Enhanced GPWS - Unsafe Terrain Clearance - Mode
Figure 014 (SHEET 2)
R 1EFF : 106-149, 220-299, 301-399, 401-499, 1 34-48-00Page 95 1 1 Config-1 Aug 01/05 1 1 1CES 1
Enhanced GPWS - Unsafe Terrain Clearance - Mode
Figure 014A (SHEET 1)
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 34-48-00Page 96 1201-219, 1Config-1 May 01/05 1 1 1CES 1
Enhanced GPWS - Unsafe Terrain Clearance - Mode
Figure 014A (SHEET 2)
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 34-48-00Page 97 1201-219, 1Config-1 May 01/05 1 1 1CES 1 (f) The gear-down logic requirement for Mode 5is deleted at certains
airports. R
(5) Mode 5 - Descent below glide slope
(Ref. Fig. 015)
(a)
Mode 5 provides two levels of warning when the aircraft flight path descends below the glide slope beam on front course ILS approaches. The upper limit of 1000 ft. nominal allows the capture of the beam before enabling this mode. Higher upper limits are used at certain airports to increase the warning envelope. The deviation boundaries are shown in dots below the beam where one dot equals 0.0875 DDM = 0,36 degree. The first warning occurs whenever the aircraft is more than 1.3 dots below the beam. It is called a soft glide slope warning because the volume level of the GLIDE SLOPE warning is approximately one half (- 6 db) that of the other warnings. A second warning boundary occurs below 300 ft. radio altitude and more than 2 dots below the beam. It is called loud glide slope because the volume level is increased to that of the other warnings.
(b)
Both boundaries allow additional deviation below 150 ft. of radio altitude to allow for normal beam variations near the threshold.
(c)
The basic audio de-clutter feature provides GLIDE SLOPE message logic which suppresses the aural alert after one message has been given. Follow-on alerts are only allowed when the aircraft descends lower on the glide slope beam by approximately 20 per cent. The alert lamp remains on until the excessive FLY UP condition has been corrected. The aural alerts are provided continuously once the aircraft exceeds 2 dots FLY UP. Below 300 ft. AGL the messages speed up as altitude is lowered or deviation is increased. Actual time between GLIDE SLOPE messages for these conditions is controlled by the equation:
RADIO ALTITUDE (FT.) PAUSE(SEC) = ---------------------------------X 0.0067 GLIDE SLOPE DEVIATION (DOTS FLY UP)
Additionally, the audio de-clutter feature allows for Mode 5 GLIDE SLOPE alerts to occur during penetration of the Mode 1 outer envelope while the Mode 1 SINKRATE audio is suppressed.
1EFF : ALL 1 34-48-00Page 98 1 1 Config-1 Aug 01/05 1 1 1CES 1
Enhanced GPWS - Descent Below Glide Slope
Figure 015
R 1EFF : ALL 1 34-48-00Page 99 1 1 Config-1 Aug 01/05 1 1 1CES 1
(d)
The GLIDE SLOPE warning can be manually cancelled by the crew. This can be done any time below 2000 ft. nominal radio altitude. Cancel can be reset by ascending above 2000 ft. nominal, or descending below 30 ft.
(e)
The change from constant deviation to a slope below 150 ft. radio altitude is shown along with the constant separation 0.7 dot between the two boundaries. A delay of approximately 0.8 second is inserted between the warning output and the enabling logic during a warning condition. The delay also turns off the warning output when two successive samples show a loss of the enabling logic. The repetition rate of the GLIDE SLOPE message is controlled by the radio altitude and the glide slope deviation as shown in the equation above.
(f)
The gear-down logic requirement for Mode 5 is deleted at certain airports.
**ON A/C ALL
Post SB 34-1147 For A/C 001-004,051-060,
C. Envelope Modulation
(1) Background During the past 20 years, experience with GPWS has shown that normal approaches to certain airports can be incompatible with the normal warning envelopes and signal filtering. The envelope modulation feature provides improved alert/warning protection at some key locations throughout the world, while improving nuisance margins at others. This is made possible with the use of navigational signals from modern inertially based navigation equipment. This feature utilizes updated flight management system navigational signals. A number of enhancements to the envelopes and filters have been developed during this time in an attempt to accommodate these few airports, without compromising the overall GPWS effectiveness for all the other airport "normal" approaches. However, there remains a limited number of cases which are still not satisfactory and which persist 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
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