Challenging a VIAC-appointed expert: raise bias within 15 days

An expert appointed by an arbitral tribunal may be challenged under Article 23 of the Vienna Rules where specific circumstances give rise to justifiable doubts about the expert’s impartiality or independence. The challenge must be made within 15 days after the party becomes aware of the ground and must state the ground together with supporting materials.

The rule concerns the person of the tribunal-appointed expert and any agreed qualifications. It addresses a different question from a technical objection to the data, method or calculations in the expert report. The relevant starting point is when the party learns of the ground for the challenge.

A party assessing a challenge should therefore record the date of knowledge, describe the specific circumstance and organise the documents supporting it. The arbitral tribunal decides the challenge.

What Article 23 of the Vienna Rules allows

Article 23 of the Vienna Rules concerns a challenge to an expert appointed by the arbitral tribunal. It makes Article 20 paragraphs 1 and 2 applicable by analogy. The relevant circumstances are therefore facts giving rise to justifiable doubts about the expert’s impartiality or independence. An agreed qualification may also matter where the expert does not meet it.

The rule provides a formal procedural route for person-related concerns. It does not replace a technical review of the expert report. Questions about the correctness of a calculation, the sufficiency of a data source or the reliability of a method belong to a separate technical submission.

Which facts may support a challenge

A party should describe the possible conflict as a verifiable fact. Depending on the circumstances, a close connection with a party, prior work for a person involved in the case or other concrete conduct may raise a concern about the required distance. Each situation requires its own assessment. A previous professional contact does not automatically establish a ground for challenge.

The key question is which specific fact affects impartiality, independence or an agreed qualification. Calling an expert biased does not answer that question. Keep the observed circumstance, its source and the resulting concern separate in the presentation.

When the 15-day period starts

Under Article 20 paragraph 2, which applies by analogy through Article 23, the challenge must be submitted within 15 days from the date on which the party became aware of the ground. The date of appointment is therefore not automatically the starting point. The report’s delivery matters only if the relevant circumstance became known through the report or its attachments.

Record the event that brought the ground to your attention. It may be a procedural communication, an attachment, a public statement or another item in the proceedings. Note when and through which document the connection became apparent. This chronology helps explain both the time limit and the basis of the challenge.

How to state and support the challenge

Article 20 paragraph 2 requires the challenge to specify its grounds and include corroborating materials. The submission should connect the expert, the specific circumstance, the date of knowledge and the resulting concern. A structured presentation helps the tribunal assess the issue and keeps the decisive document visible among the surrounding correspondence.

Preparation normally includes the appointment notice, relevant procedural orders, the source of the ground and proof of when that information became available. State facts and conclusions separately. Include points that can be followed from the attached documents or from a clear explanation of the event.

Who decides the expert challenge

Article 23 assigns the decision on the challenge to the arbitral tribunal. This differs from a challenge to an arbitrator, for which Article 20 itself provides a different decision-making route. The distinction should be reflected in the way the submission is framed.

Article 20 paragraph 2 refers to submission to the Secretariat for a challenge to an arbitrator. That requirement applies by analogy through Article 23, while Article 23 expressly assigns the decision on an expert challenge to the arbitral tribunal. The party should therefore follow the procedural order and communication channel of the pending VIAC arbitration. Timeliness, specific grounds and supporting materials remain central.

What effect the challenge has on the proceedings

Article 23 expressly refers to Article 20 paragraphs 1 and 2. It carries over the challenge standard and the 15-day and substantiation requirements. Article 20 paragraph 4 is not included in that reference. Article 23 therefore does not itself establish a general automatic stay of the arbitration.

If continued use of the expert or the report before the decision would create a procedural problem, the party should address that requested effect expressly. That request does not replace the formal grounds for challenge. The later assessment of the evidence remains a separate question from the expert’s personal impartiality.

Keep the formal challenge separate from technical criticism

A concern about the expert’s person relates to impartiality, independence or agreed qualifications. A technical objection concerns the assignment, data, method, calculation or conclusion in the report. Both questions may arise in the same arbitration, but they require different facts and requests.

The article on tribunal experts and counter-expertise addresses technical questioning and party experts under Section 601 ZPO. A challenge to an arbitrator is a separate Article 20 issue. Keeping these lines distinct prevents a technical disagreement from obscuring a time-sensitive person-related challenge.

Prepare the response within the period

First record the date of knowledge and place the 15-day period in the procedural calendar. Collect the appointment notice, relevant procedural orders and the document showing the possible conflict. State the ground as a sequence of concrete facts and match each important point with the appropriate supporting material.

Then check whether the concern really relates to the expert’s person. If the criticism concerns only the report, develop it as a technical submission. If both lines are present, keep them separate and make the formal challenge independently understandable within the time limit.

Questions about challenging a VIAC-appointed expert

Does the 15-day period always start with the expert’s appointment?

No. Article 20 paragraph 2, applied by analogy through Article 23, connects the period to the date on which the party became aware of the ground for challenge. Appointment and knowledge may coincide, but they do not have to.

Is it enough that I consider the expert’s method or result unconvincing?

A different technical assessment does not by itself establish a concern about impartiality or independence. Methodological objections and possible counter-expertise should be kept separate from the formal challenge of the expert.

Who decides the challenge to the tribunal-appointed expert?

Under Article 23, the arbitral tribunal decides the challenge to an expert appointed by the arbitral tribunal.

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Next step

Contract, arbitration clause, correspondence and deadlines should be collected. It can then be assessed whether negotiation, preservation or arbitration is central.