This can be a big question, but it doesn't need to be with a qualified professional at your side.

Sometimes it is clear, perhaps the owner just wants bigger, better or faster? However, the most difficult decisions normally concern an aircraft that is over 20 years old and still useful.

Deciding when to replace your aircraft is a complex decision, make sure you gather (all) the data to take emotion out of the equation!

The tops 3 reasons to retire your aircraft are usually:

1. Obsolescence - it lacks the required technology or parts are nolonger available.
2. Reliability - or rather lack of it, and the aircraft can't be trusted for any given schedule or flight.
3. Cost - maintenance is more expensive because there are more inspections, more component failures, parts are more expensive and troubleshooting is more frequent. There is a higher fuel burn and technology limits possible savings otherwise.

If you are serious about replacing your aircraft, the following link refers an excellent article which should be consulted. 

NOTE: Subcripstion for at least 1 year will be required to access the article.

http://aviationweek.com/awin/when-say-goodbye-your-airplane

Qjet understands what it means to take a good decision and would be honored to help you make well informed and good decisions! Please call us if you need help.