of this AC, and
        performance specifications are provided in Appendix 4.

        1.  **Electronic Decelerometers.** Electronic decelerometers
            eliminate potential human error by automatically computing
            and recording friction averages for each one-third zone of
            the runway. They also provide a printed record of the
            friction survey data.

        2.  **Mechanical Decelerometers.** Mechanical decelerometers may
            be used as a backup to an electronic decelerometer. The
            runway downtime required to complete a friction survey will
            be longer than with an electronic decelerometer. Mechanical
            decelerometers do not provide automatic friction averages or
            a printed copy of data.

    c.  **Friction Measuring Procedures.**

        1.  **Calibration.** The friction measuring equipment operator
            is responsible for ensuring that equipment is correctly
            calibrated in accordance with its operations manual. Some
            devices perform an automatic electronic calibration each
            time the power is turned on; others require the operator to
            initiate the calibration procedure. In the latter case, the
            electronic calibration should be performed before placing
            the equipment in operation for the day. The equipment
            operator should also check all ancillary systems (such as
            recording devices, tow vehicles, and two-way radios).
            Factory calibrations of CFME should be performed as
            recommended by the manufacturer, or sooner if indicated by
            erroneous data. The operator responsible for the device
            should perform only adjustments recommended by the
            manufacturer. Factory calibration should be scheduled during
            the spring-summer season to ensure the equipment will be
            ready for the next winter's runway friction surveys.

        2.  **Advance Coordination.** Runway friction surveys take time,
            and while the tests are being conducted, the runway may be
            closed to air traffic. Airport operators should work closely
            with ATC, the airlines, and/or the fixed-base operators to
            minimize interruption to airplane operations. Close
            coordination, communication, and cooperation among all
            parties concerned are vital to ensure personnel safety,
            efficient traffic management, and timely runway friction
            surveys. The airport operator should request from ATC an
            appropriate period of time to conduct a friction survey of
            the runway. At a high-activity airport, runway friction
            surveys may have to be conducted in segments. The airport
            operator should request ATC to plan a break in arrival and
            departure traffic to provide time to conduct a runway
            friction survey. With such planning, the friction survey
            team can position itself adjacent to the runway when ATC
            gives the clearance to proceed. This cooperative effort with
            ATC will result in minimal disruptions to airplane
            operations. A letter of agreement between the airport
            operator and ATC can be used to identify the procedures and
            responsibilities for coordination and for reporting runway
            surface conditions.

        3.  **Air Traffic Control Clearance When Conducting Runway
            Friction Surveys on Open Runways.** Before proceeding with
            the friction survey at controlled airports, the airport
            operator responsible for conducting the friction survey must
            contact ATC for runway clearance according to standard
            procedures and remain in radio contact during the entire
            time it takes to complete the friction survey on an open
            runway. ATC will provide appropriate clearances on and off
            the runway to permit the airport operator access to conduct
            the friction survey. At uncontrolled airports, airport
            operations personnel must be alert for aircraft and advise
            any air traffic on advisory frequencies before, during, and
            after completion of the runway friction survey. In this
            situation, coordination among the area ATC, the airport
            operator, and the airplane operators is particularly
            important to ensure that safe and efficient airplane
            operations are maintained at all times.

        4.  **Location and Direction to Conduct Runway Friction
            Surveys.**

            i.  **Lateral Location.** On runways that serve primarily
                narrow-body airplanes, runway friction surveys should be
                conducted approximately 10 feet (3 m) from the runway
                centerline. On runways that serve primarily wide-body
                airplanes, runway friction surveys should be conducted
                approximately 20 feet (6 m) from the runway centerline.
                Unless surface conditions are noticeably different on
                the two sides of the runway centerline, only one survey
                is needed, and it may be conducted on either side.

            ii. **Direction.** Friction measuring equipment is operated
                in the same direction that airplanes are landing.

            iii. **Runway Survey Zones.** The runway length is divided
                 into three equal zones: the touchdown, midpoint, and
                 rollout zones. These zones are defined according to
                 airplane landing direction. If possible, the entire
                 survey should be completed in one pass. However, if ATC
                 cannot schedule enough time to do a complete runway
                 friction survey, the airport operator should request
                 ATC to schedule each zone separately until all three
                 zones have been completed.

        5.  **Conducting Runway Friction Surveys Using Decelerometers.**
            A minimum of three braking tests are required in each zone
            to determine the average friction value for that zone. This
            will result in a minimum of nine tests for a complete runway
            friction survey. The vehicle speed for conducting the
            friction survey should be 20 mph (32 km/h). Example #1
            provides an illustration.

+-----------------+-----------------------------------------------------+
| ***Example      |                                                     |
| #1***           |                                                     |
+-----------------+-----------------------------------------------------+
| *Runway Zone 1* | *A qualified airport operator obtains four Mu       |
|                 | readings in the touchdown zone: 25, 27, 26, and 31. |
| *Touchdown*     | The average of these readings is 27.25, which would |
|                 | be rounded to 27.*                                  |
+-----------------+-----------------------------------------------------+
| *Runway Zone 2* | *Four readings are obtained for the midpoint zone:  |
|                 | 26, 28, 28, and 32. The average of 28.5, which      |
| *Midpoint*      | would be rounded to 29**.***                        |
+-----------------+-----------------------------------------------------+
| *Runway Zone 3* | *After the minimum three readings (29, 30, and 31)  |
|                 | are obtained for the rollout zone, ATC instructs    |
| *Rollout*       | the operator to clear the runway. It is not         |
|                 | required that an equal number of readings be        |
|                 | obtained for each zone, so the three readings are   |
|                 | averaged to a reading of **30**.*                   |
+-----------------+-----------------------------------------------------+

6.  **Conducting Runway Friction Surveys Using CFME.** A runway friction
    survey is recommended for the full length of the runway to determine
    the average friction value for each zone. The survey may be
    conducted at any speed up to 40 mph (65 km/h) as safety
    considerations allow. Some CFME should be operated at slower speeds
    due to handling characteristics that are a function of their weight,
    measuring method, etc. Operators should be trained in the use of
    CMFE, and such training should include information on handling
    characteristics and optimum testing speeds.

7.  **Recording Runway Friction Survey Data.** The equipment operator
    should record all data and observations obtained from runway
    friction surveys. Recorded data and observations can be used to
    assess the effectiveness of runway surface treatments and snow
    removal operations and can aid in accident or incident
    investigations. Table 5-1 provides a recommended format for
    recording this data. The remarks column can be used to record pilot
    braking action reports and associated airplane type as well as other
    observations of any unusual conditions that existed when the runway
    friction surveys were conducted. CFME and electronic decelerometers
    provide the airport operator with their own records. These records
    may be used in lieu of the suggested form, as appropriate.

[]{#fivefour .anchor}

5.  **Friction Assessment Reporting.**

    a.  **When to Report Friction Values.** Friction values may be
        reported to interested parties under the following conditions:

        1.  When compacted snow and/or ice are present on the center
            portion of the runway, and friction values are **40 or
            below** on any zone of the runway.

  -----------------------------------------------------------------------
  **Note 1:** Current friction measurement technologies are not reliable
  in determining braking effectiveness of a contaminated surface
  condition above measurements of 40. Therefore, 40 is the highest value
  for reporting friction measurements on contaminated surfaces. For
  example, in a case where friction values for the three runway zones are
  27, 35, and 42, the reported values would be 27, 35, 40+ (or "above
  40").

  -----------------------------------------------------------------------

2.  When friction values rise above 40 on all zones of any active runway
    previously showing a friction below 40. The reported value in all
    cases is above 40 per Note 1.

  -----------------------------------------------------------------------
  **Note 2:** Friction values are technically decimal numbers (e.g.,
  0.10, 0.24, 0.30) but are generally referred to using whole numbers
  (10, 24, 30) for convenience. Confusion between the decimal and whole
  numbers is rarely a problem.

  -----------------------------------------------------------------------

b.  **Friction Condition** **Report Contents.** The friction condition
    report should identify the friction tester type and the runway
    number, followed by the average friction numbers for each of the
    three runway zones (rounded to the nearest whole number), a short
    description of the type of contamination causing the runway friction
    problem, and the time the report was taken. It is especially
    important that pilots be advised of patchy conditions that may
    result in different braking action on various sections of the
    runway. Example #2 provides an illustration.

+-----------------------------------------------------------------------+
| ***Example #2***                                                      |
|                                                                       |
| A qualified airport operator conducts a survey on Runway 14R with an  |
| FAA-approved CFME and obtains averages for the touchdown, midpoint,   |
| and rollout sections of 23, 27, and 32, respectively. The operator    |
| notes the surface is contaminated by compacted snow, with patches of  |
| ice. The survey is completed at 10:15 AM.                             |
|                                                                       |
| The report transmitted to ATC would include the following: Name of    |
| the FAA-approved friction tester, average friction values for Runway  |
| 14R of 23, 27, 32, compacted snow with patchy ice at one zero one     |
| five. Information is transmitted by NOTAM.                            |
+-----------------------------------------------------------------------+

c.  **Procedures for Reporting Friction Information to the Airport
    Traffic Control Tower (ATCT).** The procedure for transmitting
    friction values to ATC for dissemination to pilots may vary from
    airport to airport. Any letter of agreement between the airport
    operator and ATCT should spell out the procedures for each type of
    event--- runway closure, friction survey results, runway treatment,
    etc. For example, certain friction equipment manufacturers offer the
    airport operator an optional data link system that provides direct
    transmission of the friction measuring equipment data to the airport
    operator, ATCT, airline stations, and other airport users. Reports
    may also be furnished to local operators, airlines, or other users.
    In the absence of a control tower at the airport, the report should
    be supplied to the ATC facility that provides approach control
    service or to an appropriate flight station, fixed-base operator,
    scheduled service airlines operating at the airport, or other
    authority to broadcast on the Unicom, Common Traffic Advisory
    Frequency, or Airport Advisory Service Frequency.

d.  **Out-of-Service Friction Measuring Equipment.** During winter
    operations, if friction values taken on compacted snow and/or ice
    have been issued on a regular basis and the equipment used to obtain
    these values is not available, a NOTAM should be issued and
    maintained until the equipment is restored to service.

```{=html}
<!-- -->
```
6.  []{#__RefHeading___Toc213137148 .anchor}**Requirements For Runway
    Closures.** The following circumstances require the prescribed
    action by the airport operator:

    a.  A NIL pilot braking action report (PIREP), or NIL braking action
        assessment by the airport operator, requires that the runway be
        closed before the next flight operation. The runway must remain
        closed until the airport operator is satisfied that the NIL
        condition no longer exists.

    b.  When previous PIREPs have indicated GOOD or MEDIUM (FAIR)
        braking action, two consecutive POOR PIREPS should be taken as
        evidence that surface conditions may be deteriorating and
        require the airport operator to conduct a runway assessment. If
        the airport operator has not already instituted its continuous
        monitoring procedures (see paragraph 5-7), this assessment must
        occur before the next operation. If the airport operator is
        already continuously monitoring runway conditions, this
        assessment must occur as soon as air traffic volume allows, in
        accordance with their SICP. Deteriorating conditions include but
        are not limited to:

        -   Frozen or freezing precipitation

        -   Falling air or pavement temperatures that may cause a wet
            runway to freeze

        -   Rising air or pavement temperatures that may cause frozen
            contaminants to melt

        -   Removal of abrasives previously applied to the runway due to
            wind or airplane affects

        -   Frozen contaminants blown onto the runway by wind

    c.  Under the conditions noted above, the airport operator must take
        all reasonable steps using all available equipment and materials
        that are appropriate for the condition to improve the braking
        action. If the runway cannot be improved, the airport operator
        must continuously monitor the runway to ensure braking action
        does not become NIL. The airport operator's procedure for
        monitoring the runway should be detailed in the SICP.

    d.  To ensure that the airport operator receives needed information,
        a Letter of Agreement (LOA) should be formalized between the
        airport operator and the air traffic control tower. At a
        minimum, the LOA should specify how all pilot braking reports
        (PIREPS) of "POOR" and "NIL" are to be immediately transmitted
        to the airport operator, e.g., the SCC for action, as required
        by FAA Order 7110.65, *Air Traffic Control*. It should also
        include agreement on actions by Air Traffic personnel for
        immediate cessation of operations upon receipt of a "NIL" PIREP.
        A reference to the signed LOA, whose procedures for ATCT and the
        airport will likely vary from airport to airport, should be
        contained in the airport's SICP. Finally, the airport operator
        must inform airport users in a timely manner of any runway
        closure. See paragraph 5-2, Runway Condition Reporting, for
        disseminating such information in a timely manner to airport
        users.

7.  []{#__RefHeading___Toc213137149 .anchor}**Continuous Monitoring.**
    "Continuous monitoring" procedures can vary from airport to airport.
    Acceptable procedures may include:

-   Observing which exit taxiways are being used.

-   Maintaining a regular program of friction testing to identify trends
    in runway traction.

-   Monitoring runway physical conditions including air and surface
    temperatures, contaminant types and depths.

-   Monitoring pilot communications.

-   Monitoring weather patterns.

[]{#__RefHeading___Toc212274684 .anchor}Table 5-1. Runway Contamination
Mitigation Record (top) and Runway Friction Survey Record (bottom)

+----+-----+--------+-----------------------+--------+-----+-----+----+
| ** | *   | *      | ***DESCRIPTION OF     | *      |     | **  |    |
| *D | **T | **RUNW | SURFACE               | **TYPE |     | *TE |    |
| AT | IME | AY-*** | CONDITION(S)***       | OF     |     | MPE |    |
| E* | *** |        |                       | CONTA  |     | RAT |    |
| ** |     | *      |                       | MINANT |     | URE |    |
|    |     | **TAXI |                       | REMO   |     | *** |    |
| ** |     | WAY*** |                       | VED*** |     |     |    |
| *O |     |        |                       |        |     |     |    |
| F* |     | ***D   |                       |        |     |     |    |
| ** |     | ESIGNA |                       |        |     |     |    |
|    |     | TOR*** |                       |        |     |     |    |
| ** |     |        |                       |        |     |     |    |
| *S |     |        |                       |        |     |     |    |
| UR |     |        |                       |        |     |     |    |
| VE |     |        |                       |        |     |     |    |
| Y* |     |        |                       |        |     |     |    |
| ** |     |        |                       |        |     |     |    |
+----+-----+--------+-----------------------+--------+-----+-----+----+
|    |     |        |                       | ***MET | *   | *   | *  |
|    |     |        |                       | HOD(S) | **T | **A | ** |
|    |     |        |                       | EMPLO  | IME | MBI | PA |
|    |     |        |                       | YED*** | *** | ENT | VE |
|    |     |        |                       |        |     | *** | -M |
|    |     |        |                       |        |     |     | EN |
|    |     |        |                       |        |     |     | T* |
|    |     |        |                       |        |     |     | ** |
+----+-----+--------+-----------------------+--------+-----+-----+----+
|    |     |        |                       |        |     |     |    |
+----+-----+--------+-----------------------+--------+-----+-----+----+
|    |     |        |                       |        |     |     |    |
+----+-----+--------+-----------------------+--------+-----+-----+----+
|    |     |        |                       |        |     |     |    |
+----+-----+--------+-----------------------+--------+-----+-----+----+
|    |     |        |                       |        |     |     |    |
+----+-----+--------+-----------------------+--------+-----+-----+----+
|    |     |        |                       |        |     |     |    |
+----+-----+--------+-----------------------+--------+-----+-----+----+

+-------+------+----+--------+------+-----+-----+-----------------+
| **    | **   | *  | ***LO  | ***  |     |     | ***REMARKS***   |
| *TYPE | *DAT | ** | CATION | AVER |     |     |                 |
| OF    | E*** | VE | OF     | AGED |     |     |                 |
| FRI   |      | HI | TEST   | Mu   |     |     |                 |
| CTION | ***O | CL | RUN    | REA  |     |     |                 |
| MEAS  | F*** | E* | FROM   | DING |     |     |                 |
| URING |      | ** | RUNWAY | BY   |     |     |                 |
| D     | ***L |    | C      | ZON  |     |     |                 |
| EVICE | AST\ | *  | ENTERL | E*** |     |     |                 |
| US    | CA   | ** | INE*** |      |     |     |                 |
| ED*** | LIBR | SP |        |      |     |     |                 |
|       | ATIO | EE | ***(FE |      |     |     |                 |
|       | N*** | D* | ET)*** |      |     |     |                 |
|       |      | ** |        |      |     |     |                 |
|       |      |    |        |      |     |     |                 |
|       |      | *  |        |      |     |     |                 |
|       |      | ** |        |      |     |     |                 |
|       |      | (M |        |      |     |     |                 |
|       |      | PH |        |      |     |     |                 |
|       |      | )* |        |      |     |     |                 |
|       |      | ** |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        | ***  | **  | *   |                 |
|       |      |    |        | TOUC | *MI | **R |                 |
|       |      |    |        | HDOW | DPO | OLL |                 |
|       |      |    |        | N*** | INT | OUT |                 |
|       |      |    |        |      | *** | *** |                 |
|       |      |    |        | **   |     |     |                 |
|       |      |    |        | *ZON | *   | *   |                 |
|       |      |    |        | E*** | **Z | **Z |                 |
|       |      |    |        |      | ONE | ONE |                 |
|       |      |    |        |      | *** | *** |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+
|       |      |    |        |      |     |     |                 |
+-------+------+----+--------+------+-----+-----+-----------------+

#  {#section-3 .unnumbered}

# APPENDIX 1. Development of Recommended Snow Bank Height Profiles 

Graphs A2-1 and A2-2 were used to develop the recommended snow bank
profile limits for Figure 4-1. Location and height above a horizontal
reference line of airplane wingtips and outer and inner engine nacelles'
lower edges with airplane outer main gear on the pavement edge
determined individual profiles. These individual profiles were then
grouped according to airplane design groups to generate the
recommendations.

> ![](media/image12.wmf){width="9.17361111111111in"
> height="6.132638888888889in"}
>
> []{#__RefHeading___Toc212272474 .anchor}Graph A1-1. Individual height
> profiles of airplane wingtips and outer and inner engine nacelles'
> lower edges for Airplane Design Groups III and IV

![](media/image13.wmf){width="8.970833333333333in"
height="6.124305555555556in"}

> []{#__RefHeading___Toc212272475 .anchor}Graph A1-2. Individual height
> profiles of airplane wingtips and outer and inner engine nacelles'
> lower edges for Airplane Design Groups V and VI (\* indicates
> preliminary data)

Page intentionally blank

# APPENDIX 2. Snow and Ice Control as a Materials-Handling Problem

[]{#__RefHeading___Toc213137152 .anchor}**A2-1. Introduction.** Snow and
ice have many unique properties that distinguish them from other
materials commonly handled by mechanized mobile equipment. Earthmoving
equipment, for example, is generally not well-adapted to handling snow
because the properties of snow are so different from earth and other
minerals for which this equipment was designed. Typical of these
properties is the unique density, hardness, thermal instability,
cohesiveness, and metamorphism (age hardening) of snow under varying
winter conditions.

[]{#__RefHeading___Toc213137153 .anchor}**A2-2. Snow.** Snow is a
porous, permeable aggregate of ice grains that can be predominantly
single crystals or a close grouping of several crystals. The pores of
cold, dry snow are filled with air and water vapor. In wet snow, the
grains are coated with liquid water.

**a. Density.** This is the weight per unit volume, a measure of how
much material there is in a given volume. Values range from a very low 3
lb/ft ^3^(48 kg/m^3^) for low density, new snow to about 37 lb/ft^3^
(593 kg/m^3^) for older snow. Old snow that has not been compacted by
vehicles or other loads normally will not exceed a density of 25
lb/ft^3^ (400 kg/m^3^). When density exceeds 50 lb/ft^3^ (801 kg/m^3^),
the air passages become discontinuous and the material becomes
impermeable; by convention, it is called ice. Uncompacted snow has
little bearing capacity, so wheels readily sink into it and encounter
rolling resistance. Snow increases in density either by deformation,
such as trafficking, or by a natural aging process (see Paragraph A2-2e
below). Density is measured by weighing a sample of known volume. Though
earth will compact to some extent, its density on handling will increase
only a few percent. In contrast, snow will easily increase in density
over 80 percent during plowing or trafficking.

**b. Hardness.** Hardness or strength depends on the grain structure and
temperature. Grain structure, in turn, is dependent on the density of
the snow and the degree of bonding between adjacent grains. Snow when it
first falls is cohesionless---i.e., individual grains do not stick to
one another---but bonds quickly, forming and growing at grain contacts.
As the temperature of the snow approaches the melting point, 32° F (0°
C), liquid water begins to coat the snow grains. Although density
remains the same, the strength will decrease. Conversely, the strength
or hardness will increase as the temperature drops**.** Hard snow is
difficult to penetrate with a bucket or a blade plow or to disaggregate
with a rotary plow. Typical values for unconfined compressive strength
of well-bonded snow range from less than 1 lbf/in^2^ (6.89 kPa) for new
snow with a density of 6.2 lb/ft^3^ (100 kg/m^3^) to 30 lbf/in^2^ (207
kPa) for well-bonded snow with a density of 25 lb/ft^3^ (400 kg/m^3^).
Hardness is sometimes determined by measuring the resistance to
penetration. However, since a very good correlation exists between
compressive strength and density for cold snow, determination of the
density might suffice to indicate the snow hardness. In contrast, the
strength of dry, frozen ground is little different from thawed ground.
It is only when soil contains water that the strength increases upon
freezing; and depending upon the ice content, it will be much like hard,
compacted snow or ice in its strength.

**c. Thermal Instability.** Snow exists at temperatures relatively close
to its melting point. Most snow properties are dependent on the
temperature. Strength, for example, will decrease rapidly when the
temperature approaches 32° F (0° C) and will increase, though at a
slower rate, as the temperature is lowered. The thermal instability of
snow is particularly important in the case of metamorphism (see
Paragraph A2-2e below).

**d. Cohesiveness.** Individual snow grains will bond to one another to
form a consolidated mass. Although cold, dry snow when initially
deposited will lack cohesion, the age hardening process will quickly
lead to bond formation and increasing cohesion (see Paragraph A2-2e
below). Fine particles of snow produced by a rotary snowplow will adhere
to each other on contact and tend to clog cutting and blowing equipment.

**e. Metamorphism.** Metamorphism is also called age hardening. The
structure of a snow mass is continually changing by migration of water
vapor from small to large grains. The number and extent of grain bonds
increases with time even in an uncompacted mass, and, as a consequence,
the density and the strength increase. The rate of change is increased
when a natural snow cover is disturbed by wind drifting or by mechanical
agitation, such as plowing; in either case, the snow is broken into
smaller fragments, increasing the surface area and the potential for a
greater number of grain contacts. The increase in strength or hardness
can be very rapid following plowing, particularly after blowing with a
rotary snowplow. Only 2 or 3 hours after plowing, snow may require three
times the amount of work to reprocess it. For this reason, it is
advisable to clear snow to its final location as promptly as possible in
order to minimize the amount of work involved.

[]{#__RefHeading___Toc213137154 .anchor}**A2-3. Ice.** Ordinary ice is a
solid form of water consisting of a characteristic hexagonal symmetry of
the water molecules. Its strength and slipperiness distinguish it from
snow both in the action of rubber tires trafficking on ice-covered
pavement and in the effort involved in its removal.

**a.** **Methods of Formation.** There are four common methods by which
ice will form on a surface: (1) radiation cooling, (2) freezing of cold
rain, (3) freeze-thaw of compacted snow, and (4) freezing of ponded or
melt water.

**(1)** **Radiation Cooling.** Any body will radiate energy to another
body having a lower temperature. Pavement exposed to the night sky will
radiate energy to that nearly perfect blackbody, and if the heat is not
replaced as rapidly as it is lost, cooling will result. Pavement
temperature can drop below freezing even when the air temperature is
above freezing. Water vapor in the air deposits on the cold surface and
freezes; the rate and quantity depend on the amount of moisture in the
air and the rate at which the heat of condensation and fusion of the
water vapor are dissipated. The ice forms in discrete particles and may
not cover the pavement completely. Bonding is generally not very strong
since particle contact area is small even when the pavement is
completely covered, and therefore removal is not difficult. A term
applied to this type of ice is surface hoar, or more commonly
"hoarfrost." On occasion, dew will form and then freeze; because of its
greater area of contact, bonding will be very strong. Since the layer of
ice so formed will be very thin and nearly invisible, it is sometimes
called "black ice." Clouds or fog will usually prevent cooling of
pavement by outgoing radiation.

**(2) Freezing of Cold Rain.** Freezing rain is one of the most common
methods of ice formation and one of the most difficult to remove. If the
pavement is at or below 32° F (0° C), rain falling on it can freeze,
depending on a number of factors. Conditions favoring formation of
so-called glare ice or glaze, a homogeneous clear ice cover, are a slow
rate of freezing, large droplet size, high precipitation rate, and no
more than a slight degree of supercooling. The rain has an opportunity
to flow over the surface before freezing, forming a smooth, tightly
bonded cover. Glaze usually forms at air temperatures between 27° F and
32° F (-3° C to 0° C), though some cases have been reported as low as
-5° F (-20° C) or as high as 37° F (3° C). Because of its intimate
contact with the pavement, glaze ice is difficult to remove by
mechanical means.

**(3) Freeze-thaw of Compacted Snow.** At low temperatures compaction of
cold dry snow by passage of wheels will not cause a strong bond to
develop between snow and pavement. However, if the snow has a high water
content or some melting takes place and the temperature subsequently
drops, a bond as strong as that of glaze ice can develop.

**(4) Freezing of Ponded or Melt Water.** These are commonly called
icings (or "glaciers" in some regions). Though the term was originally
limited to ice formed from groundwater flowing onto a pavement, by
extension it applies to water from any source other than directly from
rain. Thus, melt water resulting from poor drainage or water impounded
by snow windrows can cause icings. This type of ice is usually well
bonded to the pavement and, in addition, its thickness may exceed that
of the other types described above. This is the easiest kind of ice to
avoid; proper maintenance practices will prevent accumulation of water
leading to icings.

**b.** **Adhesion to Surfaces.** The bond between ice and pavement when
it is well developed will exceed the tensile strength of ice; and,
therefore, when mechanical removal is attempted, failure will occur
either within the ice or in the pavement itself.

**c. Density.** Bubble-free ice has a density of 57 lb/ft^3^ (914
kg/m^3^), though by convention compacted snow that has become
impermeable (there are no connected air passages) is called ice. This
occurs at a density of about 50 lb/ft^3^ (801 kg/m^3^). Ice arising from
compacted snow will not ordinarily densify beyond this value.

**d.** **Strength.** Ultimate strengths of ice at 23° F (-5° C) are as
follows:

> Tension 15 kgf/cm^2^ 210 lbf/in^2^
>
> Compression 36 500
>
> Shear 7 100
>
> Flexure (bending) 17 240

Ice in the vicinity of the melting point has even lower flexural
rigidity and, therefore, will not be fractured when a tire rolls over an
ice-covered pavement. Ice becomes brittle with increasing rigidity at
low temperatures (below 20° F (-6.7° C)). The bond strength also
increases as the temperature decreases.

[]{#__RefHeading___Toc213137155 .anchor}**A2-4. Slush.** Wet snow has
liquid water coating the grains. Wet snow is easily deformed since the
grains are lubricated and slide easily past one another. If the deposit
is freely drained, no excess water beyond that wetting the surface of
each grain will be present. If, however, the snow lies on an impermeable
surface, such as a pavement, water may not drain freely from it. When
the amount of excess water reaches about 15 percent (i.e., the amount in
excess of the freely drained state) a viscous state is reached and the
mass will splash and flow like a thick liquid. Upon impacting a surface,
such as the landing gear or underside of an airplane, the excess water
will drain, and the snow will compact and frequently bond to the
surface. Slush on a runway is a hazard because it---

**(1)** Greatly increases drag during the takeoff roll.

**(2)** Greatly reduces directional control.

**(3)** Decreases braking effectiveness. Slush can be removed by use of
displacement plows, which are preferably fitted with rubber or polymer
cutting edges (see Paragraph 4-2).

# APPENDIX 3. FAA-Approved Decelerometers\*

+---------------------------------+------------------------------------+
| **BOWMONK USA Distributor\      | **BOWMONK DECELEROMETER\           |
| **Sherwin Industries, Inc\      | **(414) 281-6400\                  |
| 2129 West Morgan Avenue\        | FAX (414) 281-6404\                |
| Milwaukee, WI 53221             | email:                             |
|                                 | <runway@sherwinindustries.com>     |
+---------------------------------+------------------------------------+
| **TAPLEY SALES (CANADA)\        | **TAPLEY DECELEROMETER\            |
| **241 Norseman Street\          | **(416) 231-9216\                  |
| Toronto, Ontario\               | FAX (416) 231-9121                 |
| CANADA M8Z 2R5                  |                                    |
+---------------------------------+------------------------------------+
| **TES INSTRUMENTS\              | **TES ERD MK3 DECELEROMETER\       |
| **1 Stafford Road East\         | **(613) 832-2687\                  |
| Suite 303\                      | FAX (613) 832-2721                 |
| Ottawa, Ontario\                |                                    |
| CANADA K2H 1B9                  |                                    |
+---------------------------------+------------------------------------+
| **VERICOM COMPUTERS, INC.\      | **VERICOM VC3000 RFM               |
| **14320 James Road\             | DECELEROMETER\                     |
| Suite 200\                      | **(800) 533-5547\                  |
| Rogers, MN 55374                | FAX (763) 428-4856                 |
+---------------------------------+------------------------------------+
| **NEUBERT AERO CORP.**          | **NAC DYNAMIC FRICTION**           |
|                                 |                                    |
| 14141 46^th^ Street North       | **DECELEROMETER (DFD)**            |
|                                 |                                    |
| Suite 1206                      | \(727\) 538-8744                   |
|                                 |                                    |
| Clearwater, FL 33762            | FAX (727) 538 8765                 |
|                                 |                                    |
|                                 | Email: info@airportnac.com         |
+---------------------------------+------------------------------------+

# 

\* See Advisory Circular 150/5320-12, *Measurement, Construction, and
Maintenance of Skid-Resistant Airport Pavement Surfaces*, for approved
Continuous Friction Measuring Equipment (CFME).

Page intentionally blank

**APPENDIX 4. Performance Specification for Decelerometers**

[]{#__RefHeading___Toc213137157 .anchor}**A4-1. Scope.** This Appendix
describes the procedures for establishing the reliability, performance,
and consistency of decelerometers.

[]{#__RefHeading___Toc213137158 .anchor}**A4-2. Certification
(General).** The manufacturer will certify electronic or mechanical
decelerometers are---

**a.** Portable, rugged, and reliable.

**b.** Capable of being fitted to vehicles qualified by the requirements
given in this specification. Minimal vehicle modifications will be
necessary to accommodate the mounting plates and electrical connections.
Vehicles are qualified according to their size, braking and suspension
system, shock absorber capabilities, and tire performance. The vehicles
must have the following properties:

**(1)** Be either large sedans, station wagons, intermediate or
full-sized automobiles, or utility and passenger-cargo trucks. Vehicles
can be powered by front-wheel, rear-wheel, or four-wheel drive.

**(2)** Be equipped with either standard disc and/or drum brakes as long
as they are maintained according to the manufacturer's performance
requirements. They can also qualify if they have a single sensor ABS
(anti-lock braking system) installed on the rear axle. Decelerometers
should not be installed on vehicles that are equipped with full ABS
because the ABS tends to distort the sensitivity of the decelerometer
resulting in friction readings that are lower than actually exist. In
addition, differences in ABS systems result in high variations in
friction readings. This could result in the premature closing of
runways. A full ABS has three sensors, one on each front wheel and one
on the rear axle. Decelerometers can be installed on these vehicles only
if the manufacturer of the ABS approves disengagement of the sensors on
the front wheels. If this modification can be satisfactorily achieved,
the vehicle's brake system then becomes a single sensor ABS installed on
the rear axle, which will then qualify the vehicle for conducting
friction tests with decelerometers.

**(3)** Be equipped with heavy-duty suspension and shock absorbers to
minimize the rocking or pitching motion during the application of
brakes. The weight should be distributed equally to the front and rear
axle of the vehicle. Ballast can be added to achieve and maintain this
distribution.

**(4)** Have tires made from the same construction, composition, and
tread configuration. Inflation pressure must be maintained according to
the vehicle manufacturer's specifications. When tread wear is excessive
on any one tire on the vehicle and/or exceeds 75 percent of the original
tread, all four tires on the vehicle must be replaced with new tires.

**c.** Capable of measuring the deceleration of the vehicle from speeds
greater than or equal to 15 mph (24 km/h) to an accuracy of 0.02 g.

**d.** Capable of providing deceleration values upon request of the
operator.

**e.** Capable of consistently repeating friction averages throughout
the friction range on all types of compacted snow and/or ice-covered
runway pavement surfaces.

**f.** Not affected by changes in vehicle velocity.

**g.** Not affected by change in personnel or their performance in
brake-applied decelerations.

**h.** Capable of providing the vehicle operator with a readily visible
deceleration reading.

[]{#__RefHeading___Toc213137159 .anchor}**A4-3. Certification
(Electronic Only).** The manufacturer must certify electronic
decelerometers are---

**a.** Capable of providing the deceleration values in recorded order,
enabling the average friction value for any length of runway to be
either electronically or manually calculated.

**b.** Capable of providing average deceleration values for touchdown,
midpoint, and rollout zones of the runway and the average friction value
for the entire runway tested. These averages must be automatically
calculated by the decelerometers, thus eliminating potential human error
when calculated manually.

**c.** Capable of storing a minimum of 21 deceleration values via the
internal microprocessor memory.

**d.** Capable of providing a hard copy printout of stored deceleration
values at the end of the testing period. The printout will record at
minimum---

**(1)** The date.

**(2)** The time.

**(3)** The runway designation or heading.

**e.** Capable of providing further information, which may be recorded
at the manufacturer's discretion, e.g., make of decelerometer,
ambient/pavement temperature, airport name and location, and operator
identification.

[]{#__RefHeading___Toc213137160 .anchor}**A4-4. Decelerometer
Calibration.** The decelerometer must be calibrated by the manufacturer
before shipping to the airport operator. The manufacturer must provide
the airport operator with a certificate of calibration, including test
results of the calibration. The manufacturer must provide a 1-year
warranty for the decelerometer. The manufacturer must provide the
airport operator with a recommended frequency for factory calibration of
the decelerometer.

[]{#__RefHeading___Toc213137161 .anchor}**A4-5. Training.** The
manufacturer must provide the airport operator with training manuals
and/or videos of all relevant data concerning friction measuring
recording and reporting, including---

**a.** An outline of the principles involved in the operation of the
decelerometer-type friction-measuring device.

**b.** Copies of pertinent ACs.

**c.** Procedures for reporting results of the friction tests in NOTAM
format.