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Old 16th Apr 2017, 18:32
  #1089 (permalink)  
Join Date: Apr 2008
Location: GB
Posts: 67
Originally Posted by [email protected] View Post
So, one question is - even if Blackrock had been in the database, would the EGPWS have alerted with the gear down at a speed of less than 80kts?

The interim report seems to indicate the look forward boundary is only 10' at 80 kts and only 100' at 120 kts with the gear down. At 120 kts the aircraft is travelling at more than 180 ft/sec and even at 75 kts it is doing over 110 ft/sec.
Are these boundaries reasonable for a helicopter at low level?

Perhaps the SOP for putting the gear down so early needs to be revisited.
If it had been in the database the short answer is yes.

"The system uses measured and predicted flight path data together with database information to look ahead for threats. The look-ahead area is based on ground track and flight path angle, corrected for any turns. It uses a 6 climb out angle so it is assuming a rate of climb to clear the obstacle or terrain of ten times the groundspeed (for example, 1000 feet/min at 100 knots groundspeed).
The system should give at least 30 seconds warning of any threat (that is, just over one mile at 120 knots).
Detection of a threat will generate a yellow threat caution area on the display, accompanied by a yellow TERRAIN or OBSTACLE caption on the ADI and a "Caution, terrain" (or "Caution, obstacle") aural warning. This aural warning is repeated twice, continuously at 7-second intervals, if the threat persists.
If the aircraft closes to within 20 seconds of potential collision, the display threat area and ADI captions change to red and the aural warning changes to a continuous "Warning, terrain" or "Warning, obstacle"."


What can be discussed I guess is the Mode 2 "excessive terrain closure rate" (just to repeat, a 'non-database' mode )

"This mode is designed to warn of excessive closure rates to terrain, primarily in the cruise. It uses RADALT height and rate to determine closure rate, but it also takes account of landing gear position, ILS information and airspeed. There are two submodes, 2A for the cruise and 2B for approach and landing.
Both submodes are inhibited if terrain data is of high integrity, in LOW ALT and in autorotation.
Otherwise, the modes are active below 300 feet AGL on takeoff and below 1200 feet AGL in the cruise

There are two boundaries, defined by RADALT height and closure rate. The inner boundary goes from 1600 feet/min at 30 feet to 1920 feet/min at 400 feet then up to 650 feet at 3120 feet/min. The upper ROD limit is 10000 feet/min. This boundary assumes a speed of 90 knots. As airspeed increases beyond 90 knots, the boundary expands from the 650 feet point to 1250 feet at 6000 feet/min, the upper height limit.
If the boundary is penetrated either horizontally or from above, an aural "Terrain, terrain" warning is generated together with the yellow TERRAIN caption on the ADI. If the flight path continues to penetrate the boundary, one second later a "Pull up" warning is generated together with the red PULL UP caption on the ADI. The warning will continue until the boundary is vacated.

Mode 2A is operational when the landing gear is up and height is above 30 feet.
Mode 2B provides a desensitised envelope for approach and landing. It is enabled with the landing gear down, if an ILS approach is in progress and the aircraft is within two dots of glide slope centre, and during the first 60 seconds after takeoff. The alert boundary is from 100 to 300 feet AGL; penetration of the boundary generates a single "Terrain" aural warning, repeated continuously, with associated TERRAIN caption on the ADI."

Just to be clear, when referring to vertical speeds the boundaries are defined by the RADALT rate of change (ie 'does the needle move fast?') rather than the actual aircraft vertical speed
GKaplan is offline