Scott Dunham (RDU)
(Top Gun)
04/05/17 07:52 PM
Re: Runway Status Lights

They're at a bunch of places.

First set was a partial installation at DFW, where they used to do a LOT more runway crossings before the end-around taxiways were built. The original concept kind of fell out of the ASDE-X surface movement radar system - it had a conflict detection feature for controllers that provided an aural alarm and red "do not cross" lines on their displays, but the conflict alerts only look ahead about 15 seconds at best. When an alert occurred, the controller had to figure out what was going on and which aircraft were involved, call the pilot, provide some kind of instructions, and hope it worked out.

When FAA showed us the prototype at DFW, I pointed out that the red lines really ought to be out on the airport, cutting out the intermediate controller delay and likely making the warnings more effective...especially when you only had 15 seconds to mess with. We incorporated that into a (2001!) safety recommendation letter to the FAA asking for ground collision warnings that went direct to the cockpit, and RWSL was developed as a result. They're automatically driven by an interface between ASDE-X and the airport lighting system. It's gotten pretty good reviews from crews, and has been cited as mitigating numerous ground incidents resulting from controller and pilot blunders.

Before you ask, the 15 second time was a compromise between crying wolf and going off too late. The system can only draw an inference about what's going to happen by watching what's been happening, and that's not easy on the ground. When an aircraft is approaching a hold-short line at a pretty good clip but the pilot is totally on it, all the system sees is an airplane approaching the hold short line with no signs of stopping...yet. When do you throw an alert that's likely to be "real" as opposed to "nuisance?" Not the easiest assessment to make on a reliable basis.

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