Unlike many Part 135 operations, where overhaul intervals may be incorporated into approved maintenance programs, Part 91 operators generally are not required to overhaul an engine at the manufacturer’s recommended TBO. Nevertheless, after an accident, particularly one involving serious injuries or fatalities, operation beyond TBO can quickly become a focal point in the legal analysis.
The regulatory framework focuses on airworthiness rather than a specific overhaul interval. FAR 91.7(a) prohibits operation of an aircraft unless it is in an airworthy condition, while FAR 91.403 places primary responsibility for maintaining that condition on the owner or operator. As a result, an engine may legally exceed TBO and still remain airworthy if the aircraft conforms to its type design and remains in a condition for safe operation.
That legal distinction, however, often provides only limited protection once litigation begins. And the stakes increase dramatically when a fatality occurs. Plaintiffs will often argue that the operator accepted an unnecessary risk by continuing to fly an engine beyond the manufacturer's recommended overhaul interval. Such claims can be particularly significant when a person on the ground is injured or killed, as those third parties had no involvement in the flight and no opportunity to accept any aviation-related risks. Plaintiffs frequently contend that continued operation beyond the manufacturer's recommended service life created an unreasonable hazard to the public.
Investigators, insurers, and attorneys will closely examine the aircraft's maintenance history. Oil analysis reports, compression checks, borescope inspections, deferred maintenance items, logbook entries, and compliance with manufacturer service bulletins can become important evidence. Plaintiffs often emphasize that the operator disregarded guidance issued by the entity that designed and tested the engine. Although exceeding TBO does not violate Part 91 by itself, a jury could view the manufacturer's recommendation as evidence of prudent maintenance practice.
In many cases, litigation ultimately becomes a battle of experts. Plaintiffs will rely on experienced mechanics, engineers, accident reconstruction specialists, or manufacturer representatives who testify that TBO represents an important safety benchmark. Their argument is straightforward: the manufacturer recommended overhaul at a certain point, the operator chose not to follow that recommendation, and the accident occurred afterward.
The defense will generally respond that TBO is advisory—not mandatory—under Part 91. Defense experts will explain that engine condition is often more important than engine time and that many engines operate safely beyond TBO when supported by regular inspections, favorable oil analysis results, acceptable compression readings, and consistent maintenance. In essence, the defense seeks to shift the focus away from engine time viewed in a vacuum and toward engine condition, maintenance history and the operator’s decision making.
Both positions have support within the aviation community.
The challenge for aircraft owners is that the ultimate decision is rarely made by pilots, mechanics, FAA inspectors, or engineers. Instead, it is often made by a jury with little aviation background. Jurors must evaluate competing expert opinions and decide whether the operator acted reasonably under the circumstances. One expert may characterize operation beyond TBO as an unnecessary gamble, while another describes it as a common and accepted practice throughout general aviation. The outcome often turns less on the regulation itself and more on which explanation the jury finds more credible. And while jurors are instructed to decide cases based on the evidence and the law, the reality is that difficult facts and tragic outcomes can influence how maintenance decisions and operational judgments are viewed.
Courts have long recognized that compliance with federal aviation regulations establishes a minimum standard of conduct, but regulatory compliance does not necessarily end the liability analysis. Consequently, an operator can comply with every applicable FAR and still face civil liability if a jury concludes that continuing to operate the aircraft was unreasonable under the circumstances.
Insurance disputes can also follow. Although many policies do not expressly prohibit operation beyond TBO, insurers often examine whether the aircraft was airworthy at the time of the accident and whether maintenance decisions contributed to the loss.
The practical reality is that operating beyond TBO under Part 91 is lawful, common, and often mechanically acceptable. But that does not mean the decision cannot be second-guessed if something happens. After an accident, the central question is not simply whether the regulations permitted the operation. The question becomes whether the operator's decision was reasonable. Thorough documentation, trend monitoring, regular inspections, and a proactive maintenance program can provide powerful evidence that it was.
