21 days prior to the effective date of the revision.  The integrity of the data is ensured through a process called  cyclic redundancy check (CRC). A CRC is an error detection  algorithm capable of detecting small bit-level changes in  a block of data. The CRC algorithm treats a data block as  a single, large binary value. The data block is divided by a  fixed binary number called a generator polynomial whose  form and magnitude is determined based on the level of  integrity desired. The remainder of the division is the CRC  value for the data block. This value is stored and transmitted  with the corresponding data block. The integrity of the  data is checked by reapplying the CRC algorithm prior to  distribution.  the pilot to make an immediate turn toward the Durango  VOR instead of flying the series of headings that terminate  at specific altitudes as dictated by the approach procedure.  [Figure 6-28] Pilots must be aware of their individual  systems Path and Terminator handling characteristics  and always review the manufacturer’s documentation to  familiarize themselves with the capabilities of the RNAV  equipment they are operating. Pilots should be aware that  some RNAV equipment was designed without the fly-over  capability which can cause problems for pilots attempting  to use this equipment to fly complex flightpaths in the  departure, arrival, or approach environments.  When avionics manufacturers develop a piece of  equipment that requires an airborne navigation database,  they typically form an agreement with a database provider  to supply the database for that new avionics platform. It  is up to the manufacturer to determine what information  to include in the database for their system. In some cases,  the navigation data provider has to significantly reduce the  number of records in the database to accommodate the  storage capacity of the manufacturer’s new product, which  means that the database may not contain all procedures.  Compiling and maintaining a worldwide airborne  navigation database is a large and complex job. Within the  United States, the FAA sources give the database providers  information, in many different formats, which must be  analyzed, edited, and processed before it can be coded  into the database. In some cases, data from outside the  United States must be translated into English so it may be  analyzed and entered into the database. Once the data is  coded, it must be continually updated and maintained.  Once the FAA notifies the database provider that a change  is necessary, the update process begins. The change is  incorporated into a 28-day airborne database revision cycle  based on its assigned priority. If the information does not  reach the coding phase prior to its cutoff date (the date that  new aeronautical information can no longer be included  in the next update), it is held out of revision until the next  cycle. The cutoff date for aeronautical databases is typically  Another important fact to remember is that although there  are standard naming conventions included in the ARINC  424 specification, each manufacturer determines how  the names of fixes and procedures are displayed to the  pilot. This means that although the database may specify  Role of the Avionics Manufacturer  Role of the Database Provider  Figure 6-29. Naming conventions of three different systems for the VOR 34 Approach.  6-13  EUGA <VOR 34  >APR  IAF / TRAN: D130N I F 