(2) Functional description - A reasonable altitude is verified in one of two ways.
 -for the ILS approaches, the glide slope deviation is used to verify a "normal" approach,
 -when the ILS information is not available, terrain and altitude
 matching is used to verify a "normal" approach. 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
 -localizer deviation from the ILS
 -aircraft magnetic track angle from the FMGC or the ADIRU
 -runway course from the ILS
 -corrected barometric altitude from the ADIRU
 -QNH or QFE mode of baro altitude correction via program pin. QNH mode is 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 airports. 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
R basic latitude and longitude data. If the FMGC data are invalid, or R missing, then the GPWC will automatically switch back to the ADIRU data.
 (3) Types of envelope modulation - There are currently four types of envelope modulation required for the airport approaches causing problems for the GPWC.
 -bias the mode 1 warning boundaries for SINK RATE and PULL UP to the right to allow greater altitude descent rate before a warning is generated. (Ref. Fig. 007)
 -
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. 008)

 -
lower the maximum upper limit for mode 4 to allow less minimum terrain clearance before a warning is generated. (Ref. Fig. 010)

 -expand the maximum mode 5 radio altitude level where a warning can begin. This will allow GLIDE SLOPE warnings for higher radio
R 1EFF : 001-004, 051-060, 1 34-48-00Page 32 1 1 Config-2 May 01/05 1 1 1CES 1 altitudes. The gear down requirement is also removed during warning expansion, to allow gear up warnings.

 (4) List of envelope modulation airports The following list represents the status of airports with Envelope Modulations. The majority of the identified areas require Mode 2A envelope modulations.
 (a)
 EUROPE ALICANTE SPAIN ILS RWY 11 GENEVA SWITZERLAND ILS RWY 05 NURNBERG GERMANY R.V. TO ILS OR NDB RWY 28 TENERIFE CANARY IS. ILS RWY 30

 (b)
 NORTH AMERICA
 NORTH BAY ONTARIO I.A. TO VOR DME YYB
 ONTARIO CA VOR RWY 26R
 RENO NV LOC DME B/C-B
 SAN DIEGO CA LOC DME B/C RWY 27

 (c)
 SOUTH AMERICA
 CUENCA EQUADOR ILS/DME RWY 23
 QUITO EQUADOR DEP RWY 17/ILS RWY 35

 (d)
 FAR EAST
 HONG KONG (A) B.C.C. IGS/NDB RWY 13
 KAGOSHIMA JAPAN ILS RWY 34
 SEOUL S. KOREA I.A. VOR DME RWY 32

 (e)
 PACIFIC
 AGANA NAS (A) GUAM IS. ILS RWY 6L
 AGANA NAS (B+C) GUAM IS. ILS RWY 6L
 HIROSHIMA JAPAN I.A. NDB LOC RWY 4
 TAIPEI TAIWAN ILS-1 RWY 10

R **ON A/C 001-049, 051-060, 101-104,
R Post SB 34-1147 For A/C 001-004,051-060,
 C. Envelope Modulation
 (1) Background During the past 20 years, experience with GPWS have shown that normal approaches to certain airports can be incompatible with the normal warning envelopes and signal filtering. A number of enhancements to the envelopes and filters have been developed during this time in an attempt to accommodate these few
R 1EFF : 001-049, 051-060, 101-104, 1 34-48-00Page 33 1 1 Config-2 May 01/05 1 1 1CES 1 airports, without compromising the overall GPWS effectiveness for all the other "normal" airport approaches. However, there remain a limited number of cases which are still not satisfactory despite these efforts. All of the noticeable cases have been due to nuisance warnings for approaches and departures at particular airports. The majority of nuisance warnings involves Mode 2 closure rate due to terrain under the approach path or rising terrain just before the runway threshold. Others involve Mode 4 terrain clearance warnings during initial approach. A few Mode 1 warnings are the results of steeper than 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 when the upper limit of Mode 5 is 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 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 that the aircraft is at a reasonable altitude before desensitizing any warning criteria. If the aircraft is already low, further warning reduction is not desirable.
　
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