normal approaches over terrain which slopes down to the runway at some airports. A different type of case is the inadequate warning protection during ILS approaches because Mode 5 is limited to less than 1000 ft. radio altitude. There are airports located at a significantly higher altitude than the surrounding terrain. In some instances this difference is over 1000 ft., thus requiring the aircraft to be below the runway elevation before a Mode 5 warning is possible during most of the approach. Until recently there has been no reasonable way to accomodate these few special cases without compromising the Enhanced GPWC at all other airports. What is needed is the ability to recognize when the aircraft is approaching one of these airports and then adjust the warning criteria to suit the particular approach. The availability of accurate, low drift, latitude and longitude information from the latest generation inertial navigation equipment now makes individual airport recognition possible. After recognizing the approach to or departure from one of these airports, it is also important to verify the aircraft is at a reasonable altitude before desensitizing any warning criteria. If the aircraft is already low, further warning reduction is not desirable. This requires the use of corrected altitude signals.
 (2) Functional description Furthermore, in order to prevent inadvertent activation of envelope modulation, cross checks must be made which validate the navigational and altitude information. This requires a cross check to other ground based navigational aids. Corrected altitude information from the ADIRU is used. This data can be either QNH or QFE corrected (selectable via program pin). This altitude information is verified in one of two ways:
 -For ILS approaches, the glide slope deviation is used to establish that adequate terrain clearance exists (i.e. a "normal" approach). Consequently, errors in altitude data do not enable envelope modulation during an unsafe condition,
 -When ILS information is not available, stored terrain elevation data is matched against computed elevation data (i.e. corrected altitude - radio altitude) to verify altitude. This is done for a "snapshot" location immediately prior to the envelope modulation area.
 The following input data are used for airport recognition:
 -latitude position from the FMGC or the ADIRU,
 -longitude position from the FMGC or the ADIRU,
 -glide slope deviation from the ILS portion of the MMR,
 -localizer deviation from the ILS portion of the MMR,
 -aircraft magnetic track angle from the FMGC or the ADIRU,
 1EFF : ALL 1 34-48-00Page A1 1 1 Config-1 Aug 01/05R 1 1 1CES 1

 -runway course from the ILS portion of the MMR,
 -corrected barometric altitude from the ADIRU,
 -QNH or QFE mode of baro altitude correction via program pin. QNH mode is the baro altitude correction to sea level. QFE mode is selected with a program pin for baro altitude correction to the airport field elevation,
 -radio altitude. Latitude and longitude data are continuously monitored for the airport locations. Additional data processing for envelope modulation is not required until the aircraft approaches one of the envelope modulation areas. Then the other data inputs are checked for a "normal" approach before any warning envelopes are modulated. The FMGC is the preferred source for latitude and longitude data because these data were corrected for the normal drift of the ADIRU basic latitude and longitude data.
 (3) Types of envelope modulation - There are currently four types of envelope modulation required for particular airport approaches.
 -bias the Mode 1 warning boundaries for SINK RATE and PULL UP to the right to allow greater altitude descent rates before a warning is generated. (Ref. Fig. 010)
 -
lower the maximum upper limit for Mode 2A and Mode 2B. This limits the maximum radio altitude, or the minimum terrain clearance required to generate a warning. (Ref. Fig. 011)

 -
lower the maximum upper limit for Mode 4 to allow less minimum terrain clearance before a warning is generated.

R **ON A/C 106-149, 220-299, 301-399, 401-499,
 (Ref. Fig. 014)
 **ON A/C 001-049, 051-099, 101-105, 151-199, 201-219,
 Post SB 34-1147 For A/C 001-004,051-060,
 (Ref. Fig. 014A)
 **ON A/C ALL
 Post SB 34-1147 For A/C 001-004,051-060,
 -expand the maximum Mode 5 radio altitude level where a warning can begin. This allows GLIDE SLOPE warnings for higher radio altitudes.
 1EFF : ALL 1 34-48-00Page A2 1 1 Config-1 Aug 01/05 1 1 1CES 1 The gear down requirement is also removed during warning expansion,

 to allow gear up warnings. The actual data for each of the established areas is in tables stored in the Enhanced GPWC non-volatile memory. This data can be for either a "snapshot" area or an envelope modulation area. In fact, these areas can actually overlap since the envelope modulation is not performed until the "snapshot" conditions have been verified. Every "snapshot" has an associated envelope modulation area, but not every envelope modulation area has an associated "snapshot" area. This is because some locations use glide slope instead of the "snapshot" feature as a cross check on corrected altitude data. All of the data extracted for each location is used to form a unique key which establishes the aircraft position, orientation and altitude. Stored data for latitude, longitude, terrain elevation, expected elevation tolerance, minimum expected radio altitude, heading (track) and maximum allowable time to reach the envelope modulation area are compared to real time computed values for these parameters in order to set "snapshot" latch. This latch is intentionally stored in volatile RAM memory and cleared during power loss recovery. The associated signal validities are used to establish signal integrity prior to setting the "snapshot" latch. The maximum time term is used to clear the "snapshot" latch once this time has expired unless the envelope modulation conditions are satisfied first. Logic is required to satisfy one or more of the envelope modulation "keys". In each case, if the "key" is required, the associated conditions are monitored. The following is a summary of the envelope modulation, and snapshot keys:
　
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