Originally Posted by
Easy Street
+1 to everything you and Wide Mouth Frog said.
I sincerely hope the NTSB can avoid being distracted by the distractions of altimetry and the missing ATC words on the Blackhawk CVR.
Upthread, Luca Lion calculated the 3 degree PAPI approach path as crossing the eastern riverbank at 270ft. If that's correct, then the CRJ's 313ft radar height 2 seconds before collision puts it at least 43ft above the approach path, so the Blackhawk's radio height deviation of 78ft would have contributed only about 35ft to the erosion of any intended "procedural separation" (*) between the aircraft. Or, to put it another way, the same outcome would have resulted if the Blackhawk had been at 235ft radio and the CRJ on the glide. Height keeping of plus or minus 35ft can only be achieved by instrument flying, which is obviously not compatible with visual separation (or indeed VFR) so cannot be reasonably cited as part of a safety case for the procedure. And of course a landing aircraft could easily be below the glide. Altimetry and height keeping are not the cause of this accident.
Missing the word "circling" wouldn't have influenced the helo crew getting visual with the CRJ at the time of the trasnmission. At best, it would have given them an extra nudge that "runway 33" (which was audible) meant the CRJ would be taking an easterly flight path. Missing "pass behind" with only a few seconds to collision was irrelevant if, as seems likely, the helo crew did not see the CRJ at that point.
(*) The quotes around "procedural separation" are intended to convey a tone of disgust and sarcasm.
Following "5*why", keep asking...
Why did the did miss part of the message
Why was the incomplete read back missed
Why does missing a few words lead to this disaster within seconds.
Does this lead an answer like: helicopter in a very busy airspace, busy controllers (insufficient time to be fully focused on full read backs) being by default too close to (and even needing to cross) the glideslope.