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Old 16th Apr 2017, 21:35
  #1097 (permalink)  
GKaplan
 
Join Date: Apr 2008
Location: GB
Posts: 67
Originally Posted by [email protected] View Post
GKplan and others - I am basing my questions on the facts included in the interim report which many people seem not to have bothered to read before they post here.

If the IAAB have got their facts wrong then discuss the GPWS boundaries but I suspect it is unlikely that they have.
And I based my answers (copy and paste) on CHC Ireland's manual.
Should be fairly close...


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.
Actually in that case the AAIB isn't very clear, but I guess a footnote is not the most appropriate place to start copying a manual

This would have been a bit clearer: Mode 4B is active between 10 and 100 feet RADALT height with the gear down and speed above 80 knots. The upper boundary varies linearly from 10 feet at 80 knots to 100 feet at 120 knots or greater.

So (as ukv1145 rightly said), it is a height boundary not a forward one.

A confusion (as said before by others) exists in some minds between mode4 and 'look ahead'.

There is no relation between the look ahead (database) mode and the position of the gear. (and that answers your first question Crab. It is a yes, regardless of gear or speed. The remark about lowering the gear too early is not relevant).

Not selecting LOW ALT on the other hand might have given a mode 2 warning (not sure it would have been sufficient however, given the steepness of the island slope/cliff).

Last edited by GKaplan; 16th Apr 2017 at 22:03.
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