An informal arbitral award, being an expression of a negotiated resolution of the dispute referable to the will of the parties, may be challenged both for exceeding the limits of the mandate and for defects capable of vitiating the contractual will, such as duress, fraud, incapacity of the parties who conferred the mandate or of one of the arbitrators, and mistake.
In informal arbitration, the award may be challenged for essential mistake only where the formation of the arbitrators' will was deflected by an altered perception or a false representation of reality and of the factual elements submitted for their examination, and not where the deflection concerns the evaluation of a reality whose elements were correctly perceived.
An omission to adjudicate falls within the grounds that may in principle be raised when challenging an informal arbitral award, as it constitutes a breach of the mandate conferred upon the arbitrators.