Rule 116 EPC is Not a Safe Harbour: T 1731/23 on Late-Filed Requests
The Board of Appeal in T 1731/23 confirms that filing an auxiliary request before the Rule 116 EPC deadline does not guarantee its admittance. Opposition divisions retain full discretion over late-filed amendments.
There is no established principle that submissions filed before the Rule 116 EPC deadline are generally admissible, just as there is no rule rendering submissions filed after that date automatically inadmissible. In T 1731/23, Technical Board of Appeal 3.5.01 dismantled the assumption that meeting a procedural deadline strips the opposition division of its discretion to reject late-filed amendments.
The adjourned oral proceedings
The procedural dispute arose from a bifurcated hearing. During the first oral proceedings on 17 May 2023, the proprietor filed an auxiliary request to address clarity and Rule 80 EPC issues. Lacking time to discuss it, the opposition division adjourned the hearing to 15 June 2023. The new summons retained the original final date for written submissions: 17 March 2023.
One day before the second leg of the hearing, the proprietor filed a new auxiliary request, replacing a feature regarding grid codes with a new feature extracted from the description concerning individual wind turbine controllers. The opposition division refused to admit it.
On appeal, the proprietor argued that the opposition division had failed to set a valid final date for the adjourned proceedings. Furthermore, they relied on case law suggesting that requests filed before a Rule 116 EPC deadline expires are generally admissible, arguing this principle should extend to features taken from the description.
The myth of the deadline safe harbor
The Board rejected this procedural theory entirely. Addressing the calendar issue first, the panel noted that while adjourning oral proceedings requires a new summons, it does not require a new final date for submissions if the subject of the proceedings remains unchanged (reasons 14).
More fundamentally, the Board clarified the nature of the deadline itself. The panel held that there is no established principle that submissions filed before the date set under Rule 116 EPC are generally admissible (reasons 12). The opposition division retains discretion over amendments filed after the period specified in the initial communication under Rule 79 EPC.
The opposition division had exercised this discretion reasonably. The amendment was filed one day before the hearing, introduced a complex feature from the description that would require an additional prior art search, and represented a divergent shift in the claimed subject matter (reasons 13).
Simulating the wind farm
With the late requests excluded, the substantive debate centered on inventive step. The patent claimed a simulator for testing a wind farm controller without connecting it to a real wind farm. The processing unit calculated electrical parameter values based on input data and a network model, transmitting the output back to the controller so it operated as if connected to a real grid.
The prior art, D2, disclosed a real-time simulator for grid-connected wind farms using hardware-in-the-loop (HIL) simulation to test digital controllers. The proprietor argued that D2's "digital controller" was not specifically a wind farm controller. The Board disagreed, noting that a controller tested in this environment must influence and be influenced by the wind farm to be meaningful (reasons 4).
Formulating the objective technical problem as how to test a wind farm controller without connecting it to a real wind farm, the Board found the solution obvious. Because D2 disclosed HIL simulation, which inherently requires a closed control loop, the skilled person would inevitably feed the output values back to the controller (reasons 7). Further auxiliary requests adding requirements to verify grid code compliance or individually virtualise turbines were similarly dismissed as obvious implementations of realistic testing conditions already envisaged by D2 (reasons 23, 32).
Practical implications
This decision serves as a critical procedural warning regarding adjourned oral proceedings. If a hearing is split, do not assume the clock resets for filing new requests. Unless the substantive focus of the proceedings has shifted, the original Rule 116 EPC deadline continues to govern.
Furthermore, practitioners must treat the final date for written submissions as a procedural cutoff, not an admissibility guarantee. Extracting untested features from the description late in the opposition proceedings remains highly risky, regardless of whether the Rule 116 EPC deadline has technically expired. The opposition division's discretion to reject complex, non-convergent amendments remains fully intact.
Sources
Further Reading
Articles related to the topics covered above.
Arbitrary Modifications and Late Submissions: T 0094/24 on the Problem-Solution Framework
Board 3.5.05 confirms that features failing to credibly achieve a technical effect over the whole claimed scope are arbitrary modifications, requiring no objective technical problem to be formulated.
The Limits of G 2/21: T 0655/24 on Post-Published Evidence and Improved Effects
Board 3.3.04 rejects recent case law allowing post-published evidence to prove an improved effect, holding that improvements must be credible from the application as filed.
The Substantiation Threshold: T 0241/25 on Intermediate Generalisations
Board 3.2.02 establishes a strict pleading standard for added matter objections. Merely pointing to an embodiment and asserting an intermediate generalisation is legally insufficient without explaining the inextricable link.