Accident Reconstruction Expert’s Opinion on Crew’s Inadequate Response Admitted
Posted on June 16, 2025 by Expert Witness Profiler
Plaintiff Sky Jet sought economic damages related to the destruction of the left engine of its 1996 Beech 1900D aircraft. Defendant VSE overhauled an engine part called a fuel control unit (“FCU”). Sky Jet claimed that the fuel control unit malfunctioned during two attempts to start to the aircraft, causing elevated internal engine temperatures, also referred to as “hot starts.”
Sky Jet sued VSE for negligence in its overhaul of the FCU. Defendant VSE has disclosed Mark Pottinger as its retained expert. Sky Jet filed a motion to exclude a causation opinion by Defendant’s expert Pottinger as unreliable and irrelevant.
Accident Reconstruction Expert Witness
Mark Pottinger is an aircraft accident investigation course graduate at the USC Viterbi School of Engineering and an affiliate member of the International Society Of Air Safety Investigators (ISASI).
He is an instructor at the Aviation Safety and Security Program of the Viterbi School Of Engineering. In 2013, Pottinger started his own consulting firm specializing in accident investigations and reconstructions. He develops trial exhibits for parties involved in complex aviation litigation. Pottinger also consults with clients who are or expect to be parties to litigation due to aircraft accidents or aviation activities.
Discussion by the Court
Mark Pottinger
Pottinger disclosed four reports. His initial report, dated November 15, 2023, explained that an “engine makes power by taking ambient air and drawing it through the inlet and into the compressor section of the engine,” before passing into a “single centrifugal impeller.” Pottinger also explained the role of pilots during starting procedures and the need for the pilot to “be vigilant for abnormal start conditions” and to “take immediate action to manage an abnormal start” at the risk of engine damage.
Pottinger reviewed the maintenance records for the engine. He noted that problems with the engine began a few weeks before the FCU was replaced.
Pottinger also inspected the engine. One of the straightening vanes was broken and cracked, and it had a broken weld on the top crossbar. Pottinger stated: “The impact of the broken straightening vane on engine operation, or what caused the damage to the vane, have not been determined.” However, he found that whatever the cause of the hot starts, the flight crew failed to appropriately react by aborting when the internal temperature reached 900 degrees. Both hot starts reached 1,000 degrees.
It should be noted that Pottinger supplemented his report three times. The last supplement, dated October 7, 2024, is at issue in the current motion. His specific opinion was that “[t]he fluctuating engine parameters and the poor starting performance of the subject engine resulted from the damaged diffuser straightening vane.”
Plaintiff filed a motion to exclude Pottinger’s opinion in his October 7 report that “a broken engine component called a ‘straightening vane’ caused ‘poor starting performance’ or ‘abnormal engine operation.'”
A. Undisclosed Opinions
Plaintiff’s first argument is that Pottinger should not be allowed to offer a previously undisclosed opinion that “the broken diffuser vane caused the hot start.” In response, Defendant stated that Pottinger never made such an assertion and will not testify to that effect at trial.
While this might appear to resolve the issue, Plaintiff, in its reply brief, accused Defendant of “playing semantic games,” arguing that Pottinger uses the terms “diffuser vane,” “straightening vane,” and “diffuser straightening vane” interchangeably—suggesting they refer to the same component. Plaintiff contends that Defendant is drawing an artificial distinction between these terms to claim that Pottinger never offered the disputed opinion. The Court observed, however, that Plaintiff’s own filings also use these terms inconsistently, making the distinction unclear on both sides.
The Court found the parties’ arguments on this issue confusing. Pottinger’s October 7 report does, in fact, contain an opinion about a “damaged diffuser straightening vane,” making it unclear what opinion Plaintiff believes was not disclosed.
As a result, the Court denied Plaintiff’s motion without prejudice. It emphasized that Pottinger’s opinions are documented in his report, and any testimony he offers at trial must align with what is stated there. However, due to the current lack of clarity in the record, the Court declined to make a definitive ruling on whether a specific opinion was disclosed or not. If necessary, Plaintiff may revisit the issue during trial.
B. Reliability
Pottinger’s October 7 report states that he had previously searched the Federal Aviation Administration’s Service Difficulty Report (“SDR”) system “for incidents that could be informative respecting the subject engine.” The two SDRs he discovered showed a damaged diffuser system causing increased temperatures and fluctuating engine parameters.
His specific opinion about the damaged diffuser straightening vane was based on the SDRs.
Plaintiff contended that “there is simply too great an analytical gap between Pottinger’s SDRs and any conclusion that the broken straightening vane caused hot starts.”
Plaintiff did not dispute that, in general, relying on SDRs is improper. Instead, Plaintiff argued that the SDRs cited by Pottinger involve situations too different from this case, creating an unacceptable gap in his reasoning.
The Court reviewed Pottinger’s reports along with the SDRs and agreed that there are some differences between those incidents and the present case. However, the Court finds that the gap in reasoning is not significant enough to make Pottinger’s opinions unreliable.
Service Difficulty Report
Plaintiff argues that the Service Difficulty Reports (SDRs) cited by Pottinger are not relevant for three reasons. First, the SDRs involved loose or broken diffuser tubes, whereas the engine in this case had a broken straightening vane. Based on this difference, Plaintiff claims the SDRs do not support the conclusion that a single broken straightening vane could affect engine performance.
The Court disagrees. As noted earlier, there is considerable confusion regarding the terminology and how these components relate to one another. In fact, Plaintiff’s own reply brief quotes Pottinger’s testimony, in which he suggests that diffuser tubes and straightening vanes function as part of the same system. This implies that Pottinger himself sees less of a distinction between the parts than Plaintiff claims.
Pottinger has also explained that both components work together to direct airflow into the engine, and that disrupting this airflow could adversely affect engine performance. Given this explanation, the Court finds that the fact the SDRs refer to diffuser tubes does not, by itself, make them irrelevant or render Pottinger’s opinion unreliable.
Plaintiff’s second and third objections are that neither of the SDRs involved a hot start or engine damage. But the Court found this unpersuasive. Just because the engine in this case was damaged by a hot start doesn’t mean the SDRs are irrelevant simply because they didn’t involve hot starts. Both SDRs describe abnormal engine behavior, which is central to Pottinger’s opinion.
The Court held that Pottinger’s reliance on SDRs where such irrevocable damage did not ultimately occur did not present so great an analytical leap—especially considering his emphasis on the crew’s inadequate response.
C. Relevance
Plaintiff’s third argument is that Pottinger’s October 7 report is not directly relevant to its claim that the fuel control unit (FCU) caused the hot starts. Plaintiff maintains that the central issue is whether the FCU was the cause and argues that Pottinger’s discussion of the diffuser or straightening vane has no bearing on that question.
However, the Court found that Plaintiff’s view of the issue is too narrow. While Plaintiff’s theory focuses on the FCU as the cause of the hot starts, the broader question in the case is what caused the engine damage. Plaintiff believes the FCU was to blame, but Defendant offers alternative explanations—including Pottinger’s opinion that other engine defects contributed and that the crew’s failure to respond appropriately was ultimately responsible.
Plaintiff also argued that Pottinger fails to connect his mention of “poor starting performance” to the hot start events. But this overlooked Pottinger’s opinion that the crew’s inadequate response played a key role in causing the damage.
In conclusion, the Court finds that Pottinger’s opinions are sufficiently relevant to the issues in the case.
Held
The Court denied the Plaintiff’s motion to exclude certain expert testimony of Mark Pottinger.
Key Takeaway:
Pottinger “carried out an extensive investigation,” including inspecting the engine and maintenance records. His findings were that the engine was having issues unrelated to the FCU. His examination of the engine found damage to the diffuser straightening vane and he proffered that the general rule is that the most “upstream” damage is usually a starting point for determining what went wrong.
He was able to rule out all potential causes except the broken diffuser straightening vane and pilot error. So although Pottinger ultimately relied on the SDRs, they were not the exclusive basis of his opinions. Pottinger also testified as to the distinctions between the SDRs and this case and explained why they were still persuasive.
Case Details:
| Case Caption: | Sky Jet M.G. Inc. V. VSE Aviation Services, LLC |
| Docket Number: | 2:23cv2210 |
| Court Name: | United States District Court, Kansas |
| Order Date: | June 13, 2025 |
