Overview
A little box installed to help troubleshoot flap failures is now being treated like a saboteur. As of December 23, 2025, the FAA says Challenger 604 operators must disconnect the flap system on-board recorder (FSOBR) if it’s installed—and they’re banned from putting it back.
The hook is uncomfortable: this isn’t a cracked bracket or a leaky seal. It’s an optional “diagnostics” add-on that can interfere with flap-control signals, trip monitors, throw “Flap Fail” messages, and—under the wrong combination of failures—push toward uncommanded flap movement and loss-of-control risk.
Key Indicators
People Involved
Organizations Involved
The FAA turned a foreign-identified design risk into a binding U.S. maintenance order for Challenger 604 operators.
Transport Canada is the State of Design authority whose directive set the technical narrative and the fix.
Bombardier supplies the service-bulletin playbook regulators point to when they order changes.
EASA’s AD portal is where international operators often first see foreign directives propagate.
Boeing appears here as a commenter pushing for clarity, not as the affected manufacturer.
Timeline
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The order becomes real: disconnect by the clock
ComplianceAD 2025-22-04 becomes effective; installation or reconnection is now prohibited in the U.S.
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FAA finalizes AD 2025-22-04
Rule/RegulatoryThe FAA adopts the final rule, citing risks of flap failures and uncommanded flap movement tied to FSOBR interference.
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FAA proposes mirroring Canada’s fix in the U.S.
RulemakingThe FAA publishes an NPRM proposing mandatory FSOBR disconnection and a prohibition on future installation.
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Canada revises and clarifies: CF-2024-31R1
Rule/RegulatoryTransport Canada revises the directive, keeping the disconnect-and-ban remedy while clarifying applicability details.
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Canada fires the first shot: AD CF-2024-31
Rule/RegulatoryTransport Canada issues an airworthiness directive targeting FSOBR-related effects on flap control.
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Bombardier publishes the “disconnect it” playbook
MaintenanceBombardier issues service bulletins that define procedures to disconnect the FSOBR on affected aircraft.
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FSOBR arrives as an optional flap “black box”
Product/EngineeringBombardier introduces FSOBR as an option to help troubleshoot flap system failures.
Scenarios
“FSOBR Quietly Disappears From the Fleet”
Discussed by: FAA and Transport Canada through the final rule and the originating Canadian AD
Most operators treat this like a low-drama maintenance action: schedule the disconnect during routine downtime, log compliance, and move on. The key trigger is simply calendar and utilization—high-hour aircraft hit the 1,000-hour threshold quickly, while low-utilization jets comply at the 14-month mark. The long-term effect is cultural as much as technical: optional “helpful” recorders that touch flight-control signals become harder to justify without stronger isolation and certification guardrails.
“Operators Push for an AMOC or a Safer Replacement Recorder”
Discussed by: FAA framework for Alternative Methods of Compliance (AMOCs) described in the AD; operator and MRO compliance planning
Some operators will want the troubleshooting benefit back, especially for stubborn intermittent flap faults. The trigger is operational pain: repeated flap-related writeups with no easy root cause once FSOBR is gone. That pressure can lead to AMOC requests or a redesigned recorder pathway that doesn’t interface with sensitive I/O signals. If a replacement emerges, the story shifts from “disconnect” to “disconnect, then retrofit something safer.”
“More Flap-System Actions Follow After New Incident Data”
Discussed by: Regulatory logic described in the FAA preamble: incident reporting, bilateral data-sharing, and SDR availability
If flap-control incidents continue after the FSOBR failure mode is removed, regulators may conclude the recorder wasn’t the whole story—just the easiest lever to pull first. The trigger would be a cluster of post-compliance events pointing to other weak links (wiring, control unit monitoring behavior, or combined-failure pathways). That would produce follow-on service bulletins, expanded inspections, or additional ADs that go deeper than simply disconnecting a device.
Historical Context
Boeing 737 MAX MCAS Crisis (Flight-Control Logic + Sensor Inputs)
2018-10 to 2020-11What Happened
A flight-control augmentation function repeatedly pushed the nose down when fed faulty sensor data, contributing to two fatal crashes and a global grounding. The technical storyline became a governance storyline: how software, sensors, certification, and training intersect.
Outcome
Short term: The fleet was grounded and later returned after design, training, and oversight changes.
Long term: Regulators and industry became far more suspicious of hidden coupling in control systems.
Why It's Relevant
This Challenger story rhymes because the risk isn’t “the part breaks,” it’s “the signals get weird,” and weird signals can become loss-of-control scenarios fast.
Airworthiness Directives as “Fleetwide Hotfixes” for Systemic Design Risks
1970s–presentWhat Happened
Across decades, regulators have repeatedly used ADs to force rapid, standardized changes—especially when an unsafe condition can appear across an entire type design. The remedy is often pragmatic: disable, inspect, or limit operation while engineering catches up.
Outcome
Short term: Operators comply through maintenance actions tied to time, cycles, or hours.
Long term: Design practices evolve to reduce unintended interactions and improve fault isolation.
Why It's Relevant
The FSOBR action is a classic “disable the coupling” hotfix: cheap, fast, and enforceable.
Aging Aircraft Avionics Add-Ons Become Liability Over Time
1990s–presentWhat Happened
Aftermarket or optional avionics additions often start as improvements, then become compatibility headaches as fleets age, wiring changes, and failure combinations multiply. Regulators typically respond when incident data reveals an interaction nobody modeled upfront.
Outcome
Short term: Targeted removals/disconnects and installation prohibitions stabilize risk.
Long term: Standards and certification expectations tighten around integration and interference.
Why It's Relevant
FSOBR was introduced as a helpful option; a decade later it’s being treated as an integration risk.