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The biggest issue with aging aircraft is that the repair and replacement of parts increase the cost of owning and operating the aircraft. This hurts in two ways. One is the increased costs, which are obvious.
A 20-year old aircraft has about 50 - 60% higher maintenance costs than a new aircraft just out of warranty - excluding the engines! The early years when the aircraft are young and warranties are in effect show very low maintenance costs - less than half of what they are at year 5. However, when the aircraft is 30 years old and wear and tear is taking its toll, the maintenance costs are typically more than double what they were at year 5. As with any mechanical device, this makes sense. The increased maintenance (parts and labor) is primarily due to unscheduled maintenance. Much of the unscheduled maintenance occurs as part of the scheduled inspections - i.e. during the scheduled maintenance check an item is found out of tolerance and is repaired, replaced or overhauled.
The biggest thing you can do is to keep the aircraft well maintained from day one! Don't put off maintenance; keep the aircraft in top condition. When evaluating used aircraft, if the maintenance records are not in excellent condition - how do you know the maintenance was done properly? That low price for the used aircraft may more than make up the difference with some unplanned-for maintenance costs.
Increased maintenance leads to the second big problem: decreased availability.
Availability is defined as the number of days an aircraft is available for flight operations divided by the total number of days in the operating year. In other words, if the aircraft is in the shop, it isn't available for flight.
Our data suggests this becomes a serious issue for aircraft older than about 20 years of age. Availability drops from a high of 95% for newer aircraft, to an average of 70% at age 25, dropping to no better than 55% at age 30. Looking at it another way, it typically takes two older aircraft to have the same availability as one newer one!
Another issue that can make this worse - limited spare parts availability. There are many cases where due to the limited number of aircraft flying, parts suppliers maintain a very minimal inventory and don't replenish the stock until after they run out. Even with larger fleet numbers, certain components may be manufactured in limited quantities by manufacturers who infrequently open up the production line to make more spares.
If you don't fly a lot of hours and can schedule trips well in advance, then you may be able to deal with reduced availability. Still, we've had customers who fly three aircraft - one on the schedule, one back-up and one in the shop. That gets costly!
The last issue isn't one just yet. The General Aviation Revitalization Act of 1994 released the OEMs from much of the liability for the design and safety features of older aircraft. There have been a few reports of maintenance shops not wanting to work on aircraft older than 18 years of age out of concern for the liability potentially falling on the maintenance shop should an accident occur.
Given the number of aircraft built prior to 1994, I doubt this will force many maintenance providers to turn away large numbers of aircraft - but I would not be surprised to see an increase in isolated cases of refusals or release forms being presented to owners before their aircraft is worked on. Before signing any releases, check with your own aircraft insurance carrier to make sure they will cover you.
Older aircraft can be productive for many years. They do require more maintenance and at some point their cost and declining availability make them less useful to many. When to replace an aircraft is not an easy formula. It does require monitoring and tracking of costs and availability, and a willingness to say goodbye to an old friend.
As always we look forward to your comments and opinions.