CELL_MODEM_FIRMWARE_MISMATCH
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Applicable alarms (1)
CELL_MODEM_FIRMWARE_MISMATCH
Likely outcomes — click to expand
Based on 171 missions where this alarm fired in the last 90 days as of 2026-10-13
Grounding vs discrepancy (of 5 ZERP issues filed on these missions)
Frequently replaced parts
| Part | P/N | Removals |
|---|---|---|
| ASSM, FLIGHT COMPUTER, AFT, ZIP, P2 | 48409 | 10 |
| ASSM, FLIGHT COMPUTER, FORE, ZIP, P2 | 48408 | 5 |
| AFT MOTOR ASSY, ZIP, P2 | 23548 | 4 |
Frequently co-occurring alarms (% of the 171 missions above)
Aggregated from fleet operations and refreshed daily. Individual outcomes may vary by site and configuration.
Background
Section titled “Background”Cell modem firmware updates are not yet supported in the field. A compute board swap is currently the only method available to resolve this issue.
Once cell modem firmware updates are available, this guide will be updated with recovery steps.
Troubleshooting Steps
Section titled “Troubleshooting Steps”graph TD
are-you-troubleshooting-an-ev2-or-ev3{"<small><b>Step 1</b></small><br/>Question: Are you troubleshooting an EV2 or EV3..."}
replace-the-affected-ev2-flight-compute["<small><b>Step 2</b></small><br/>Action: Replace the affected Flight Compute A..."]
determine-the-affected-ev3-compute["<small><b>Step 3</b></small><br/>Action: Determine whether the alarm is set on..."]
which-ev3-compute-has-the-alarm{"<small><b>Step 4</b></small><br/>Question: Which compute has CELL_MODEM_FIRMWAR..."}
replace-the-affected-fwd-flight-computer["<small><b>Step 5</b></small><br/>Action: Replace the affected FWD Flight Compu..."]
replace-the-affected-aft-flight-computer["<small><b>Step 6</b></small><br/>Action: Replace the affected AFT Flight Compu..."]
did-this-resolve-the-issue{"<small><b>Step 7</b></small><br/>Question: Did this resolve the issue?"}
return-the-aircraft-to-service["<small><b>Step 8</b></small><br/>Action: The Aircraft may return to service."]
escalate-to-p2-embedded-linux{{"<small><b>Step 9</b></small><br/>Escalation: Escalate to P2 Embedded Linux On Call."}}
are-you-troubleshooting-an-ev2-or-ev3 -->|EV2| replace-the-affected-ev2-flight-compute
are-you-troubleshooting-an-ev2-or-ev3 -->|EV3| determine-the-affected-ev3-compute
replace-the-affected-ev2-flight-compute --> did-this-resolve-the-issue
determine-the-affected-ev3-compute --> which-ev3-compute-has-the-alarm
which-ev3-compute-has-the-alarm -->|/compute_a| replace-the-affected-fwd-flight-computer
which-ev3-compute-has-the-alarm -->|/compute_b| replace-the-affected-aft-flight-computer
replace-the-affected-fwd-flight-computer --> did-this-resolve-the-issue
replace-the-affected-aft-flight-computer --> did-this-resolve-the-issue
did-this-resolve-the-issue -->|Yes| return-the-aircraft-to-service
did-this-resolve-the-issue -->|No| escalate-to-p2-embedded-linux
style are-you-troubleshooting-an-ev2-or-ev3 fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style replace-the-affected-ev2-flight-compute fill:#dcfce7,stroke:#22c55e,color:#14532d
style determine-the-affected-ev3-compute fill:#dcfce7,stroke:#22c55e,color:#14532d
style which-ev3-compute-has-the-alarm fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style replace-the-affected-fwd-flight-computer fill:#dcfce7,stroke:#22c55e,color:#14532d
style replace-the-affected-aft-flight-computer fill:#dcfce7,stroke:#22c55e,color:#14532d
style did-this-resolve-the-issue fill:#dbeafe,stroke:#3b82f6,color:#1e3a5f
style return-the-aircraft-to-service fill:#dcfce7,stroke:#22c55e,color:#14532d
style escalate-to-p2-embedded-linux fill:#fef3c7,stroke:#f59e0b,color:#78350f Hover or focus a block to preview it. Select the block to keep the preview open.
1 question
Are you troubleshooting an EV2 or EV3 Aircraft?
2 action
Replace the affected Flight Compute Assembly. For steps, see:
1. UMM: Remove Flight Compute Assembly (FCA)
2. UMM: Install Flight Compute Assembly (FCA)
WORK ORDER TEMPLATE: Use the work order template that matches the hardware version:
- Work Order Template #27 - EV2: Replace Flight Compute Assembly
1. UMM: Remove Flight Compute Assembly (FCA)
2. UMM: Install Flight Compute Assembly (FCA)
WORK ORDER TEMPLATE: Use the work order template that matches the hardware version:
- Work Order Template #27 - EV2: Replace Flight Compute Assembly
3 action
4 question
Which compute has
CELL_MODEM_FIRMWARE_MISMATCH set? 5 action
Replace the affected FWD Flight Computer. For steps, see:
1. 42.1.1.e Remove Forward (FWD) Flight Computer (FC)
2. 42.1.1.f Install Forward (FWD) Flight Computer (FC)
WORK ORDER TEMPLATE: Use the work order template that matches the hardware version:
- Work Order Template #654 - EV3: Replace FWD Flight Computer
1. 42.1.1.e Remove Forward (FWD) Flight Computer (FC)
2. 42.1.1.f Install Forward (FWD) Flight Computer (FC)
WORK ORDER TEMPLATE: Use the work order template that matches the hardware version:
- Work Order Template #654 - EV3: Replace FWD Flight Computer
6 action
Replace the affected AFT Flight Computer. For steps, see:
1. 42.1.1.g Remove AFT Flight Computer (FC)
2. 42.1.1.h Install AFT Flight Computer (FC)
WORK ORDER TEMPLATE: Use the work order template that matches the hardware version:
- Work Order Template #1052 - EV3: Replace AFT Flight Computer
1. 42.1.1.g Remove AFT Flight Computer (FC)
2. 42.1.1.h Install AFT Flight Computer (FC)
WORK ORDER TEMPLATE: Use the work order template that matches the hardware version:
- Work Order Template #1052 - EV3: Replace AFT Flight Computer
7 question
Did this resolve the issue?
8 action
The Aircraft may return to service.
9 escalation
Escalate to P2 Embedded Linux 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:
Session is too large to fit in a URL. Use Download session JSON to share the timeline out-of-band.
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