Evidence - General. Canada (Transportation Safety Board) v. Carroll‑Byrne
In Canada (Transportation Safety Board) v. Carroll‑Byrne (SCC, 2022) the Supreme Court of Canada considered the disclosure of a cockpit voice recorder (CVR) in the course of civil class litigation regarding an airplane crash. The disclosure of the CVR - as an "on‑board recording" - was governed by the Canadian Transportation Accident Investigation and Safety Board Act (CTAISBA). The case thus involves a balancing between the presumed evidentiary search for the truth on the one hand, and the specific statutory (and discretionary) privilege of the CTAISBA.
Here the court considers the very basic public interest purpose evidence-gathering, in contrast to a specific statutory privilege:
 What Parliament has designated as the public interest in the proper administration of justice concerns a party’s right to a fair trial and to present all relevant evidence that is necessary to resolve the dispute (see Dubin Report, at p. 234; International Civil Aviation Organization, Manual on Protection of Safety Information, Part I — Protection of Accident and Incident Investigation Records, Doc. 10053 (1st ed. 2016), s. 188.8.131.52; Hyde Park, at para. 74; Air France, at paras. 121 and 138). At its core, this relates to the question of whether withholding evidence would interfere with the fact‑finding process to such an extent that it would undermine a party’s right to a fair trial and, consequently, public confidence in the administration of justice. But relevancy and trustworthiness are not absolute values; the very existence of the privilege suggests that Parliament is prepared to subordinate the truth‑finding function of a civil trial to what it sees as potentially higher values.. Girao v. Cunningham
 I note, without commenting further, that the nature of the proceeding may be relevant to the final balancing, in that criminal or disciplinary proceedings may engage different interests (see, e.g., Dubin Report, at pp. 234‑35, which stated that the considerations that apply to criminal and disciplinary cases may differ from civil proceedings). There are also additional procedural protections that limit the use of CVR evidence, including a firm prohibition on the use of CVRs in disciplinary proceedings against pilots or proceedings related to the competency of pilots, in addition to other legal proceedings involving, in particular, air traffic controllers (s. 28(7)). The chambers judge did not lose sight of this, recalling the prohibition in s. 28(7) explicitly in making his order (para. 69).
 The ultimate balancing requires the court or coroner to identify the relevant factors and decide whether, in light of all of the circumstances, the public interest in the administration of justice commands production and discovery of the CVR, notwithstanding the weight accorded to the privilege by Parliament. When measuring the public interest in the administration of justice, the decision-maker should consider the recording’s relevance, probative value and necessity to resolving the issues in dispute as factors that point to the importance of the recording to a fair trial. On the privilege side of the scale, the decision-maker should consider the effect of release on pilot privacy and on transportation safety, as fostered by free communications in the cockpit. Air France and Hyde Park correctly identified most of these factors as relevant to the balancing exercise.
 All parties recognize that the test for production is not a simple relevance test. Care should be taken to not order production merely because the CVR would be helpful and provide complete evidence, something that Gauthier J. in Hyde Park rightly brought to light (para. 74). As the ACPA notes, testimony from the pilots will often have gaps. That is the nature of memory and live testimony. A court must consider not only the existence or number of gaps in the evidence but also the significance of the gaps in relation to the facts and legal issues in dispute. Other ways of filling gaps, including by refreshing pilots’ memory using the Board’s report or through witness statements, should also be considered (see Laporte Affidavit, A.R., at p. 1877, para. 99). A party seeking to set aside the statutory privilege must undertake reasonable measures to obtain the necessary information from other non‑privileged sources. A similar idea is expressed in the journalistic source privilege: disclosure is only possible where the “information or document cannot be produced in evidence by any other reasonable means” (CEA, s. 39.1(7)(a); see also National Post, at para. 66, on the “alternate sources” principle).
The case of Girao v. Cunningham (Ont CA, 2020) is a remarkable ruling. That it had to be written this way is an embarrassment to the legal profession. It should be read by any litigation lawyer, especially those practicing MVA litigation, as a salutory lesson in dealing with self-representing parties. On it's face it was an appeal of an MVA tort jury award, but the Court of Appeal took the oppourtunity to review numerous (sadly, necessary) basics of civil litigation. Dealing at trial with a self-represented plaintiff who relied on a Spanish interpreter throughout, the Court of Appeal used defence behaviour as object lessons in why these legal principles are important and in the end, took the unusual step of ordering a new trial from scratch [paras 7, 173-174].
I'll go through the legal principles one by one as per topic, here evidence law basics:
 It is trite law that evidence is admissible if it is relevant to a fact in issue in the case and is not subject to an exclusionary rule. The trial judge also has discretion to refuse to admit evidence where its prejudicial effect would exceed its probative value: Draper v. Jacklyn (1969), 1969 CanLII 6 (SCC),  S.C.R. 92. That case involved graphic photographs of a motorist’s injuries that were admitted at trial. While holding that the photographs were properly admitted, Spence J. said at p. 98:. R v Vassel
The occasions are frequent upon which a judge trying a case with the assistance of a jury is called upon to determine whether or not a piece of evidence technically admissible may be so prejudicial to the opposite side that any probative value is overcome by the possible prejudice and that therefore he should exclude the production of the particular piece of evidence. This principle applies generally and beyond physical evidence along with the trial judge’s residual discretion to exclude evidence. See R. v. Lyttle, 2004 SCC 5,  1 S.C.R. 193, at para. 44; R. v. Meddoui, 1991 CanLII 42 (SCC),  3 S.C.R. 320, at para. 3; and Bruff-Murphy v. Gunawardena, 2017 ONCA 502, 138 O.R. (3d) 584, at paras. 29-32.
In R v Vassel (Ont CA, 2018) the Court of Appeal provides a definition of admissibility:
 Admissibility. Relevant and material evidence is admissible if it satisfies all the existing tests and extrinsic policies of the law of evidence, whether based on common law principles, statutory provisions or constitutional precepts: Luciano, at para. 209; R. v. Zeolkowski, 1989 CanLII 72 (SCC),  1 S.C.R. 1378, at p. 1386. . R v Ansari
In R v Ansari (Ont CA, 2015) Watt JA usefully stated some basic principles of evidence law and their inter-relation [respecting relevance, admissibility, prejudice and whether evidence is probative]:
 The resolution of this ground of appeal requires consideration and application of fundamental principles of the law of evidence. First, the notion of relevance. And, second, the admissibility rule that excludes relevant and material evidence on the ground that its probative value is exceeded by its prejudicial effect.
 Relevance is not an inherent characteristic of any item of evidence. Relevance exists as a relation between, on the one hand, an item of evidence and, on the other, a proposition of fact that the evidence is offered to prove. Relevance is a matter of everyday experience and common sense. An item of evidence is relevant if, by the application of everyday experience and common sense, it renders the fact it seeks to establish by its introduction slightly more or less probable than the fact would be without it: R. v. Luciano, 2011 ONCA 89 (CanLII), 267 C.C.C. (3d) 16, at para. 204.
 Relevance does not exist in the abstract or in the air: Cloutier v. The Queen, 1979 CanLII 25 (SCC),  2 S.C.R. 709, at pp. 730-732; Luciano, at para. 205. Relevance is also relative; we assess and determine it in the context of the entire case in which the evidence is proffered and the positions of counsel in that case: Cloutier, at pp. 730-732; and Luciano, at para. 205.
 To be relevant, an item of evidence need not prove conclusively the proposition of fact for which it is introduced. Nor does the evidence, to be relevant, need to make the proposition of fact more probable than not. An item of evidence is not irrelevant simply because it can sustain more than one inference. The requirement of relevance is met where the item of evidence reasonably shows, “by the application of everyday experience and common sense[,] that the fact is slightly more probable with the evidence than it would be without it”: Luciano, at para. 206.
 Admissibility is a legal concept. Admissibility rules exclude evidence that is both relevant and material on the basis of some policy consideration that the law regards as of sufficient importance to warrant exclusion of evidence that would otherwise assist the trier of fact in ascertaining the truth of the matter at hand. The rule that excludes relevant and material evidence on the basis that its probative value is outweighed by its prejudicial effect is a rule of admissibility.
 The prejudice component of this general exclusionary discretion may involve either or both of two types of prejudice.
 Moral prejudice refers to the risk of an unfocused trial and a conclusion of guilt based on a prohibited chain of reasoning from a general disposition or propensity to guilt of the offence charged. In other words, a finding of guilt that is based on character, not conduct: R. v. Handy, 2002 SCC 56 (CanLII),  2 S.C.R. 908, at paras. 31 and 139.
 Reasoning prejudice involves the distraction of the trier of fact from their proper focus on the offence charged by the introduction of evidence of other incidents that consume undue time and may be accorded more weight than should be their due: Handy, at para. 31 and 144.
 When invited to exclude relevant, material and otherwise admissible evidence on the basis that its prejudicial effect predominates over its probative value, a trial judge will consider the individual constituents of the rule – probative value and prejudicial effect – and then balance them to determine which predominates.
 The assessment of probative value involves consideration of the strength of the evidence; the extent to which it supports the inferences the proponent seeks to have drawn from it; and the extent to which the matters the evidence tends to prove are at issue in the proceedings: R. v. B. (L.); R. v. G. (M.A.) (1997), 1997 CanLII 3187 (ON CA), 116 C.C.C. (3d) 481 (Ont. C.A.), at para. 23.
 An assessment of prejudicial effect should take into account:
i. the degree of discreditable conduct disclosed by the evidence; A trial judge’s decision about where the balance settles between probative value on the one hand and prejudicial effect on the other is accorded a high degree of deference by appellate courts. Where a trial judge has applied the proper principles, weighed the probative value of the evidence and its potential prejudice and decided the issue of admissibility, appellate courts will not lightly intervene: R. v. Arp, 1998 CanLII 769 (SCC),  3 S.C.R. 339, at para. 42; R. v. Bevan, 1993 CanLII 101 (SCC),  2 S.C.R. 599, at p. 613; R. v. B. (C.R.), 1990 CanLII 142 (SCC),  1 S.C.R. 717, at pp. 733-734; R. v. Samuels, 2013 ONCA 551 (CanLII), 310 O.A.C. 175, at para. 47; B. (L.); G. (M.A.), at para. 51.
ii. the extent to which the proposed evidence may support an inference of guilt on the sole basis of bad character;
iii. the extent to which the evidence may confuse issues; and
iv. the ability of the accused to respond to the evidence.
B. (L.); G. (M.A.), at para. 24.
 A final point concerns prophylactic measures undertaken by the trial judge to reduce the risk of reasoning or moral prejudice. A limiting instruction that explains the proper use of this evidence and enjoins prohibited reasoning is of critical importance in ensuring a fair trial: R. v. Vukelich (1996), 1996 CanLII 1005 (BC CA), 108 C.C.C. (3d) 193 (B.C. C.A.), at para. 51.