Low Level Wind Shear Alert System

Relocation/Sustainment (LLWAS-RS)

Product Output Formats

Engineering Report

Federal Aviation Administration

September 25, 1998

1\. **[Introduction]{.underline}**. This Engineering Report provides the
requirements for LLWAS product output format displays and their
selection and provides auxiliary requirements for single tower and
multiple tower airports. The outputs of the Government furnished weather
product algorithms require additional processing to provide a usable
product to end‑users. This engineering report describes the method of
selecting and providing the site specific information needed by the
LLWAS-RS in order to meet system requirements for fully automatic
operation. This report is to be used in conjunction with the weather
product algorithms. This report has been written using specification
formats and language in order to provide maximum clarity as to the
requirements.

2\. **[Applicable Documents]{.underline}**.

None.

3\. **[Requirements]{.underline}**.

3.1 **[Product Format]{.underline}**. This report provides format
requirements for LLWAS-RS weather products. The outputs of the
government furnished product algorithms require additional processing in
order to provide a usable product to end‑users.

3.1.1 **[Application]{.underline}**. The requirements in this report
apply to the LLWAS-RS Ribbon Displays Terminal (RBDT) and display
selection device (DSD) except as noted otherwise. LLWAS information as
specified in the following paragraphs **[SHALL]{.underline}** be
displayed at each local controller position in one or more control
towers.

3.1.2 **[RBDT Displays]{.underline}**. The RBDT consists of a 250
character (10 lines of 25 characters per line) DC plasma display panel,
drive circuitry, display controller, audible alarm, enclosure and
illuminated control panel.

3.1.3 **[Alphanumeric Displays]{.underline}**. \"RESERVED\"

3.1.4 **[Display Selection Device (DSD)]{.underline}**. The DSD
**[SHALL]{.underline}** be used to configure up to eight Ribbon Display
Terminals with up to eight of the 100 pre-selected runway
configurations.

3.1.5 **[Noted for Attention]{.underline}**.

3.1.5.1 **[Runway Definitions]{.underline}**. Some airports have 2 or 3
runways with the same heading. These are called parallel runways on the
display. They are differentiated by L or R (Left or Right, in the case
of 2 runways) and L, C, R (Left, Center, Right, in the case of 3
runways). If there is only one runway with a particular heading, then a
\"‑\" is displayed in this position.

An operational runway will be identified by a runway heading appended to
an \"A\" or a \"D\" to indicate the approach or departure operational
runway, respectively. For example, runway heading \"04\" is identified
as the following operational runways:

1.  04LA and 04LD for Left Approach and Left Departure.

2.  04RA and 04RD for Right Approach and Right Departure.

3.  04CA and 04CD for Center Approach and Center Departure.

4.  04‑A and 04‑D for Approach and Departure.

FAA assigned runway headings may differ slightly from geographic or
geomagnetic headings.

3.1.5.2 **[Display Selection Device Usage]{.underline}**. The DSD is
used to select a runway configuration to be displayed on a Ribbon
Display Terminal (RBDT). Each device controls the runway configurations
displayed on up to eight RBDTs for a single tower. For any RBDT, there
are 100 possible runway configurations that can be displayed.

The LLWAS‑RS Master Station **[SHALL]{.underline}** provide a separate
connection for each display selection device. The LLWAS‑RS Master
Station **[SHALL]{.underline}** be able to interface with at most 3
display selection devices.

3.1.5.2.1 **[Single Tower Facilities]{.underline}**. There is a single
display selection device and a single chain of up to 8 RBDTs connected
to the LLWAS‑RS Master Station. All 100 runway configurations are
available for each RBDT.

3.1.5.2.2 **[Multiple Tower Facilities]{.underline}**. Each tower has
its own display selection device and its own chain of up to eight RBDTs
connected to the LLWAS‑RS Master Station. All 100 runway configurations
are available to each RBDT. Each tower is segregated from the others so
that display selection device commands from one tower can affect only
the RBDTs in the tower in which the display selection device resides.

3.2 **[RBDT Message Element Selection]{.underline}**. Message elements
selection from the set of possible message elements enumerated in the
following paragraphs **[SHALL]{.underline}** be site adaptable.

3.2.1 **[Display Format for Lines 3 to 10]{.underline}**.

3.2.1.1 **[Non‑Alert Output]{.underline}**. In a non‑alert output, the
following information **[SHALL]{.underline}** be displayed:

a\) Operational Runway Identifier and Threshold Wind direction and
Speed:

1.) Operational Runway Identifier. The characters \"ffgh\" to identify
the operational runway to which the event location is referenced. The
operational runway identifier **[SHALL]{.underline}** be composed of two
decimal digits \"ff\" indicating FAA assigned runway heading, an
optional letter \"g\" to indicate Left, Center, or Right runway for
airports with parallel runways, or \"‑\" if there is no parallel runway,
and letter \"h\" to indicate the Approach or Departure runway corridor.
The operational runway identifier **[SHALL]{.underline}** be displayed
left justified. For example: \"35LA\" would indicate operational runway
35 Left Approach.

  ------ ----------------------------- ------ -----------------------------
  a.)    LA ‑ left approach            e.)    CA ‑ center approach

  b.)    LD ‑ left departure           f.)    CD ‑ center departure

  c.)    RA ‑ right approach           g.)    ‑A ‑ approach

  d.)    RD ‑ right departure          h.)    ‑D ‑ departure
  ------ ----------------------------- ------ -----------------------------

2.) Average Threshold Wind Direction and Speed. The characters \"ddd\"
to indicate threshold wind direction **[SHALL]{.underline}** be in
degrees, rounded to the nearest ten degrees, from ten to three hundred
and sixty degrees (010 ‑ 360). This **[SHALL]{.underline}** be the
indication of the direction from which the wind is blowing.

The characters \"ss\" to indicate threshold wind speed
**[SHALL]{.underline}** be in knots from three to ninety‑five (03 ‑ 95)
in one knot increments. Wind speed less than three knots
**[SHALL]{.underline}** be represented as \"CALM \" in the positions
normally occupied by the wind direction and speed.

Threshold wind speed and direction **[SHALL]{.underline}** be averaged
over 30 seconds.

b.) Blank spaces **[SHALL]{.underline}** be used to separate the label
for the Operational Runway Identifier, and thirty second average
Threshold Wind Direction and Speed.

c.) Refer to Figure 1 for a graphical representation.

3.2.1.2 **[Alert Output]{.underline}**. In an alert output, the
following information **[SHALL]{.underline}** be displayed:

a.) Operational Runway Identifier, Type of Alert, Estimated Loss or
Gain, Operational Runway Location, Threshold Wind Direction and Speed
and Possible Wind Shear Outside Network:

1.) The characters \"ffgh\" to identify the operational runway to which
the event location is referenced. The operational runway identifier
**[SHALL]{.underline}** be composed of two decimal digits \"ff\"
indicating FAA assigned runway heading, an optional letter \"g\" to
indicate Left, Center, or Right runway for airports with parallel
runways, or \"‑\" if there is no parallel runways, and a letter \"h\" to
indicate the Approach or Departure runway corridor. The operational
runway identifier **[SHALL]{.underline}** be displayed left justified.
For example: \"35LA\" would indicate operational runway 35 Left
Approach.

  ------ ----------------------------- ------ -----------------------------
  a.)    LA ‑ left approach            e.)    CA ‑ center approach

  b.)    LD ‑ left departure           f.)    CD ‑ center departure

  c.)    RA ‑ right approach           g.)    ‑A ‑ approach

  d.)    RD ‑ right departure          h.)    ‑D ‑ departure
  ------ ----------------------------- ------ -----------------------------

2.) Type of Alert. Characters to identify the type of alert being
reported. The type of alert reported **[SHALL]{.underline}** be as
follows:

> \(a\) Microburst Alert. The letters \"MBA\" to indicate a microburst
> alert.
>
> \(b\) Wind Shear Alert. The letters \"WSA\" to indicate a wind shear
> alert.

3.) Estimated Loss or Gain. The characters \"mmK‑\" to indicate the
estimated loss of the microburst or wind shear, or \"mmK+\" to indicate
the estimated gain of the wind shear. The estimated loss
**[SHALL]{.underline}** be composed of two decimal digits \"mm\", the
letter \"K\" to indicate knots, and negative sign \"‑\". The estimated
gain **[SHALL]{.underline}** be composed of two decimal digits \"mm\",
the letter \"K\" to indicate knots, and a positive sign \"+\".

4.) Operational Runway Location. The characters \"xMF\", \"yMD\", or
\"RWY\" to indicate the location of the event. The message element
**[SHALL]{.underline}** be composed of the letters \"RWY\", one decimal
digit \"x\" followed by the letters \"MF\", or one decimal digit \"y\"
followed by the letters \"MD\", where x = 1, 2, 3 off the approach end
and y = 1, 2 off the departure end of the runway, respectively.

5.) Average Threshold Wind Direction and Speed. The characters \"ddd\"
to indicate threshold wind direction **[SHALL]{.underline}** be in
degrees, rounded to the nearest ten degrees, from ten to three hundred
and sixty degrees (010 ‑ 360). This **[SHALL]{.underline}** be the
indication of the direction from which the wind blowing.

The characters \"ss\" to indicate threshold wind speed
**[SHALL]{.underline}** be in knots, from three to ninety‑five (03 ‑ 95)
in one knot increments. Wind speed less than three knots
**[SHALL]{.underline}** be represented as \"CALM\" in the positions
normally occupied by the wind direction and speed.

Threshold wind speed and direction **[SHALL]{.underline}** be averaged
over 30 seconds.

6.) Possible Wind Shear Outside Network. The character \"\*\"
**[SHALL]{.underline}** be used to indicate a possible wind shear
outside network.

b.) A blank space **[SHALL]{.underline}** be used to separate the label
for the Operational Runway Identifier, Type of Alert, Estimated Loss or
Gain, Operational Runway Location, and thirty second average Threshold
Wind Direction and Speed.

c.) Refer to Figure 1 for graphical representation.

3.2.2 **[System Status Message Format for Line 1]{.underline}**. The
following status information **[SHALL]{.underline}** be displayed while
in the real time and system support states:

a.) A status message **[SHALL]{.underline}** be displayed on line 1 of
the RBDT. The message format **[SHALL]{.underline}** contain the 2
minute averaged Center Field Wind direction and speed and gust speed,
LLWAS system time (hours and minutes), and while in the real time state,
the audible alarm state indicator (\"ON\" or \"OFF\"). The status
message elements **[SHALL]{.underline}** be displayed in fixed column
positions.

1.) CF Wind Direction and Speed. The characters \"ddd\" to indicate
center field wind direction **[SHALL]{.underline}** be in degrees,
rounded to the nearest ten degrees, from ten to three hundred and sixty
degrees (010 ‑ 360). This **[SHALL]{.underline}** be the indication of
the direction from which the wind is blowing.

The characters \"ss\" to indicate center field wind speed
**[SHALL]{.underline}** be in knots, from three to ninety five (03 ‑ 95)
in one knot increments. Wind speed less than three knots
**[SHALL]{.underline}** be represented as \"CALM\" in the positions
normally occupied by the wind direction and speed.

2.) CF Wind Gust Speed. The letter \"G\" **[SHALL]{.underline}** be used
to identify the gusts. The CF wind gust speed **[SHALL]{.underline}** be
in knots. The gust value **[SHALL]{.underline}** be displayed (2
characters) if the wind meets the gust criteria in the LLWAS Wind Gust
Algorithm defined in Appendix D, otherwise blanks
**[SHALL]{.underline}** be displayed in place of the letter \"G\" and
the gust value.

3.) System Time. Time **[SHALL]{.underline}** be displayed in the time
standard in which it was received. Current system time
**[SHALL]{.underline}** be displayed in the following format:

> \"HHMM\" (hoursminutes)

4.) Alarm State. The alarm state **[SHALL]{.underline}** indicate the
status of the RBDT audible alarm volume control. The state of this
control is provided by the audible alarm status indicator in the RBDT
status byte. \"ALM ON\" **[SHALL]{.underline}** indicate that the RBDT
alarm volume control is in the ON or Enabled position. \"ALM OFF\"
**[SHALL]{.underline}** indicate that the RBDT alarm volume control is
in the OFF or Disabled position.

b.) Refer to Figure 1 for a graphical representation.

c.) A blank space **[SHALL]{.underline}** be used to separate the label
\"CF\", the CF two minute average Wind Direction and Speed, Gust, system
time, and alert state, except for item d below.

d.) When the gust speed is displayed, the letter \"G\"
**[SHALL]{.underline}** be used to separate the 2 minute averaged wind
speed and gust speed.

3.2.3 **[Other Display Requirements]{.underline}**.

3.2.3.1 **[Initialization]{.underline}**. There **[SHALL]{.underline}**
not be any LLWAS information displayed until initialization has
completed. During initialization, "LLWAS INITIALIZING"
**[SHALL]{.underline}** be displayed on the system status line of the
RBDT.

3.2.3.2 **[Clear Message]{.underline}**. An alert message
**[SHALL]{.underline}** be deleted from the alphanumeric product display
within 30 +/- 2 seconds after the corresponding microburst(s) or wind
shear has moved outside of an active operational runway. (A microburst
or wind shear is considered to have moved outside of an active
operational runway when it has been determined that it has stopped
persisting.)

3.2.3.3 **[Numerical Overflow]{.underline}**. A \"95\"
**[SHALL]{.underline}** be indicated as the estimated loss for an
alphanumeric microburst having an estimated loss greater than 95 knots.
Also "95" shall be indicated as the estimated gain for a windshear with
gain over 95 knots.

**[Figure 1:]{.underline}** A graphical representation of the ribbon
display with messages.

  -----------------------------------------------------------------------
  **C F 0 8 0 1 5 G 2 0 1 2 4 5 A L M O F F**

  **1 7 R A W S A 1 5 K + 3 M F 3 5 0 1 5 \***

  **1 7 L A W S A 1 5 K + 3 M F 3 5 0 1 5 \***

  **3 5 L A 1 7 0 1 5**

  **3 5 R A 3 5 0 1 5**

  **0 8 - A 3 5 0 1 4**

  **0 8 - D 1 8 0 1 4**

  **2 6 R A M B A 5 5 K - 1 M D 3 5 0 1 5**

  **2 6 L A M B A 5 5 K - 1 M D 3 5 0 1 5**
  -----------------------------------------------------------------------

.

Line 1: Status Line. LLWAS system status in accordance with paragraph
3.2.2.

Line 2: Blank Line

Line 3: Alert Output. Operational Runway Identifier, Wind Shear Alert,
Estimated Loss or Gain, Operational Runway Location, Threshold Wind
Direction and Speed and Possible Wind Shear Outside Network.

Line 4: Alert Output. Operational Runway Identifier, Wind Shear Alert,
Estimated Loss or Gain, Operational Runway Location, Threshold

Wind Direction and Speed and Possible Wind Shear Outside Network.

Line 5: Non‑Alert Output. Operational Runway Identifier and Threshold
Wind Direction and Speed.

Line 6: Non‑Alert Output. Operational Runway Identifier and Threshold
Wind Direction and Speed.

Line 7: Non‑Alert Output. Operational Runway Identifier and Threshold

Wind Direction and Speed.

Line 8: Non‑Alert Output. Operational Runway Identifier and Threshold
Wind Direction and Speed.

Line 9: Alert Output. Operational Runway Identifier, Microburst Alert,
Estimated Loss or Gain, Operational Runway Location, Threshold Wind
Direction and Speed.

Line 10: Alert Output. Operational Runway Identifier, Microburst Alert,
Estimated Loss or Gain, Operational Runway Location, Threshold Wind
Direction and Speed.

3.3 **[Alarms]{.underline}**. The LLWAS **[SHALL]{.underline}** issue
alphanumeric alarm messages and audible alarms as described below.

3.3.1 **[Ribbon Display Terminal (RBDT) Visual Alarm]{.underline}**.
Alphanumeric alarm message(s) **[SHALL]{.underline}** be indicated by
flashing the text, or part of the text, on the ribbon display status
line, only if the display previously contained no alarm message(s).
Alphanumeric text **[SHALL]{.underline}** stop flashing when
acknowledged by the operator, or upon expiration of the Alphanumeric
Alarm Period. A site adaptable Alphanumeric Alarm Period with one (1)
second resolution and a default value of five (5) seconds
**[SHALL]{.underline}** be provided. Once acknowledgment of any visual
alarm has been made or upon expiration of the Alphanumeric Alarm Period,
the status text **[SHALL]{.underline}** be displayed "flashing" only if
the display previously contained no alarm message.

3.3.2 **[Audible Alarms]{.underline}**. The LLWAS
**[SHALL]{.underline}** initiate audible alarms for alphanumeric alarm
messages.

3.3.3 **[Alphanumeric Display Audible Alarm]{.underline}**. An audible
alarm **[SHALL]{.underline}** be generated at an RBDT upon the display
of an alphanumeric alarm message, only if the display previously
contained no alarm message(s). The audible alarm **[SHALL]{.underline}**
stop sounding when acknowledged by the operator, or upon expiration of
the Alphanumeric Alarm Period.

3.4 **[Input Device for Runway Configuration Screens]{.underline}**. The
runway configuration **[SHALL]{.underline}** be displayed and changeable
by the tower cab supervisor as needed, as indicated below:

a.) Each RBDT displays the runway configuration for a specific local
controller position.

b.) Predefined runway configurations and ordering
**[SHALL]{.underline}** be selectable from the DSD located in each tower
cab and available to the tower cab supervisor. Preprogrammed runway
configurations and ordering will be provided as part of the adaptation
parameters in the Government furnished files (Appendix B).

c.) The input device **[SHALL]{.underline}** include visual feedback for
confirmation of correct input.

3.4.1 **[Input Devices for Multiple Tower Sites]{.underline}**. A
separate DSD **[SHALL]{.underline}** be provided for each tower at
multiple tower airports, thus providing each tower with the capability
of displaying unique information. In addition to the above requirements,
all DSDs located at multiple tower sites will meet the following
additional requirements:

The DSD and RBDTs within each tower **[SHALL]{.underline}** work as if
that tower is its own single tower facility. All constraints of
paragraph 3.4 **[SHALL]{.underline}** apply to each tower.

4\. **[Qualification Requirements]{.underline}**. This section is not
applicable to this Engineering Report.

5\. **[Preparation for Delivery]{.underline}**. This section is not
applicable to this Engineering Report.

6\. **[Notes]{.underline}**.

6.1 **[Acronyms]{.underline}**.

  ------------- ---------------------------------------------------------
  ATC           Air Traffic Controllers

  DSD           Display Selection Device

  LLWAS         Low Level Wind Shear Alert System

  RBDT          Ribbon Displays Terminal
  ------------- ---------------------------------------------------------

6.2 **[Definitions]{.underline}**.

6.2.1 **[Site Adaptable]{.underline}**. Data that is airport specific
and modifiable.

6.2.2 **[Alert Message]{.underline}**. An alphanumeric message used to
inform ATC supervisors and controllers that a weather hazard is present
in an active operational runway.