Let’s start being candid. “One of the funny jokes in the aviation industry is a passenger asking if an aircraft is safe enough, and the pilot replying, ‘How do you think it got this old?’” At least once in your lifetime, you might have judged the safety of an airplane by its looks – might have given a thought: How old is this aircraft ? – Is this safe enough to fly with? In this backdrop, this article tries to review the concept of aircraft age and analyse its implications on safety. Also, Nepalese policy arrangement on aircraft import linking with age will be subsequently examined.

Often people look at the chronological age of an aircraft so as to say – when did this aircraft built ? and solely correlate with its airworthiness and safety; the most prioritized area in aviation. However, the age of an aircraft has various facets. Actually, the concept of aircraft ageing is not only limited to chronological age but a combination of it’s chronological age and its operational exposure (e.g. flight cycles or flight hours). To add complexity, it is also affected by various aircraft components that will age at different rates individually. Again, it leads us to one of the most talked about topics in the aviation industry, – Does the chronological age of an aircraft jeopardize safety?  Should states restrict operators from importing aeroplanes based only on age?

First of all, a theoretical aspect of ageing needs to be understood – how ageing over time impacts it’s safety and failure? In terms of reliability engineering which describes a particular hazard function, the aircraft life cycle can be viewed as the bathtub curve (only a simplified form of reality). However, it does not show the failure rate of a single item, but describes the relative failure rate of an entire population of products (aircraft and/or components) over time.

Figure 1: The Bathtub Curve (adapted from weibull.com)

It basically comprises three phases – an infant mortality period with a decreasing failure rate followed by a normal life period (also known as “useful life”) with a low, relatively constant failure rate and concluding with a wear-out period that exhibits an increasing failure rate. From the reliability prospective, an aircraft should be looked into systems, subsystems and even at component level. As an aircraft ages, it passes through aforementioned phases – its useful life into the wear-out phase. The case is similar for its systems, subsystems and components and turns into complexity as these will have non-constant failure rates. Therefore, in aviation business, upgradation and replacement of aircraft components as prescribed by manufacturer and/or regulatory authority is a continuous phenomenon. This cyclic process of upgrading and replacing components continues until it becomes uneconomical to further extend the life of the aircraft (Caruso, 2005). As aircraft age, the time spent on maintenance and the maintenance costs will generally increase. For every 10 years in service, Robinson (2003) suggests that there will be a 15% increase in the time taken to conduct the 100-hourly inspection resulting in an increase in cost. When the cost of maintaining ageing aircraft is considered too high, operators may decide it is more economical to acquire new or newer aircraft. Thus, it comes down to economics – fuel burn, noise,maintenance cost and cost-benefit scenarios.

Keeping all these in mind, practices of states regarding import of aircrafts is an intriguing area in aviation. It is an inevitable argument that aviation safety regulation should  be risk – based and data – driven. However, some states have formulated and implemented age – based  restrictions; varying from 10 to 25 years. For instance, such prescribed limits on imports in passenger aircrafts are 10 years in Indonesia, 15 years in Turkey, 16 years in Thailand, 18 years in India and  20 years in case of Saudi Arabia and South Korea. On the contrary, such restrictions in freighter aircrafts are the same or at maximum ten years more. India amended its Civil Aviation Requirements last year so as to improve ease of doing business as operators with the provision of importing older planes. It specifies lack of knowledge and product support in respect of aircraft (capability to conduct major modifications / inspections in line with programs issued by manufacturers/ regulatory authorities) as a reason behind age based restrictions. Provisions are as follows;

  • Shall not have completed 18 years of age or 65% of designed economic life, whichever is earlier.
  • aircraft above 15 Years of age, the aircraft shall have flown at least for 100 Hours during the last six months from the date of application for import.
  • unpressurised aircraft, the decision will be on a case to case basis and on a complete examination of the record of the aircraft being procured. However, the Director General of Civil Aviation would normally not allow such aircraft which are more than 20 years old.

Similarly, in Egypt, the restrictions reflecting age based restrictions are contained in Egyptian Civil Aviation Regulations, Part 47. The specific limits on age are follows:

  • Passenger aircraft max. take-off weight over 5700 kg should not exceed 17 years from manufacture date.
  • Cargo aircraft max. take-off weight over 5700 kg should not exceed 20 years from manufacture date.

The wide difference in various countries shows that aircraft imports restrictions based on age do not necessarily have a specific technical reasoning. In case of Nepal, Civil Aviation Policy, 2063 BS under the topic Flight Safety stated policy of limiting import of pressurised aeroplanes of over 15 years, 75% of economic design life, 45,000 pressurization cycles. After completion of 13 years of such provision in policy, the draft policy 2077BS has prescribed limits of 12 years of age or 50% of the economic design life or 35,000 pressurization cycles for pressurized aircraft and 15 years of age for non-pressurized aircraft. Aircraft intended to be imported for air cargo operations shall not have completed 25 years in age or 75 percent of its design economic life cycles or 45,000 landing cycles, whichever limitation is completed earlier.


When we look at data related to age of aircrafts in operation globally, the International Air Transport Association (IATA) in 2018 clearly said that about 700 aircraft were retired annually, with an average age of around 27 years. Moreover, it stated that more than 27,000 commercial aircrafts are in service globally; the mean airframe age of which is about 13 years with more than 20% older than 20 years. In a similar study conducted by SGI Aviation, a distribution of aircraft retirement age from 1980 to 2017 and the percentage of retired fleet by ages was analysed. It was determined from the study that the median retirement age for commercial aircraft over the last 36 years is 25 years, with more than half of the aircraft retired between the age of 20 and 30 years. About 10% of aircraft were retired before the age of 17 years and about the same percentage were retired after 35 years of age. The average retirement age of freighter aircraft is 32.5 years and 25.9 years for passenger aircraft; indicating there are major retirement behaviours between freighter and passenger aircrafts. An important study conducted by MIT in 2014 concluded that the historical analysis does not support age-based import restrictions as an effective measure to increase aviation safety. To be specific, this study indicates that there is no correlation between the fatal accident rates and aircraft age up to 27 years of age for commercial jet aircraft with a MTOW greater than 60,000 lbs. When all accidents are considered there is no correlation between accident rates and age up till 18 years and a weak trend of increased accident rate with age is observed for aircraft older than 20 years. This increase in the worldwide accident rate is driven mainly by Africa which exhibits a statistically significant increase in accident rate for aircraft older than 20 years.

From the literature, it can be concluded that if chronological age is not a valid indicator of increased safety risk, then imposing conservative age based import restrictions reduce the population of available air transport aircraft and thereby increase the cost and reduce the access to air transportation for those states that impose such restrictions. To be precise, we should carefully examine and interpret the safety related data/information including accidents and serious incidents with the ageing of aircraft. Thus, it becomes necessary to conduct data driven studies on this matter. The governing barometer should also take into account the original operator, the aircraft’s maintenance history and the maintenance capability for importing aircrafts. Moreover, a sufficiently resourced maintenance program and the continuous support of the manufacturers should be ensured. Managing the consequences of an ageing aircraft requires cooperative approaches by operators, manufacturers and national regulators to ensure that any defects identified by one operator are notified quickly and efficiently within the industry. Lack of such approaches by stakeholders concerned might have been a factor behind imposing limits in various countries including Nepal.

To sum up, it has been observed from various documents that the states utilize their statutary laws to limit the aircraft import based on its age. The non-uniformity in such decisions/requirements precisely shows that there is a lack of safety related data analysis. Such restrictions might diminish an enabling business environment for current investors and prospect investors in the aviation industry. Investing a huge chunk in aviation infrastructure doesn’t have a meaning without the growth of airlines and other service providers. Hence,  Nepal which is willing to improve its connectivity, promote tourism, travel and trade via aviation must handle this sort of policy decisions carefully. The proposed limits of 12 years on aircraft import that is one of the most stringent impositions in this region must be re-evaluated before implementation. The policy might  pose  hurdles for operators in fleet acquisition either through purchase or leasing at a time when Nepal is pushing for increased regional and global air connectivity. The regulatory capability, available resources, international practices, prevailing situation of aviation, utilization of upcoming infrastructures and the aspirational goal of the nation in the aviation sector should be considered tactfully. Safety data should be examined against the age of the aircrafts. This would be one fascinating area of research for aviation enthusiasts in days to come.


By : Mr. Mukesh Dangol