Originally Posted by
ATC Watcher
We can close the discussion about EFVS then.
If the pleliminary ADS is correct , and if both were on Runway centerline, the vertical distance at 06:40:31 is quite worrying!
At 06:40:31, FDX had around 60fps overtake on SWA, with about ~750' horizontal separation and no vertical separation. FDX continued to close on SWA as SWA accelerated, and apparently overtook them at 06:40:41 or thereabouts, however they had commenced gaining a vertical separation from 06:40:33 or thereabouts. The vertical info is not readily available, but there would be a rate of at least 35 fps increase in vertical separation for an established G/A, and up to 60 fps with an aggressive G/A. (short term, emergency pull up can trade kinetic for potential, and you could achieve 100+fps readily non steady for short periods, but near the ground you are constrained in the pitch rate to not hit the tail initially when close to the ground, and you are rate limited in pitch for g margin to buffet, so the pitch rate is not going to be eye watering. rough figures are at the initial overtake, at 06:40:41 or thereabouts there was about 250' vertical separation at least. CPA would have been 2-3 seconds earlier, and was less than 200'. This is really really rough, but suffice it to say, it was a high risk event. The time based separation is less than 4 seconds, which is about the same level of unpleasant surprise as the Logan Airport loss of separation event that just occurred. 4 seconds below 150kts is not much distance, any way it is considered. CPA doesn't take int consideration the geometry of the aircraft structure around the static ports that the data is being measured at for altitude, and the GPS antenna location on the body that the ADS-B position is being derived from.
If the system as it stands cannot take the activity rate, then that needs to be reduced, which will call howls of protest, but protects lives. It is too small a sample set to say this is a new trend, but it sure is shaping up to be one, Austin, Boston, John Wayne...