Originally Posted by
Chock Puller
According to the procedure map Route 4 (which seems to be the one they were closest to) is supposed to be flown at or below 200ft north of Wilson Bridge. The Radar plots that surfaced so far show the helicopter above 300ft. Even if they misset their altimeter they probably have a radar altimeter and a 75% difference in height should be apparent to a crew familiar with low-level flying.
I have never flown there but if there's regular helicopter traffic 150ft below an ILS or circling approach airline crews familiar with the airport might tend to disregard TCAS proximate traffic, etc. as normal backdrop chatter.
Even when flying behind similar aircraft on an ILS in daylight and good visibility it takes quite some time to see that preceding traffic is slowing down as it only starts to "grow" at an alarming rate when quite close. I have witnessed that twice, once caused by self and another time caused by mismatched speed instructions from ATC. I have resolved to never accept visual separation to preceding traffic at night and while the European aversion to visual approaches might be excessive, high density night ops based on visual separation don't seem to be a good idea even without that crash.