Loss of the Frequency Control by the ATSU

TASK 46-21-00-810-836-A
Loss of the Frequency Control by the ATSU

1. Possible Causes

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 23-12-33-000-001	Removal of the VHF Transceiver
AMM 23-12-33-400-001	Installation of the VHF Transceiver
AMM 46-21-00-710-001	Operational Test of the ATSU
ASM 462104
ASM 462106
AMM 46-21-34-000-001	Removal of the Air Traffic Service Unit (ATSU)
AMM 46-21-34-400-001	Installation of the Air Traffic Service Unit (ATSU)

3. Fault Confirmation
Subtask 46-21-00-740-118-A

A. Test
(1) Do the fifth part of the operational test of the ATSU AMM 46-21-00-710-001.

4. Fault Isolation
Subtask 46-21-00-810-084-A

A. If, during the operational test, the ATSU cannot control the VHF3 frequency through one RMP:

(1) If there is no ground signal:

(a) If there is a ground signal:

(b) If the fault continues:

do a check and repair the wiring of the DFS PORT SELECT DISCRETE from the ATSU (1TX1) pin AA/12B to the VDR3 (1RC3) pin AB/11D ASM 462104.

1 If the fault continues:

do a check and repair the wiring of ATSU SYS5 OUTPUT BUS from the ATSU (1TX1) pins AA/1E,1F to the VDR3 (1RC3) pins AB/11A,11B ASM 462106.

Subtask 46-21-00-740-119-A

B. Do the test given in Para. 3.

[Rev.8 from Aug 2018] 2026.04.04 04:34:20 UTC