Aging Is Not For The Faint-Hearted

Applies to people and pilots
Bill De Decker
May 29, 2007
By Bill De Decker
Aging is not for the faint-hearted. This applies to people and it applies to aircraft. As aircraft age, repairs become more frequent and parts for these older aircraft become harder to find. The problems multiply and the cost of maintenance increases rapidly. Our research shows that a 25- to 30-year-old aircraft costs almost twice as much to maintain as a five-year-old one. However, that is not the only place where old aircraft impose a substantial cost burden. The other thing that happens is that as the required maintenance effort increases, so does the time required to accomplish the maintenance. As a result, availability starts to decrease and in turn the revenue potential decreases. Ultimately reliability also starts to decrease and finally, when a particular aircraft is causing too many problems, the decision is made to withdraw it from service and use it for parts.

Everyone knows that this happens, but there is not much written about the details or the impact of the aircraft aging process on availability, reliability or how long aircraft stay in service. So, over the course of the last five years, we have done some really interesting research and thought we would it share with you.

The first question we had was: How long do aircraft actually stay in service? By combining data from several sources on the service status of individual serial numbers and their year of manufacture, we were able to determine, by make/model and year what percent of aircraft manufactured in a particular year have been withdrawn from service. The accompanying graph plots the answers. It shows that for some 5,500 turbine-powered fixed- and rotary-wing aircraft, 10% of the 25-year-old, 20% of the 30-yearold and 50% of the 35-year-old aircraft have been retired from service. That's the average. However, there are large variations between particular makes/ models and the average.

Makes and models that have strong support programs and are considered to be ‘money makers’ tend to stay in service longer, particularly if there is no modern-day equivalent. On the other hand, aircraft that have poor support programs, are ‘orphans’ (the original equipment manufacturer no longer is in the aircraft business) or are not considered cost-effective tend to get withdrawn from service much sooner.

The next question then is: Why do aircraft get withdrawn from service? Analysis and discussions with operators indicate there are four factors:

• Poor reliability

• Low availability

• High cost of labour

• High cost of parts

Reliability is usually measured as a percentage of the number of departures that occur within a specified number of minutes from the scheduled departure time and is expressed as ‘dispatch reliability’. It is calculated by dividing the number of departures in a month or a year that are delayed by more than a certain amount of time by the total number of departures for that aircraft during that period. Thus if on average one departure in 50 is delayed, the dispatch reliability is calculated as 98%. Airlines aim for and get a 98 to 99% mechanical dispatch reliability rate. Limited data indicates that commercial operators of turbine aircraft get the same sort of mechanical reliability. However, as the aircraft ages, it takes more and more maintenance to achieve any kind of acceptable on-time departure rate.

In other words, keeping aircraft reliable as they age means more and more time spent in the hangar and less and less time available for flight operations. The accompanying graph shows what happens to availability as aircraft age. This data covers some 200 fixed- and rotary-wing aircraft operated by various government agencies and shows clearly that as aircraft get older, it becomes more and more difficult to maintain a high degree of availability. Each data point shows the availability for one aircraft or fleet of similar aircraft at their actual or average age.

The data show that even under the best of circumstances avail- ability starts to decrease when the aircraft is 20 to 25 years old. On average, at 30 to 35 years of age, availability is down to 50% – i.e., you need two aircraft to have one available at any one time.

The impact of this decrease in availability on the revenue-generating ability of the aircraft is shown in an accompanying table. This shows that for a typical operator flying an average of two hours per day, the loss of revenue ($72,000 per year) is minimal with an aircraft less than 15 to 20 years old. Once the helicopter passes 20 years in age, the availability starts to decrease rapidly and the lost revenue starts to increase. Thus, when the aircraft is 30 to 35 years old, the lost revenue equals $364,000 for this example and it probably becomes very difficult to make money with such a helicopter.

As with any theoretical analysis, there are exceptions and the helicopter business is no different. There are operators that successfully operate old equipment (such as 30/40-year-old Sikorsky S-58Ts, Hueys, Bell 205s and S- 61s). They specialize in operating these machines because there are no good modern replacements available. They also know that it takes two or three helicopters of that vintage to serve a contract that stipulates the availability of one aircraft and have geared their operation to deal with this. And if their cost structure is set up right, they can make good money.

For other operators, it may well be worth keeping the cost of increased maintenance and the lost revenue of decreased availability in mind as they contemplate their fleet and its ability to make a good profit.

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