Users Manual Part 1

ALL

EFFECTIVITY

Page 2-22

22 Apr 2019

23-15-49

SYSTEM DESCRIPTION, INSTALLATION, AND MAINTENANCE MANUAL

ASPIRE-400

NOTE: The SDU can be strapped as SDU1 or SDU2.

(2) The SDU enters Standalone Configuration if the ORT is configured for Standalone

(3) When in Standalone Configuration, the ACD asserts its Dual System Select (DSS)

discrete.

C. Dual Safety SATCOM (Warm Standby)

(1) When the ORT is configured for Dual Safety SATCOM, the SDU can be in an Active state

or a Standby state. The SDU is only allowed to transmit when in the Active state. When in

the Standby state, the SDU is not allowed to transmit over the RF interface.

(2) In Dual Safety SATCOM configuration, both SATCOM can provide safety voice and data

services. Both have independent RF chains and antennas but only one can be active and

logged onto safety services at any one time.

(3) The SDU considers itself "SDU in coverage" when:

(a) The SDU has a valid spot beam map from the spot beams listed on the global

beam common channel.

(b) And is in coverage for its current location.

(4) When the SDU does not have a valid spot beam map, the SDU considers itself as "SDU

in coverage" when:

(a) SDU can see a satellite that has elevation angle > - 4 degrees.

(5) When ORT configured for Dual Safety SATCOM, on entering the Active state, the SDU:

(a) Asserts its DSS discrete before enabling RF transmission (this will assert the

companion SDU DSD discrete).

(b) Enables its RF transmission.

(d) Continues to assert its DSS discrete as long as it is in the Active state.

(6) When ORT configured for Dual Safety SATCOM, on entering the Standby state, the SDU:

(a) Terminates all user services (if any).

(b) Logs off (if logged on).

(d) De-asserts its DSS discrete (this will release the other SDU DSD discrete).

(e) Sets Bit 18 of Label 270 SDU "ACARS" MU/CMU Status Word to "1", and

continues to de-assert its DSS discrete as long as it is in Standby state.

D. Aircraft Directed Dual Safety SATCOM (Warm Standby)

(1) In Aircraft Directed Dual Safety SATCOM configuration, the SDU powers up in Standby

state and waits until it receives directions to go to Active state. Switching decisions are

aircraft directed and not determined by the SATCOM systems using the crosstalk bus.

(2) Communication and control of the SDU in an Aircraft Directed Dual Safety SATCOM

Configuration are via:

(a) Dual System Disable (DSD)

(b) Dual System Select (DSS)

DRAFT

3rd rvw Draft as of:

29 January, 2020