Tail Model Mismatch
Viewing this guide for
Applicable alarms (2)
TAIL_PORT_MODEL_MISMATCHTAIL_STBD_MODEL_MISMATCH
Likely outcomes — click to expand
Based on 407 missions where this alarm fired in the last
90 days
(for TAIL_PORT_MODEL_MISMATCH) as of 2026-10-13
Grounding vs discrepancy (of 76 ZERP issues filed on these missions)
Top work orders
- EV3: Inspect Aircraft after Droid Left Behind (DLB) · MAINTENANCE_ACTION 10
Frequently replaced parts
| Part | P/N | Removals |
|---|---|---|
| TAIL ASSY STBD(RH), PRE-EV2, ZIP, P2 | 21840 | 102 |
| TAIL, FIXED WING, PORT, ZIP, P2 | 31280 | 97 |
| BATTERY ASSY, ZIP, P2 | 27158 | 55 |
| ASSY, SPOOL AND LINE, DOCKING FIN | 48477 | 37 |
| TAIL ASM, STRBRD(RH), ZIP, P2 | 0108359 | 20 |
Frequently co-occurring alarms (% of the 407 missions above)
Aggregated from fleet operations and refreshed daily. Individual outcomes may vary by site and configuration.
Background
Section titled “Background”Use this guide only for tail model mismatch alarms. Prefer the matching tail servo-mismatch-feedback-gap validator result when it is available, because it is less error-prone than manual plot review. If validator processing is delayed, incomplete, or missing, use the manual Baraza sequence-delta plot path. If no comms fault is found, follow the suspect tail surface mechanism issue guide.
Troubleshooting Steps
Section titled “Troubleshooting Steps”graph TD
check-p2f-validator-results["<small><b>Step 1</b></small><br/>Action: **Start with the validator path.** It..."]
try-preferred-validator-check{"<small><b>Step 2</b></small><br/>Question: Try the preferred validator check now..."}
check-matching-tail-failure{"<small><b>Step 3</b></small><br/>Question: Did the matching tail servo-mismatch..."}
use-manual-plot-fallback["<small><b>Step 4</b></small><br/>Action: Use manual Baraza plot analysis while..."]
apply-control-surface-health-sequence-template["<small><b>Step 5</b></small><br/>Action: Apply the **Control Surface Health A..."]
check-sequence-delta-near-transition{"<small><b>Step 6</b></small><br/>Question: In the affected tail servo's surface ..."}
follow-servo-rs485("<small><b>Step 7</b></small><br/>Reference: This is indicative of unreliable comm...")
follow-suspect-tail-surface-mechanism-issue("<small><b>Step 8</b></small><br/>Reference: No comms fault was found. The surface...")
check-p2f-validator-results --> try-preferred-validator-check
try-preferred-validator-check -->|The matching validator chec...| check-matching-tail-failure
try-preferred-validator-check -->|The matching validator chec...| use-manual-plot-fallback
check-matching-tail-failure -->|Yes, the matching tail feed...| follow-servo-rs485
check-matching-tail-failure -->|No, there is no matching ta...| follow-suspect-tail-surface-mechanism-issue
use-manual-plot-fallback --> apply-control-surface-health-sequence-template
apply-control-surface-health-sequence-template --> check-sequence-delta-near-transition
check-sequence-delta-near-transition -->|The sequence number delta e...| follow-servo-rs485
check-sequence-delta-near-transition -->|The sequence number delta d...| follow-suspect-tail-surface-mechanism-issue
style check-p2f-validator-results fill:#dcfce7,stroke:#22c55e,color:#14532d
style try-preferred-validator-check fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style check-matching-tail-failure fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style use-manual-plot-fallback fill:#dcfce7,stroke:#22c55e,color:#14532d
style apply-control-surface-health-sequence-template fill:#dcfce7,stroke:#22c55e,color:#14532d
style check-sequence-delta-near-transition fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style follow-servo-rs485 fill:#f3e8ff,stroke:#a855f7,color:#581c87
style follow-suspect-tail-surface-mechanism-issue fill:#f3e8ff,stroke:#a855f7,color:#581c87 Hover or focus a block to preview it. Select the block to keep the preview open.
1 action
Start with the validator path. It is preferred because it is less error-prone than manual plot review.
Check validator results for this flight from the P2F validator results page. Do not use the P2M validator results page.
Open the Validators tab.
Check validator results for this flight from the P2F validator results page. Do not use the P2M validator results page.
Open the Validators tab.
2 question
Try the preferred validator check now.
1. Filter validator results to
2. Search for
3. Look for the check that matches the alarm:
-
-
If the matching check is unavailable, incomplete, or missing, use manual Baraza plot analysis.
1. Filter validator results to
zip_a only. Do not use Zip B results.2. Search for
servo-mismatch-feedback-gap.3. Look for the check that matches the alarm:
-
TAIL_PORT_MODEL_MISMATCH: servo-mismatch-feedback-gap/tail-port-mismatch-feedback-gap-
TAIL_STBD_MODEL_MISMATCH: servo-mismatch-feedback-gap/tail-stbd-mismatch-feedback-gapIf the matching check is unavailable, incomplete, or missing, use manual Baraza plot analysis.
3 question
Did the matching tail
-
-
Example failing validator result. The screenshot uses a wing-port check, but the failure pattern is the same for the tail checks listed above.
servo-mismatch-feedback-gap check fail?-
TAIL_PORT_MODEL_MISMATCH: check servo-mismatch-feedback-gap/tail-port-mismatch-feedback-gap-
TAIL_STBD_MODEL_MISMATCH: check servo-mismatch-feedback-gap/tail-stbd-mismatch-feedback-gapExample failing validator result. The screenshot uses a wing-port check, but the failure pattern is the same for the tail checks listed above.
4 action
Use manual Baraza plot analysis while validator results are delayed, incomplete, or missing.
This path is more subject to human error than the validator check. If the matching validator check becomes available before you finish, prefer the validator result.
This path is more subject to human error than the validator check. If the matching validator check becomes available before you finish, prefer the validator result.
5 action
Apply the Control Surface Health And Message Sequence template in Baraza. Locate the surface health plot for the tail servo that raised the alarm and use the
-
-
Use the sequence-delta plot to identify missing feedback messages. Do not count individual feedback dots or check whether position signals diverge on this fallback path.
message_sequence_number (delta) plot directly above it.-
TAIL_PORT_MODEL_MISMATCH: use the tail-port surface health and message sequence plots.-
TAIL_STBD_MODEL_MISMATCH: use the tail-starboard surface health and message sequence plots.Use the sequence-delta plot to identify missing feedback messages. Do not count individual feedback dots or check whether position signals diverge on this fallback path.
6 question
In the affected tail servo's surface health plot, find the
The examples below use wing surfaces, but the same threshold applies to tail surfaces.
Clear comms-fault example:
No comms-fault example:
OPERABLE_NOMINAL -> OPERABLE_HIGH_MISMATCH transition. In the message_sequence_number (delta) plot directly above it, does the sequence number delta ever exceed 3 near that transition?The examples below use wing surfaces, but the same threshold applies to tail surfaces.
Clear comms-fault example:
No comms-fault example:
7 reference
This is indicative of unreliable comms with the affected tail servo.
Follow the guide for servo RS-485 connection issues:
For follow-up actions and questions, escalate to P2 Avionics Hardware On Call.
Follow the guide for servo RS-485 connection issues:
Validator: servo_rs485_connection/*.For follow-up actions and questions, escalate to P2 Avionics Hardware On Call.
8 reference
No comms fault was found. The surface likely has a mechanism issue. Follow the suspect tail surface mechanism issue guide for the affected tail surface.
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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