points by namibj 1 day ago | 0 comments
Because rail is quite non line of sight and quite infrastructure defined pathing.
The automatic coordination system hit a fail condition; they neglected the fallback protocols that had rules for spacing determined to work reliably without the computer keeping real time supervision; they crashed.
This is in the way more like the Washington D.C. helicopter plane mid-air where some normalization of deviance got people to ignore automated protection systems.
If most involved had known the fallback protocols they would have refused to move/continue while the protocols were utterly neglected. At least with a robust safety culture active, ofc.
I think that's not quite accurate. Yes, there was a normalization of deviance. But it wasn't primarily that automated protection systems were ignored.
First, the systems on board both aircraft could not have saved them. TCAS resolution advisories are inhibited below 900ft AGL and aural traffic advisories are inhibited below 400ft AGL. The aircraft collided below that altitude. The system wasn't ignored, it just doesn't do much at low altitude. The RJ crew got a TA about 20s prior to the crash, but that's not something that would normally require evasive action (they're trained to act immediately on an RA, not a TA). They were set up for landing. It's hard to find any fault with them.
The RJ wasn't equipped with ADS-B In, and the helo's ADS-B Out was misconfigured since installation. ADS-B In could have alerted both crews almost a minute prior to impact. But it wasn't available.
Second, if you're referring to the tower: Yes, the controller did get an automated conflict alert, but he did not ignore it. He asked PAT-25 whether they had the RJ in sight and told them to pass behind it. This response wasn't good enough, but that's mainly attributed to the controller's high workload and time pressure leading to omissions.
A proper traffic advisory should have included azimuth, distance, direction of travel, and type and altitude of the conflicting aircraft, e.g.:
PAT-25, traffic ten o'clock, one mile, north-west bound, a CRJ descending through four hundred, circling approach to runway 33.
A proper safety alert should also include an action to resolve the situation, e.g.:
Traffic alert, PAT-25, traffic ten o'clock, one mile, a CRJ on final for runway 33. Advise you [descend/turn] immediately.
Either one might have prevented the accident. But when ATC gets busy, the reality of those calls often looks quite different than how they're described in a textbook. Combining local and helicopter control with 12 aircraft on frequency is just too much. Of course, that leads to routine conflict alerts (5 separate events in the 18 minutes leading up to the crash). Sure, nuisance alerts lead to desensitization (and the report discusses that), but here the workload seems to have been the bigger underlying factor.
Of course, this is far from the only contributing factor. The normalization of deviance that the NTSB actually found are that visual separation had become the primary way of separating helicopters from aircraft, helicopter crews reporting "in sight" when they hadn't positively identified the traffic yet, the tower trying to "make it work" rather than forcibly slowing operations down, etc.
That in addition to putting a helicopter route as little as 75ft below the approach path, the helicopter's altimeter being 100ft off (within spec!), the helicopter crew's use of night vision gogggles severely limiting field of view, helicopters and fixed-wing aircraft being on separate frequencies severely limiting the RJ crew's SA.
And perhaps most egregiously, the FAA ignoring the countless warning signs (15 thousand close proximity events over 3 years, are you kidding me?) Failing to fix the helo route, failing to reduce arrival rate (the request from Potomac TRACON wasn't forwarded due to being "too political"), failing to improve the tower's conflict alert software... People did not ignore automation, the regulators ignored lots of growing holes in the slices of Swiss cheese.