What information aviation experts should be allowed to rely upon in formulating opinions for trial

In a previous article, we discussed the hearsay issues contained in NTSB reports, which can be challenged as inadmissible evidence in court. However, the general rule regarding experts in aviation cases allows such experts to base their opinions on certain inadmissible evidence, so long as the information is “reasonable to rely upon” and has more “probative value” than prejudicial effect.[1] Thus, it is often difficult to exclude an expert’s testimony based on hearsay evidence. The use of an expert to “bring in” normally inadmissible evidence is sometimes characterized as a “back door” to the hearsay rule.

However, under the clear language of 49 U.S.C. §1154(b) regarding NTSB reports, there is a strong basis for excluding experts’ opinions that are based on such hearsay evidence. The New Jersey District Court in Credle v. Smith & Smith, Inc.[2] specifically addressed this issue and ruled in that case that the expert opinions based on the inadmissible evidence from the NTSB report was also to be excluded – it prohibited the plaintiffs’ expert from referring to or even mentioning the facts or conclusions as determined by the NTSB.

Similarly, a federal district court in Georgia actually struck portions of a plaintiffs’ complaint (upon which the expert was going to rely) that were based on the NTSB probable cause determinations.[3] The plaintiffs in the Knous v. U.S. case alleged, “[t]he NTSB investigation found, in part, that the air traffic controllers’ failure to report precipitation information was a cause of the accident.” Even though they agreed to strike the probable cause determination, the plaintiffs’ attorneys sought leave to reword the remaining NTSB allegations without mentioning the NTSB by name – the Court rejected this request because the allegations impermissibly drew from the NTSB accident report.

Still, many other courts allow experts to rely on inadmissible evidence that they may have reviewed in the NTSB report to formulate their opinions and testify to them in court. This “back door” to the hearsay rule provides unique challenges to attorneys seeking to use or exclude certain experts from the case. Here are some of the key considerations we often explore in our aviation cases:

Tests and information “reasonably relied upon” by experts in the field.

One of the key considerations as to whether an expert can testify about hearsay evidence is whether the facts or tests that form the basis of the experts’ opinions are such that generally experts in the field would normally “reasonably rely upon.” Under the N.C. and Federal evidence rules, an expert may even properly base his or her opinion on tests performed by another person, if the tests are of the type reasonably relied upon by experts in the field.[4] The Courts have held that expert witnesses may rely on data and other information supplied by third parties even if the data were prepared for litigation by an interested party. Unless the expert’s opinion is too speculative, it should not be rejected as unreliable merely because the expert relied on the reports of others.[5]

For example, in criminal matters, the N.C. court allowed an expert to state medical opinions based on the contents of another doctor’s medical report and information supplied to the witnesses.[6] The medical report and information was the type that such experts generally used in the field (per testimony) and thus, the Court did not deem the evidence inadmissible simply because it contained hearsay from the doctor, who did not testify in court. This same rule of evidence would apply to civil cases as well. 

Thus, one of the lines of questions that is important to explore in any aviation accident case is whether the tests and data relied upon by the experts are the type reasonably relied upon by experts in that field. Sometimes, a particular test may not be considered authoritative (i.e. “junk science”) in the field, but an expert might rely on it because it helps to bolster her/his opinion on an issue—and indeed, the acceptable scientific methodology may change overtime as the field becomes more sophisticated. Thus, reliance on a test that uses an older methodology that has been challenged or debunked could be the basis for excluding an expert’s opinion. The only way to know this information is to have an expert (consulting or testifying) in your own corner evaluating the bases of the opinions of the other expert.

Expert cannot merely “parrot” the opinions of other non-testifying experts.

Importantly, the expert must present her/his own independent analysis and not merely “parrot the opinions of others.”[7]While an expert’s opinion can properly be based on the out-of-court opinion of a non-testifying expert, there still must be some evidence of independent analysis.

For example, we would argue that an accident reconstructionist in an aviation case could not simply rely upon an NTSB’s toxicologist evaluation of prescription medications to conclude that a pilot was intoxicated at the time of the accident (i.e. simply “parroting” the hearsay testimony of another expert from the NTSB report); rather, a separate toxicologist would still be required to interpret the tests and facts in the NTSB report, to form the basis of such opinion, and to then testify as to intoxication. Then, such expert opinion would likely be admissible in court.

An expert’s opinion may also be excluded where an expert witness seeks to testify that the opinion of a non-testifying expert was the same as, consistent with, or agreed with her/his own opinion, without also testifying that in reaching that opinion the witness relied, partially, upon the opinion of the non-testifying expert. In the U.S. v. Tran Trong Cuong case, a doctor was being prosecuted for illegally dispensing drugs. A medical expert presented by the prosecution testified that his opinions concerning defendant’s activities were “essentially the same” as those of a Dr. Stevenson, who did not testify.[8] The court, reversing a conviction, held that this testimony was excludable hearsay and prejudicial to the defendant. It is error to allow an expert witness to “bolster,” or “corroborate,” her/his opinion by informing the jury that other experts agree with him, unless the witness also testifies she/he has relied, in part, on the opinions of the other experts in forming his own opinion.[9]

Learned Treatises- N.C. Evidence R. 803 (18)

Another exception to the hearsay rule is the “Learned Treatises” exception. Certain studies are admissible when they are called to the attention of an expert witness on cross-examination or relied upon in direct examination, and are contained in published treatises, periodicals, or pamphlets on a subject of history, medicine, or other science or art, established as a reliable authority. These factors are usually provided by the testimony or admission of the witness, by other expert testimony or by judicial notice. 

For example, aviation experts can rely upon well-known and accepted journals and publications in the industry, if they are considered reliable in the field. Accordingly, we often request in our standard expert discovery requests a list of all publications that the purported expert has been published in and then we can ask, in deposition, which publications she/he finds authoritative in the field. Presumably, if the expert has been published in a particular journal, she/he is likely to find it authoritative and articles that contradict or challenge the bases for her/his opinions from that same journal or periodical can then be used as cross-examination potential.

Probative value must substantially outweigh prejudicial value.

Under N.C. and Federal Rule 703, the trial court must balance the probative value of the facts, data, or opinions in assisting the jury to evaluate the expert’s opinion on the one hand, against the risk of prejudice resulting from the jury’s potential misuse of the facts, data, or opinions for substantive purposes on the other hand. 

Information may be disclosed to the jury by the proponent of an opinion only if the trial court finds that the probative value of the information substantially outweighs its prejudicial effect.[10] In fact, the court is required to give a limiting instruction, upon request, informing the jury that the underlying facts, data, or opinions must not be used for substantive purposes.

For all practical purposes, however, it is very hard to “un-ring the bell” once the jury has heard about some evidence that an expert relied upon in formulating an opinion, even if it should not be considered “substantive.” An expert is entitled to make certain assumptions and explain to the jury what those assumptions were. The opposing party is then allowed to challenge the reliability or weight of the expert’s opinion by arguing that there is no evidence presented to prove the assumption, upon which such expert relied. 

However, the courts recognize that there is a limit to the jury’s ability to distinguish between substantive evidence and the assumption an expert might rely upon in formulating an opinion. Upon the proper objection by legal counsel, it is possible to challenge or limit the testimony of an expert. At least, the court should prohibit an expert from merely “parroting” the opinions of other non-testifying experts or the court may instruct an expert to refrain from discussing certain assumptions that are not proven or offered into evidence, on the basis that such would cause more confusion and jury misuse than provide the appropriate probative value.

Should you have any questions about the admissibility of a particular expert opinion, please contact the CSH Law Aviation Practice Group.


[1] Federal Rule Evidence 703; N.C. Rule Evidence 703 (If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence.); State v. Fair, 354 N.C. 131, 557 S.E.2d 500 (2001).

[2] Credle v. Smith & Smith, Inc.,42 F.Supp. 3d. 596 (D.N.J. 2013).

[3] Knous v. United States, 981 F. Supp. 2d 1365 (N.D. Ga. 2013).

[4] State v. Fair, 354 N.C. 131, 557 S.E.2d 500 (2001); State v. Thompson, 188 N.C. App. 102, 654 S.E.2d 814 (2008), review denied, 662 S.E.2d 391 (N.C. 2008); State v. Durham, 176 N.C. App. 239, 625 S.E.2d 831 (2006); State v. Mobley, 684 S.E.2d 508 (N.C. Ct. App. 2009).

[5] N.C. R. Evid. 702(a)(1). State v. Denton, 829 S.E.2d 674 (N.C. Ct. App. 2019).

[6] State v. Smith, 315 N.C. 76, 337 S.E.2d 833 (1985)

[7] In re A.N.B., 754 S.E.2d 442, 449 (N.C. Ct. App. 2014) (Where a licensed professional counselor both reviewed other clinicians’ records and personally assessed the mental health patient, a sufficient basis was in evidence to render an expert opinion as to the mental state and needs of the patient in a commitment proceeding.)

[8] U.S. v. Tran Trong Cuong, 18 F.3d 1132, 1143-44, 40 Fed. R. Evid. Serv. 574 (4th Cir. 1994)

[9] See Todd v. Edwin L. Williams, II, M.D., Ltd., 242 Va. 178, 409 S.E.2d 450, 451-53 (1991); See also Hutchinson v. Groskin, 927 F.2d 722, 32 Fed. R. Evid. Serv. 628 (2d Cir. 1991).

[10]Fiorentino v. Rio Mar Associates, LP, SE, 381 F. Supp. 2d 43, 48 (D.P.R. 2005) (“Although undisputed that an expert may base his or her testimony on inadmissible facts or data, Rule 703 ‘does not allow the data itself.’ Bado–Santana v. Ford Motor Co., 364 F.Supp.2d 79, 91–92 (D.P.R.2005) (citing Engebretsen v. Fairchild Aircraft Corp., 21 F.3d 721, 728–729 (6th Cir.1994)) (holding that experts may rely on inadmissible material in forming the basis of opinions, but inadmissible material may not be admitted for truth of the matter asserted.)