What is Tslovh in Aviation? (Time Since Last Overhaul)

Time since last overhaul (TSLOVH) is a vital term in aviation maintenance. It refers to the time elapsed since the last overhaul of an aircraft or its systems. Overhaul refers to a comprehensive maintenance process that involves the disassembly, inspection, repair, replacement, and testing of various components of an aircraft.

TSLOVH is an essential measure that ensures aircraft safety, reliability, and cost-effectiveness. Airlines and aviation authorities set specific requirements regarding the interval between overhauls of various aircraft parts. They typically refer to a specific number of flight hours, calendar time, or cycles.

In this article, we will discuss the various aspects of TSLOVH and why it is crucial in aviation maintenance.

Factors Affecting TSLOVH

Several factors influence the TSLOVH of an aircraft or its components. Knowing these factors can help airlines and maintenance crews plan the maintenance schedule efficiently.

Flight Hours

Flight hours refer to the amount of time an aircraft spends in the air during a flight. The more a plane flies, the faster its components wear out, requiring more frequent overhauls. Therefore, airlines usually set a maximum flight hours limit for aircraft parts before they need an overhaul.

For example, the engines of a Boeing 747 typically have a maximum time-in-service of around 25,000 hours before they need an overhaul. This number may vary depending on the aircraft model and engine type.

Calendar Time

Calendar time refers to the time elapsed since the aircraft or its components underwent an overhaul. Even if an aircraft is not flying, its components can also age and degrade over time due to environmental factors such as temperature, humidity, and atmospheric pressure.

Therefore, airlines and regulatory authorities typically require overhauls after a certain number of years, regardless of flight hours. For example, the Federal Aviation Administration (FAA) requires overhauls of certain aircraft parts every 3,600 calendar days, regardless of usage.


Aircraft cycles refer to the number of takeoffs and landings an aircraft performs. Takeoffs and landings exert significant stress and wear on aircraft components, especially the landing gear and brakes. Therefore, these parts typically have a maximum number of cycles before they need an overhaul.

For example, the landing gears of a Boeing 747 typically have a maximum number of cycles of around 20,000 before they need an overhaul.

The Importance of Timely Overhauls

Timely overhauls ensure that aircraft remain safe, reliable, and cost-effective to operate. Neglecting overhauls can result in catastrophic failures, leading to accidents and fatalities. Furthermore, early overhaul detection can prevent extensive and expensive repairs, reducing aircraft downtime and maintenance costs.

Enhanced Safety

Regular overhauls of aircraft parts ensure that they are in good working condition and free of defects that could compromise safety. Overhaul inspections involve disassembling and inspecting all components of an aircraft part, treating any defect found, and replacing worn-out parts.

For example, an airplanes’ engines are the most critical components requiring regular overhauls. Failure of one or both engines can be catastrophic; thus, airlines adhere to strict engine overhaul schedules. Overhauls determine the cause of engine problems and identify cost-effective solutions for mitigating risk.

Reduced Downtime

Early detection of potential problems during overhauls prevents unexpected breakdowns that require time-consuming and expensive repairs. Furthermore, regular overhauls ensure that aircraft components operate at peak performance, reducing maintenance downtime.

Taking engines as an example, overhauls increase the lifespan of the engine, reducing the need for complete replacement, avoiding costly downtime.

Cost-Effective Operations

Regular overhauls help airlines operate their fleets more cost-effectively. Complete overhauls are generally cheaper than repairs needed as a result of delayed maintenance.

For instance, overhauling an engine may cost $200,000, while repairing it due to delayed maintenance can cost upwards of $2 million. If an engine failure results in a flight delay or cancellation, passengers may seek compensation, which can add up to significant losses.

The TSLOVH Process

TSLOVH is an essential process that ensures aircraft safety, longevity, and cost-effectiveness. The following steps outline the TSLOVH process:

Task Identification

The first step of the TSLOVH process is to identify the aircraft components and systems that require overhauls, based on their history, type, and usage. Depending on the aircraft and its systems, time, or cycle-based inspection intervals exist.

The planning phase is crucial, as any missed overhaul requirements can lead to more challenging and complex problems, resulting in increased costs and aircraft downtime.

Disassembly and Inspection

Disassembly and inspection are the most critical steps in the TSLOVH process. Overhaul specialists disassemble the aircraft components, inspect each part, and determine the degree of wear and tear, defects, cracks, and other faults. Worn-out parts are replaced, and faulty components are repaired.

The process requires specialized equipment, professional knowledge, and expertise. It typically takes several weeks, depending on the complexity of the component and the amount of work required.

Reassembly and Testing

After replacing and repairing worn-out parts, overhaul specialists reassemble the aircraft components and perform thorough tests before returning them to service. Testing ensures that the overhauled components meet safety and performance standards and function correctly while minimizing downtime.

The Bottom Line

Time since the last overhaul is a crucial term in aviation, referring to the duration between overhauls of an aircraft or its components. Regular overhauls ensure aircraft safety, reliability, and cost-effectiveness, reducing maintenance costs and avoiding catastrophic failures.

Airlines must have scheduled maintenance plans that adhere to specific regulatory requirements. Overhaul specialists must have specialized equipment, expertise, and knowledge to identify, disassemble, inspect, repair, and reassemble aircraft parts and systems efficiently.

Regular overhauls are a critical component of aircraft maintenance and safety. Neglecting maintenance leads to expensive and time-consuming repairs, costly downtime, and even catastrophic failures that can lead to injuries or fatalities.

For more aviation terminology, please visit Federal Aviation Administration (FAA)