DER-repairs are individual repair techniques that return a damaged part or component to its original design specifications. All alternative repair procedures must be authorized by a Civil Aviation Authority Designated Engineering Representative (DER). The DER will determine which procedure is appropriate based on their assessment of the damage.
The most common types of repairs include: welds, rivets, and screws. Less common methods include using adhesive or heat-shrink tubing to repair mechanical components. Most repairs require some type of metal working equipment such as a drill or milling machine. In some cases, specialized tools may be required for difficult-to-reach areas.
In general, every aircraft component can fail at any time due to manufacturing defects or abuse by passengers and crew. Even if an item appears to function normally, it may still be defective and should be replaced before further use. Aircraft components are usually designed to be repaired instead of replaced because this process is less expensive over the long term.
It is important to understand that each repair changes the structural integrity of the item being fixed. Therefore, care must be taken not to apply excessive loadings in order to avoid causing more serious damage to other parts of the aircraft. Repair manuals often specify maximum loads that certain components can withstand without failure.
When a system or component is derated, it is operated below its typical working limit. This lessens the component's degradation rate and the number of failures caused by harsh operating circumstances. Component manufacturers often rate systems to indicate what kind of operating conditions they can withstand without failure. A manufacturer may also rate components that do not come with their own display instrument cluster because they know that many drivers will use their cars in ways that would cause them to malfunction soon anyway. For example, a driver might leave a key in the ignition while his car is in storage if he knows he will be using it shortly.
Components that are derated will still operate properly in normal use cases but will fail sooner than expected under tough conditions. Derating is usually done to avoid damaging the item beyond repair or causing other problems by using it at speeds or for long periods that it was not designed for. For example, an engine might be derated when running on a track day to prevent damage to the engine from overheating. Derating is also necessary for items like batteries that cannot be rebuilt. Batteries must be replaced after several charges due to chemical changes that take place as they are used over time.
Things that are derated include engines, batteries, and transmission fluids. As these items wear down over time they become less efficient at performing their functions.
Derating is a deliberate technique that is done to each component of a product to limit the possibility of a component experiencing greater stress than it is capable of withstanding. The increased toughness also minimizes the amount of damage that stress may cause, extending the component's life. Derating can be performed during design or production, but it is most often done during development to avoid wasting material.
There are two types of derating: intrinsic and extrinsic. Intrinsic derating is required to ensure that components do not fail prematurely due to excessive stresses caused by manufacturing errors or customer misuse. Extrinsic derating is required to ensure that components perform within their specifications even under conditions that will likely cause them to fail prematurely in less experienced users' hands (e.g., powering aircraft engines at temperatures below 0 degrees Celsius).
Intrinsic derating should be done based on analysis of the component's load-displacement curve. This curve shows how much force is needed to deform a component proportionally as function of its thickness. For example, if a bolt is too thin, it will break before it has been stretched enough to transmit its maximum possible strength. A thicker bolt would be required to prevent this from happening. Thickness is only one factor among many others that affect the behavior of bolts, but it is sufficient to explain why thick bolts are necessary for strong connections.
Derating (or de-rating) in electronics is the operating of a device at a lower capacity than its rated maximum capability in order to extend its life. Operation below the maximum power rating, current rating, or voltage rating are common instances. Derating is usually required for safety reasons during installation and use of equipment.
The term comes from the need to limit the maximum speed of electrical machinery so as not to damage the components. If the machine is designed to run at full speed indefinitely, it will eventually burn out. By limiting the speed, the lifetime can be extended greatly without changing the design specifications.
For example, if a motor is specified to run at 200 rpm, then it should not be driven at its maximum possible speed of 4000 rpm. It would likely fail early due to excessive stress on its bearings or other components.
There are two types of derating: mechanical and electronic. Electronic derating can be done by using a resistor or capacitor. The goal is to reduce the load on the component so that it will last longer. For example, if a motor is expected to pull 100 lb with no problem, putting a 10K resistor in series with it will cut its load down to 10 lb, which is still enough to move something but not enough to cause it to break down prematurely.
Interchangeable parts, or identical components that may be swapped out for one another, have a long history in manufacturing. The expression "interchangeable part" was first used by Henry Ford in an article published in 1922. He called these components "individual units which could be replaced by other individually made units if they failed to meet standards set by management."
Ford's use of the term interchangeably comes from the fact that they are all the same type of component: bolts, bearings, and screws. Today, these items are made in large quantities, usually with machine tools, and so they can be considered interchangeable.
The concept of interchangeable parts has many implications for efficiency in production and quality control. By using this method, companies can avoid making multiple versions of the same product, which would increase costs. They also can modify existing products without having to make large changes, which would be difficult or impossible with some other manufacturing processes.
Interchangeable parts also help companies save money because they can be reused instead of being thrown away after use. This reduces the cost of inventory and waste disposal.
Finally, interchangeable parts allow companies to fix problems on the fly rather than stopping production as done with some other methods.