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SAR Pattern Report (Encrypted)

Introduction/Additional information: 

Introduction

The Search Pattern Report (SPR) communicates a search pattern from the SAR Mission Coordinator (SMC) to a Search UNIT (SRU) (either to transmit a pattern for action or to cancel a pattern) or from a SRU to the SMC (reporting acceptance or completion). Search plan nomenclature is included for reference in Appendix 2 of this IDD.

Version 0:

This is an RTCM compliant update of the FID 2 message listed in the Oct 2014 EAIS IDD. The FID was changed to avoid confusion with ASMs used by the Saint Lawrence Seaway Corp.

The encrypted Message 8 isn’t implemented.

 

Permitted as from: 
12/05/2016
Registrant: 
USCG
Physical link: 
AIS
Message number (0=VDES-VDE): 
26
DAC or VPFI: 
366
FI / Message ID: 
13
Version: 
0
State: 
in force
State link: 
Expanding Square, Sector, Parallel Line & Creeping Line Search & Rescue (SAR) Pattern or Circle, Overlay Option 1
Number of slots (max): 
2
Last modified: 
29/01/2021 - 23:19
Used by: 
USCG
Details: 

 

 

 

Parameter

# of Bits

Description

 

 

Standard Message Header

Message ID

6

Identifier for Message 26; always 26.

Repeat Indicator

2

Indicates how many times a message has been repeated. 0 – 3; 0 = default; 3 = do not repeat any more. Set to zero (default).

Source MMSI

30

MMSI number of source station. Varies according to the transmitter ID.

 

Destination Indicator

 

1

0 = Broadcast (no Destination ID field used)

1 = Addressed (Destination ID uses 30 data bits for MMSI)

Set to 0, broadcast.

 

Binary Data Flag

 

1

0 = unstructured binary data (no Application Identifier bits used); 1 = binary data coded as defined by using the16-bit Application identifier.

Set to 1, structured.

Binary Data

Designated Area Code

10

Designated area code (DAC). This code is based on the maritime identification digits (MID). Set to 366.

Function Identifier

6

Function identifier. Set to 13.

Encrypted Payload

Version

3

Sequential number used to indicate the message version in steps of 1. 0 = test message = default; 1 – 7 = message version. Set to zero.

 

Message Linkage ID

 

10

Identifier for the SAR Pattern Report. This number uniquely identifies a search pattern sent from a given SMC (MMSI) and is used to connect additional information with the search. Source MMSI and this ID uniquely identify the event. Set to 1 - 1023 by message originator; 0 = not available.

 

Pattern Type

 

3

Type of search pattern:

0 = Expanding Square (SS) = default; 1 = Sector (VS); 2 = Parallel Line (PS); 3 = Creeping Line (CS); 4 – 7 = reserved.

 

 

 

 

 

 

 

 

 

 

Search Pattern Status

 

 

 

 

 

 

 

 

 

 

3

 

 

Binary Data

Encrypted Payload

Reference Time

UTC Day

5

UTC Day

1 – 31; 0 = UTC day not available = default.

UTC Hour

5

UTC Hour.

0 – 23; 24 = UTC hour not available = default; 25 - 31 = reserved.

UTC Min

6

UTC Minute.

0 – 59; 60 = UTC minute not available = default; 61 - 63 (reserved for future use)

Action SRU MMSI

30

MMSI of the Action SRU. This varies according to the MMSI of the desired unit. 0

= unknown = default;

 

Case ID Number

 

30

Case ID. Maximum 5 characters 6-bit ASCII as defined in ITU 1371-5, Table 47. “@@@@@” = not available = default.

If less than 5 characters, the remainder of the parameter should be filled with “@” characters (set bits to 0); but, not shown on the presentation.

Search Point

 

Longitude

 

25

Longitude in 1/1000 minute. (±180°)

East = positive (as per 2’s complement); West = negative (as per 2’s complement); 181° = not available = default.

 

Latitude

 

24

Latitude in 1/1000 minute (±90°)

North = positive (as per 2’s complement); South = negative (as per 2’s complement); 91° = not available = default.

 

Initial Heading

 

9

Direction of the first leg.

0 – 359 degrees; 360 = not specified = default; 361 – 510 = reserved; 511 = not to be used.

 

First Leg Length

 

12

Length of the first leg (lengths of succeeding legs depend upon the type of pattern) in 0.1 NM increments.

0 = not specified = default; 0.1 – 400.0 NM; 4001-4094 = reserved; 4095 = not to be used.

 

No. of Legs

 

10

Total number of legs (search and cross) to execute. 0 = not specified = default; 1 – 1000 legs;

1001-1022 = reserved; 1023 = not to be used.

 

Track Spacing

 

9

Track spacing in 0.1 NM increments.

0 = not specified = default; 0.1 – 50.0 NM; 501 – 510 = reserved; 511 – not to be used.

First Turn Direction

1

Direction of first turn.

0 = port; 1 = starboard = default.

Search Altitude

7

Altitude for search pattern in 50 ft increments.

0 = sea level; 50 – 6000 ft; 121 = not specified = default; 122 – 127 = reserved.

 

Search Speed

 

9

Speed to execute the search pattern in 1kt increments. 0 = not specified = default; 1 – 500 kts;

501 – 510 = reserved; 511 – not to be used.

Search Area Width

11

Total width of search area in tenths of NM

0 = unknown = default; 0.1 – 200.0 NM; 2001-2047 reserved.

Search Area Length

11

Total length of search area in tenths of NM

0 = unknown = default; 0.1 – 200.0 NM; 2001-2047 reserved.

Encryption Bit Padding

33

Sufficient spare bits to ensure that the binary data is a multiple of 128 bits for block encryption (256). Set to 0.

 

Checksum

 

16

 

16-bit CRC calculated as per EAIS Specification
               

 

Footer

Spare

4

Four extra bits added to ensure the message ends on a byte boundary.

Set to zero.

Communications State Selector

1

0 = SOTDMA communication state follows 1 = ITDMA communication state follows

 

Communications State

 

19

SOTDMA communication state (see ITU 1371-5 § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (§ 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1.

Total bits

352

2      Slot Binary Message
      1. Usage Notes
        • The Search execution status is controlled by the Search Pattern Status field. A State Diagram is shown in Figure 1 with the execution flow as follows:
          • The pattern is initially sent from the MC to the action SRU with the Status set as 0 (direction to execute a plan).
          • The SRU should respond with either:
            • Status set as 0 to indicate that the pattern was received and will be started (identical pattern parameters).
              • Status set to 7 to say the pattern cannot be executed.
          • If the SRU sends a status of 7 the MC needs to send a new pattern (followed up with communications between the MC and SRU to discuss WHY the pattern cannot be executed).
          • Once the search plan is started the SRU shall send a message with status 1 with the time and position fields updated to reflect the actual commence search time and position.
          • Once the pattern is complete the SRU should send the Search pattern report with a status of 2 and with the time and position fields updated to reflect time and position of completion.
          • If the SRU needs to abort the plan prior to completion a message with status=3 should be sent with the time and position fields updated to reflect time and position when aborted plan.
          • If the SMC wants to cancel a SAR pattern prior to completion then the message is sent with status = 3.
 

 

 

Figure 1: SAR Plan Message State Diagram

 

        • The Message Linkage ID can be used to link additional text (e.g., a separate Linked Text message). However, the same source MMSI needs to be included in both the SPR and the Linked Text Message (LTM). This could be used to communicate a SAR pattern designation or additional notes about the pattern or search object.
        • A message version number is encoded as part of the message; if the received version number is different than what the display system has been programmed for, then the charting system should alert the user to the difference.
        • All headings are in degrees true.
        • All positions are in WGS 84 Datum.
        • If less than 5 characters, the remainder of the Case ID parameter should be filled with “@” characters (set bits to 0); but, not shown on the presentation.
        • For the expanding square search the track spacing should equal the first leg length; to ensure this is true the value should be specified in the first leg length field and track spacing field set to 0.
        • For the Message 26 version, the 20 bits Communications State are added by the transmitter if transmission is initiated by a BBM sentence.
 

 

        1. Expanding Square Search (SS) Parameters

An expanding square search pattern uses the following parameters:

        • CSP
        • Initial heading
        • Track spacing
        • Direction of turns (L/R)

All turns are 90°, typically to starboard. Each even turn, increase the distance of the leg by 1 track space. See Figure 1 within Appendix 2 of this VDL. For this pattern track spacing and initial leg length are the same and both fields should be set to the same value.

        1. Sector Search (VS) Parameters

A sector search pattern uses the following parameters:

        • CSP
        • Initial heading
        • Leg length
        • Number of legs (defined as the equal-length segments)

All turns are 120° to starboard, and all legs are of equal length. The legs are the equal length segments (from CSP to radius of the circle). It takes 9 equal length legs to complete one VS pattern (less than 9 legs can be specified if the full pattern is not desired). After completing 9 equal length legs (back to the CSP) the pattern can be repeated with a new initial heading 30° to starboard of the initial. So if the number of legs specified is greater than 9, after 9 legs, rotate the pattern 30° to the right and continue. After 18 legs, rotate the pattern another 30° to the right. See Figure 2 within Appendix 2 of this VDL.

 

        1. Parallel Search (PS) Parameters

A parallel search pattern uses the following parameters:

        • CSP
        • Initial direction
        • Leg length
        • Track spacing
        • First turn (L/R)

All turns are 90° – 2 turns in same direction then switch direction. Cross leg lengths are equal to track spacing. Go leg length, turn go track space, turn same direction go leg length, turn opposite direction go track space, turn same, etc. See Figure 3 within Appendix 2 of this VDL.

        1. Creeping Line Search (CS) Parameters

The creeping line search is the same as the parallel search except that the search legs are oriented along the minor axis of the search area vice the major axis.

 

Attachment: 
PDF icon eais_idd_v5_4_8may17.pdf