Special Flight Permits
For an aircraft that does not currently meet airworthiness requirements because of an overdue inspection, damage, expired replacement times for time-limited parts or other reasons, but is capable of safe flight, a special flight permit may be issued. Special flight permits, often referred to as ferry permits, are issued for the following purposes:
Additional information about special flight permits may be found in 14 CFR part 21. Application forms for special flight permits may be requested from the nearest FAA Flight Standards District Office (FSDO).
The preceding information in this chapter provided general information regarding aircraft inspection. The remainder of this chapter deals with several methods often used on specific components or areas on an aircraft when carrying out the more specific inspections. They are referred to as nondestructive inspection (NDI) or nondestructive testing (NDT). The objective of NDI and NDT is to determine the airworthiness of a component without damaging it, which would render it unairworthy. Some of these methods are simple, requiring little additional expertise, while others are highly sophisticated and require that the technician be highly trained and specially certified.
Additional information on NDI may be found by referring to chapter 5 of FAA Advisory Circular (AC) 43.13-1B, Acceptable Methods, Techniques, and Practices— Aircraft Inspection and Repair. Information regarding training, qualifications, and certification of NDI personnel may be found in FAA Advisory Circular (AC) 65-31A, Training, Qualification and Certification of Non-destructive Inspection (NDI) Personnel.
Before conducting NDI, it is necessary to follow preparatory steps in accordance with procedures specific to that type of inspection. Generally, the parts or areas must be thoroughly cleaned. Some parts must be removed from the aircraft or engine. Others might need to have any paint or protective coating stripped. A complete knowledge of the equipment and procedures is essential and if required, calibration and inspection of the equipment must be current.
Visual inspection can be enhanced by looking at the suspect area with a bright light, a magnifying glass, and a mirror (when required). Some defects might be so obvious that further inspection methods are not required. The lack of visible defects does not necessarily mean further inspection is unnecessary. Some defects may lie beneath the surface or may be so small that the human eye, even with the assistance of a magnifying glass, cannot detect them.
Inspection by use of a borescope is essentially a visual inspection. A borescope is a device that enables the inspector to see inside areas that could not otherwise be inspected without disassembly. An example of an area that can be inspected with a borescope is the inside of a reciprocating engine cylinder. The borescope can be inserted into an open spark plug hole to detect damaged pistons, cylinder walls, or valves. Another example would be the hot section of a turbine engine to which access could be gained through the hole of a removed igniter or removed access plugs specifically installed for inspection purposes.
Borescopes are available in two basic configurations. The simpler of the two is a rigid type of small diameter telescope with a tiny mirror at the end that enables the user to see around corners. The other type uses fiber optics that enables greater flexibility. Many borescopes provide images that can be displayed on a computer or video monitor for better interpretation of what is being viewed and to record images for future reference. Most borescopes also include a light to illuminate the area being viewed.
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