When most of us think of an aircraft we think of the outside of the plane that has the wings, the windshield, the engines, and propellers.  On the inside of a plane most of us think of the cockpit and the main cabin, but all of these places are made up of many different parts. 

There are many parts and pieces that create an aircraft and when you own or fly a plane you know that some of these pieces need to be replaced from time to time.  Like any sort of moving object, pieces wear out or simply don't operate or look cosmetically as good as they once did.  When parts wear out and need to be replaced the whole aircraft isn't obsolete, instead parts must be purchased and then installed on the plane. 

As you might have assumed, there are many different parts of an aircraft that may or may not need to be replaced during the lifetime of the plane.  When most of us think of an airplane part we think of the seats, the seatbelts, the carpet, overhead bins, and the little fold out tables. 

While these are just cosmetic additions to an aircraft they are some of the pieces of the plane that wear out quite quickly and need to be replaced.  Most commercial airlines have thousands of replacement pieces for each of these things and they can just swap them out as needed.   

Then there are the exterior parts of an aircraft that many of us think of such as the propellers, engines, wings, windshield, and tires.  These are the parts of the aircraft that deal with the elements, and because of this they are often repaired and replaced as needed.  All planes, especially commercial variants, are inspected to ensure that they meet minimum safety requirements. 

During these inspections many things may be found to be in disrepair and they then are grounded until the faulty or worn out aircraft parts can be replaced or repaired. 

There are a lot of parts of an aircraft that will become faulty or simply become outdated that will need to be replaced during the life of the aircraft.  Some of these things include audio panels, autopilots, HF radios, radar altimeters, storm scopes, transponders, weather radars, and more. 

Many pieces of the actual aircraft frame will need to be replaced, as well.  Just like your car or any other moving piece of equipment, there are a lot of little parts and pieces that wear out and need to be maintained. 

When an aircraft part needs to be replaced, an aircraft owner or commercial airline needs a parts dealer.  Most commercial airlines keep stock of the typical parts that need to be replaced or repaired, but they get these parts from the parts dealer. These parts dealers have pieces ranging from very small to very large, and depending on the dealer that you go to, you may find that they specialize in one or two aspects of aircraft parts instead of having any part for any aircraft. 

Generally you will find that aircraft parts dealers will specialize in one type of aircraft, allowing you to easily find the dealer and the parts that you need.