FAA proposes AD for Challenger 600-series after flap malfunction risks 'loss of control'

Summary

The FAA has proposed a new airworthiness directive covering 610 US-registered Bombardier Challenger 600-series aircraft after a 2022 in-flight flap malfunction demonstrated that a single failed relay could allow uncommanded flap movement from 0 to 45 degrees — a condition the agency says could result in loss of control. The proposed AD, published May 26, 2026, targets Bombardier CL-600-1A11, CL-600-2A12, and CL-600-2B16 models and would require operators to revise aircraft flight manuals with crew procedures for runaway flap events.

The directive follows Transport Canada’s earlier action on the same risk. Comments on the proposed US rule are due July 10, 2026.

A latent relay failure that went undetected for at least 64 flights before triggering a full-flap runaway event has now produced a proposed US airworthiness directive with implications for every operator of a Bombardier Challenger 600-series business jet registered in the United States. The FAA published the proposal on May 26, 2026, citing a loss-of-control risk that regulators in both Canada and the UK have been tracking since a 2022 incident at Farnborough Airport.

The underlying event involved Challenger 604 registration D-AAAY, which experienced uncommanded flap movement during climb after departing Farnborough on August 10, 2022. The flap control system should have arrested movement at 3 degrees. Instead, a failed No. 1 flap retract relay allowed the flaps to travel from 0 to 45 degrees before the crew returned the aircraft to its departure airport without further incident.

The UK Air Accidents Investigation Branch later determined the relay failure had been latent across at least 64 prior flights — undetected, and silently defeating the system’s arrest logic each time.

Now the FAA is moving to close that gap for the US fleet. The proposed directive covers all Bombardier CL-600-1A11, CL-600-2A12, and CL-600-2B16 aircraft, encompassing the Challenger 600, 601, 601-3A, 601-3R, and 604 variants — a combined US-registered population of 610 aircraft.

What the proposed AD requires — and what it costs

The FAA’s proposed action is procedural rather than mechanical. Rather than mandating immediate hardware replacement or grounding, the directive would require operators to revise the aircraft flight manual (AFM) to provide crews with specific procedures for handling uncommanded, unarrested flap movement in flight. The FAA estimates compliance at $85 per aircraft, totaling $51,850 across the affected US fleet — a figure that covers the manual revision itself and does not account for operator-specific training or document-control overhead.

The proposal follows Transport Canada AD CF-2024-39, issued November 29, 2024, and a subsequent directive, CF-2025-51, effective October 22, 2025, which superseded an earlier 2023 Canadian rule and added functional tests of flap extension and retraction relays along with component life limits. Transport Canada, as the state of design authority for the Challenger family, has been the lead regulator on this issue; the FAA’s proposed rule aligns US requirements with the Canadian safety logic.

The full proposed directive is available through the Federal Register docket at the Department of Transportation, where operators can also submit comments before the July 10, 2026 deadline.

Why a procedural fix now — and what comes next

The FAA’s decision to lead with an AFM revision rather than a hardware mandate fits a recognizable regulatory pattern: when a latent failure mode is confirmed but the immediate risk can be mitigated through crew procedure, regulators typically establish the procedural floor first and layer in component-life requirements through subsequent directives. Transport Canada followed exactly that sequence — moving from a 2023 procedural directive to CF-2025-51’s functional tests and relay life limits within two years.

That trajectory matters for US operators. The current FAA proposal is the procedural floor, not the ceiling. Air Traveler Club’s coverage of the JetBlue A220 cockpit barrier exemption request illustrates how FAA rulemaking timelines can compress quickly when safety deadlines approach — operators who engage the comment process early tend to have more influence over compliance timelines and alternative means of compliance.

The broader signal here is about aging business-jet systems. A single latent relay failure — one component, undetected across 64 flights — produced a fleetwide unsafe condition across 610 aircraft. That is the kind of systemic vulnerability that regulators increasingly scrutinize as legacy cabin jets continue operating in high-cycle charter and owner-operator environments.

What the FAA timeline means for Challenger 600 operators

This is an awareness and early-action story: the proposed AD is not yet final, no aircraft are grounded, and the immediate compliance requirement — an AFM revision — is low-cost. But the comment deadline creates a real near-term window, and the regulatory trajectory from Canada suggests the final US rule may carry more weight than the proposal alone indicates.

• Submit comments before July 10, 2026: Operators with operational concerns, alternative compliance proposals, or data on relay failure rates should engage the FAA docket now. The Federal Register comment process is the only formal channel to influence the final rule’s scope or compliance timeline.
• Cross-check every tail against the three model codes: Verify each US-registered aircraft against CL-600-1A11, CL-600-2A12, and CL-600-2B16 designations. Do not assume variant-level exclusions without confirming against the actual Federal Register text.
• Circulate the proposed AFM procedure to flight crews immediately: Even before the final rule, flight departments should brief crews on the uncommanded flap movement scenario and the procedural response the FAA is proposing — the procedure itself reflects best practice regardless of rule status.
• Track Transport Canada CF-2025-51 as a forward signal: Canada’s directive already requires functional tests and relay life limits. If the FAA’s final rule incorporates similar hardware requirements, operators will need maintenance planning lead time beyond what the $85 AFM-revision estimate covers.

Watch for the FAA’s final rule publication following the July 10 comment close. If the agency moves from procedural mitigation to relay life limits or mandatory functional testing — mirroring Transport Canada’s CF-2025-51 — expect compliance costs and maintenance scheduling complexity to increase significantly across the affected fleet.

FAQ