Tail Torque Mismatch
Viewing this guide for
Applicable alarms (2)
TAIL_PORT_TORQUE_MISMATCHTAIL_STBD_TORQUE_MISMATCH
Likely outcomes — click to expand
Based on 24 missions where this alarm fired in the last
90 days
(for TAIL_PORT_TORQUE_MISMATCH) as of 2026-10-13
Grounding vs discrepancy (of 2 ZERP issues filed on these missions)
Frequently co-occurring alarms (% of the 24 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 torque mismatch alarms.
Troubleshooting Steps
Section titled “Troubleshooting Steps”graph TD
check-p2f-validator-results["<small><b>Step 1</b></small><br/>Action: **Start with the servo comms validato..."]
try-servo-comms-validator-check{"<small><b>Step 2</b></small><br/>Question: Try the validator check now. 1. Filte..."}
check-matching-tail-failure{"<small><b>Step 3</b></small><br/>Question: Did the matching tail servo-mismatch..."}
follow-servo-rs485("<small><b>Step 4</b></small><br/>Reference: This is indicative of unreliable comm...")
inspect-flight-logs-no-validator["<small><b>Step 5</b></small><br/>Action: Use manual Baraza plot analysis to de..."]
apply-control-surface-high-mismatch-template["<small><b>Step 6</b></small><br/>Action: Apply the **Control Surface Torque M..."]
zoom-first-high-mismatch-transition["<small><b>Step 7</b></small><br/>Action: In the affected tail servo's gnc.veh..."]
check-feedback-dot-gaps{"<small><b>Step 8</b></small><br/>Question: In the second plot, immediately below..."}
follow-servo-rs485-from-feedback-gaps("<small><b>Step 9</b></small><br/>Reference: This is indicative of unreliable comm...")
inspect-flight-logs-validator-passed["<small><b>Step 10</b></small><br/>Action: Use manual Baraza plot analysis to de..."]
apply-control-surface-high-mismatch-template-skip-comms["<small><b>Step 11</b></small><br/>Action: Apply the **Control Surface Torque M..."]
zoom-first-high-mismatch-transition-skip-comms["<small><b>Step 12</b></small><br/>Action: In the affected tail servo's gnc.veh..."]
check-feedback-model-mismatch{"<small><b>Step 13</b></small><br/>Question: In the second plot for this surface, ..."}
check-torque-spikes{"<small><b>Step 14</b></small><br/>Question: Look at the third plot for this surfa..."}
request-tail-control-surface-inspection{"<small><b>Step 15</b></small><br/>Question: Request inspection on the affected ta..."}
replace-tail-control-surface-hardware["<small><b>Step 16</b></small><br/>Action: Create a work order to replace the ba..."]
escalate-structures-mechanisms{{"<small><b>Step 17</b></small><br/>Escalation: Escalate to Aircraft Structures & Mec..."}}
escalate-zip-controls-or-wait{{"<small><b>Step 18</b></small><br/>Escalation: Escalate to P2 Zip Controls On Call w..."}}
check-p2f-validator-results --> try-servo-comms-validator-check
try-servo-comms-validator-check -->|The matching validator chec...| check-matching-tail-failure
try-servo-comms-validator-check -->|The matching validator chec...| inspect-flight-logs-no-validator
check-matching-tail-failure -->|Yes, the matching tail feed...| follow-servo-rs485
check-matching-tail-failure -->|No, there is no matching ta...| inspect-flight-logs-validator-passed
inspect-flight-logs-no-validator --> apply-control-surface-high-mismatch-template
apply-control-surface-high-mismatch-template --> zoom-first-high-mismatch-transition
zoom-first-high-mismatch-transition --> check-feedback-dot-gaps
check-feedback-dot-gaps -->|Yes, there is a noticeable ...| follow-servo-rs485-from-feedback-gaps
check-feedback-dot-gaps -->|No, there is no noticeable ...| check-feedback-model-mismatch
check-feedback-dot-gaps -->|I do not know| escalate-zip-controls-or-wait
inspect-flight-logs-validator-passed --> apply-control-surface-high-mismatch-template-skip-comms
apply-control-surface-high-mismatch-template-skip-comms --> zoom-first-high-mismatch-transition-skip-comms
zoom-first-high-mismatch-transition-skip-comms --> check-feedback-model-mismatch
check-feedback-model-mismatch -->|Yes, the feedback diverges ...| request-tail-control-surface-inspection
check-feedback-model-mismatch -->|No, the feedback does not d...| check-torque-spikes
check-feedback-model-mismatch -->|I do not know| escalate-zip-controls-or-wait
check-torque-spikes -->|Yes, there appears to be an...| request-tail-control-surface-inspection
check-torque-spikes -->|No, the torque plot seems n...| escalate-zip-controls-or-wait
check-torque-spikes -->|I do not know| escalate-zip-controls-or-wait
request-tail-control-surface-inspection -->|Yes, inspection found an issue| replace-tail-control-surface-hardware
request-tail-control-surface-inspection -->|No, inspection found no issue| escalate-structures-mechanisms
style check-p2f-validator-results fill:#dcfce7,stroke:#22c55e,color:#14532d
style try-servo-comms-validator-check fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style check-matching-tail-failure fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style follow-servo-rs485 fill:#f3e8ff,stroke:#a855f7,color:#581c87
style inspect-flight-logs-no-validator fill:#dcfce7,stroke:#22c55e,color:#14532d
style apply-control-surface-high-mismatch-template fill:#dcfce7,stroke:#22c55e,color:#14532d
style zoom-first-high-mismatch-transition fill:#dcfce7,stroke:#22c55e,color:#14532d
style check-feedback-dot-gaps fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style follow-servo-rs485-from-feedback-gaps fill:#f3e8ff,stroke:#a855f7,color:#581c87
style inspect-flight-logs-validator-passed fill:#dcfce7,stroke:#22c55e,color:#14532d
style apply-control-surface-high-mismatch-template-skip-comms fill:#dcfce7,stroke:#22c55e,color:#14532d
style zoom-first-high-mismatch-transition-skip-comms fill:#dcfce7,stroke:#22c55e,color:#14532d
style check-feedback-model-mismatch fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style check-torque-spikes fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style request-tail-control-surface-inspection fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style replace-tail-control-surface-hardware fill:#dcfce7,stroke:#22c55e,color:#14532d
style escalate-structures-mechanisms fill:#fef3c7,stroke:#f59e0b,color:#78350f
style escalate-zip-controls-or-wait fill:#fef3c7,stroke:#f59e0b,color:#78350f Hover or focus a block to preview it. Select the block to keep the preview open.
1 action
Start with the servo comms validator.
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 validator check now.
1. Filter validator results to
2. Search for
3. Look for the check that matches the alarm:
-
-
Is the matching check available, or is it unavailable, incomplete, or missing?
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_TORQUE_MISMATCH: servo-mismatch-feedback-gap/tail-port-mismatch-feedback-gap-
TAIL_STBD_TORQUE_MISMATCH: servo-mismatch-feedback-gap/tail-stbd-mismatch-feedback-gapIs the matching check available, or is it unavailable, incomplete, or missing?
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_TORQUE_MISMATCH: check servo-mismatch-feedback-gap/tail-port-mismatch-feedback-gap-
TAIL_STBD_TORQUE_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 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.
5 action
Use manual Baraza plot analysis to determine next steps.
If no servo-comms validator results were available, first manually inspect for servo comms gaps. 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.
If no servo-comms validator results were available, first manually inspect for servo comms gaps. 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.
6 action
Apply the Control Surface Torque Mismatch template in Baraza. Locate the
-
-
There are 4 plots in the plot set for each surface:
1.
2. The affected surface's
3. The servo
4.
The screenshot below uses a wing-port example, but the plot pattern is the same for tail surfaces.
gnc.vehicle_health plot for the tail servo that raised the alarm.-
TAIL_PORT_TORQUE_MISMATCH: use the tail-port surface plots.-
TAIL_STBD_TORQUE_MISMATCH: use the tail-starboard surface plots.There are 4 plots in the plot set for each surface:
1.
gnc.vehicle_health state.2. The affected surface's
feedback.angle_rad vs the controller model line from actuator_states.delta_s.3. The servo
feedback.setpoints.torque and feedback.state.torque.4.
feedback.setpoints.omega_m vs state.omega_m (this 4th plot is not used in this guide).The screenshot below uses a wing-port example, but the plot pattern is the same for tail surfaces.
7 action
In the affected tail servo's
gnc.vehicle_health plot, find the first OPERABLE_NOMINAL -> OPERABLE_HIGH_MISMATCH transition. Zoom in around that transition until you can see the individual value dots. 8 question
In the second plot, immediately below the
Do you see any noticeable gaps in the feedback dots?
Each feedback sample should arrive every 20 ms. Any gap larger than 60 ms, or about 3 missing dots, is problematic. Use the plot cursor to measure the gap if needed.
OPERABLE_NOMINAL -> OPERABLE_HIGH_MISMATCH transition, compare the feedback.angle_rad dots against the actuator_states.delta_s model line.Do you see any noticeable gaps in the feedback dots?
Each feedback sample should arrive every 20 ms. Any gap larger than 60 ms, or about 3 missing dots, is problematic. Use the plot cursor to measure the gap if needed.
9 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.
10 action
Use manual Baraza plot analysis to determine next steps.
Here we will inspect for surface model mismatch or unusual servo torque feedback.
Here we will inspect for surface model mismatch or unusual servo torque feedback.
11 action
Apply the Control Surface Torque Mismatch template in Baraza. Locate the
-
-
There are 4 plots in the plot set for each surface:
1.
2. the affected surface's
3. the servo
and 4.
The screenshot below uses a wing-port example, but the plot pattern is the same for tail surfaces.
gnc.vehicle_health plot for the tail servo that raised the alarm.-
TAIL_PORT_TORQUE_MISMATCH: use the tail-port surface plots.-
TAIL_STBD_TORQUE_MISMATCH: use the tail-starboard surface plots.There are 4 plots in the plot set for each surface:
1.
gnc.vehicle_health state;2. the affected surface's
feedback.angle_rad vs the controller model line from actuator_states.delta_s;3. the servo
feedback.setpoints.torque and feedback.state.torque;and 4.
feedback.setpoints.omega_m vs state.omega_m (this 4th plot not used in this guide).The screenshot below uses a wing-port example, but the plot pattern is the same for tail surfaces.
12 action
In the affected tail servo's
gnc.vehicle_health plot, find the first OPERABLE_NOMINAL -> OPERABLE_HIGH_MISMATCH transition. Zoom in around that transition until you can see the individual value dots. 13 question
In the second plot for this surface, compare the
Do the feedback dots diverge significantly from the controller model line?
A significant divergence means the blue feedback dots remain visibly separated from the orange model line during the high-mismatch region.
feedback.angle_rad dots against the actuator_states.delta_s model line.Do the feedback dots diverge significantly from the controller model line?
A significant divergence means the blue feedback dots remain visibly separated from the orange model line during the high-mismatch region.
14 question
Look at the third plot for this surface, which has
Are there any noticeable torque spikes during the time immediately before we trigger 'OPERABLE_HIGH_MISMATCH'? These spikes might look larger, sharper or longer compared to the torque plots for the other non-faulted surfaces?
feedback.setpoints.torque and feedback.state.torque.Are there any noticeable torque spikes during the time immediately before we trigger 'OPERABLE_HIGH_MISMATCH'? These spikes might look larger, sharper or longer compared to the torque plots for the other non-faulted surfaces?
15 question
Request inspection on the affected tail control surface.
-
-
Prompt maintenance to follow UMM
Did the inspection find an issue with the affected control surface hardware?
-
TAIL_PORT_TORQUE_MISMATCH: inspect the port ruddervator.-
TAIL_STBD_TORQUE_MISMATCH: inspect the starboard ruddervator.Prompt maintenance to follow UMM
85.1.3.c Inspect Control Surface ("Ruddervator").Did the inspection find an issue with the affected control surface hardware?
16 action
Create a work order to replace the bad tail control surface hardware identified by inspection. Reference the affected side and attach the inspection findings to the ticket.
17 escalation
Escalate to Aircraft Structures & Mechanisms On Call. Tell them the affected tail control surface inspection found no issue, but the torque-mismatch evidence still suggests a stuck or binding surface.
18 escalation
Escalate to P2 Zip Controls On Call with the plot screenshots and what was unclear.
Resolution note
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