PORT_A_LINK_FAULT PORT_B_LINK_FAULT PORT_RING_LINK_FAULT comm_status alarms
Applicable alarms (3)
Likely outcomes — click to expand
Based on 747 missions where this alarm fired in the last
90 days
(for PORT_B_LINK_FAULT) as of 2026-10-13
Grounding vs discrepancy (of 363 ZERP issues filed on these missions)
Top work orders
- EV2/EV3 Perform Preflight Without Motors · INSPECTION 82
- Perform Software Update on Aircraft · MAINTENANCE_ACTION 64
- EV2: Displace and Reinstall Hover Motor on Aircraft · MAINTENANCE_ACTION 42
- DISTRO_A_TO_HOVER_SF_ETHERNET_LINK Inspection · TROUBLESHOOTING 41
- EV2: Replace Aft Motor Assembly on Aircraft · MAINTENANCE_ACTION 35
Frequently replaced parts
| Part | P/N | Removals |
|---|---|---|
| CCW HOVER MOTOR ASSY, ZIP, P2 | 19607 | 277 |
| AFT MOTOR ASSY, ZIP, P2 | 23548 | 245 |
| PREPPED HOVER HARNESSING, STBD, ZIP, P2 | 0117583 | 214 |
| CW HOVER MOTOR ASSY, ZIP, P2 | 33333 | 203 |
| PREPPED HOVER HARNESSING, PORT, ZIP, P2 | 0117554 | 178 |
Frequently co-occurring alarms (% of the 747 missions above)
Aggregated from fleet operations and refreshed daily. Individual outcomes may vary by site and configuration.
These troubleshooting steps are applicable to the following alarms:
- PORT_A_LINK_FAULT
- PORT_B_LINK_FAULT
- PORT_RING_LINK_FAULT
Background
Section titled “Background”This alarm is triggered if a fault was detected with one of the network links that service the Hovers, Tail Bridge and Distros.
We monitor and alarm on the Distro ring ports, the Hover a and b and Tail Bridge a and b ports.
These alarms can fail the Takeoff task or cause a DockASAP.
The following diagrams show how each link connects different LRUs on EV2 and EV3. Note that each link includes three to five separate LRUs, including one or two harnesses.
Troubleshooting Steps
Section titled “Troubleshooting Steps”graph TD
open-failed-maintenance-validators["<small><b>Step 1</b></small><br/>Telemetry: Load the failed maintenance validator..."]
look-for-failing-checks{"<small><b>Step 2</b></small><br/>Question: Did any check fail for mx_ethernet_l..."}
check-failure-table["<small><b>Step 3</b></small><br/>Action: Find the failing check in the table b..."]
escalate-p2-fw-platform{{"<small><b>Step 4</b></small><br/>Escalation: Escalate to P2 Firmware Platform On C..."}}
open-failed-maintenance-validators --> look-for-failing-checks
look-for-failing-checks -->|Yes| check-failure-table
look-for-failing-checks -->|No| escalate-p2-fw-platform
style look-for-failing-checks fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style check-failure-table fill:#dcfce7,stroke:#22c55e,color:#14532d
style escalate-p2-fw-platform fill:#fef3c7,stroke:#f59e0b,color:#78350f Hover or focus a block to preview it. Select the block to keep the preview open.
mx_ethernet_link and mx_ethernet_node.NOTE: Validator results may take 15-30 minutes after the flight ends to appear on Baraza.
mx_ethernet_link or mx_ethernet_node?If no checks are seen failing but the
PORT_*_LINK_FAULT is still triggered, escalate to P2 Firmware Platform On Call.Resolution note
This plaintext block is ready to paste into the Resolution Note field on the ZERP issue you're working. The permalink below gives engineering review access to the full step-by-step timeline including any back-navigation; share it if the case needs a deeper look.
Permalink:
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Find the failing checks in the table below and follow the related inspection guide.
If no checks are seen failing but PORT_*_LINK_FAULT is still triggered, escalate to P2 Firmware Platform On Call.
| Failed Check | Interpretation | Inspection Guide |
|---|---|---|
| DISTRO_A_ETH_SWITCH_RECONFIGURED | Ethernet switch reconfiguration detected on Distro-A | Go To Inspection Guide |
| DISTRO_A_TO_HOVER_SF_ETHERNET_LINK_INTEGRITY | Distro-A to Hover-SF Ethernet Link Failure | Go To Inspection Guide |
| HOVER_PA_TO_TAIL_NODE_ETHERNET_LINK_INTEGRITY | Hover-PA to Tail Node Ethernet Link Failure | Go To Inspection Guide |
| HOVER_PF_TO_DISTRO_B_ETHERNET_LINK_INTEGRITY | Hover-PF to Distro-B Ethernet Link Failure | Go To Inspection Guide |
| HOVER_SA_TO_HOVER_PA_ETHERNET_LINK_INTEGRITY | Hover-SA to Hover-PA Ethernet Link Failure | Go To Inspection Guide |
| HOVER_SF_TO_HOVER_SA_ETHERNET_LINK_INTEGRITY | Hover-SF to Hover-SA Ethernet Link Failure | Go To Inspection Guide |
| TAIL_NODE_TO_HOVER_PF_ETHERNET_LINK_INTEGRITY | Tail Node to Hover-PF Ethernet Link Failure | Go To Inspection Guide |
| TAIL_NODE_TO_MIXED_MOTOR_ETHERNET_LINK_INTEGRITY | Tail Node to Mixed Motor Ethernet Link Failure | Go To Inspection Guide |
| DISTRO_TO_WINCH_ETHERNET_LINK_INTEGRITY | Winch Ethernet Link Failure | Go To Inspection Guide |
| HOVER_PA_TO_HOVER_PF_ETHERNET_LINK_INTEGRITY | Hover-PA to Hover-PF Ethernet Link Failure | Go To Inspection Guide |
| DISTRO_A_COMMS_MISSING | Distro-A likely powered down | Go To Inspection Guide |
| DISTRO_B_COMMS_MISSING | Distro-B likely powered down | Go To Inspection Guide |
| HOVER_PA_COMMS_MISSING | Hover-PA likely powered down | Go To Inspection Guide |
| HOVER_PF_COMMS_MISSING | Hover-PF likely powered down | Go To Inspection Guide |
| HOVER_SA_COMMS_MISSING | Hover-SA likely powered down | Go To Inspection Guide |
| HOVER_SF_COMMS_MISSING | Hover-SF likely powered down | Go To Inspection Guide |
| TAIL_NODE_COMMS_MISSING | Tail-Node likely powered down | Go To Inspection Guide |
| MIXED_MOTOR_COMMS_MISSING | Mixed motor Ethernet or power issue | Go To Inspection Guide |
| WINCH_COMMS_MISSING | Winch motor Ethernet or power issue | Go To Inspection Guide |
| HOVER_PA_BOOT_FAILURE | Hover-PA likely failed to boot into main app | Go To Inspection Guide |
| HOVER_PF_BOOT_FAILURE | Hover-PF likely failed to boot into main app | Go To Inspection Guide |
| HOVER_SA_BOOT_FAILURE | Hover-SA likely failed to boot into main app | Go To Inspection Guide |
| HOVER_SF_BOOT_FAILURE | Hover-SF likely failed to boot into main app | Go To Inspection Guide |
| TAIL_NODE_BOOT_FAILURE | Tail-Node likely failed to boot into main app | Go To Inspection Guide |
| MIXED_MOTOR_BOOT_FAILURE | Mixed Motor likely failed to boot into main app | Go To Inspection Guide |
| WINCH_BOOT_FAILURE | Winch likely failed to boot into main app | Go To Inspection Guide |
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