WANTED: PRECISE VELOCITY — UNMANNED or NOT

Recent and current posts have expressed concern, serious to anyone who envisions future air traffic prospects.  Those concerns stemmed from events preceding further developments adding more disquiet. Consider this “triple-whammy:

 * prospect for tripling of air traffic
* addition of UAVs into NAS
* ADSB methodology plans

Now add all implications of a headline from 2013:   GAO Faults DHS, DoT for GPS Interference/Backup Effort   in that year-end description a friend of mine (Terry McGurn) is quoted, saying “I don’t know who’s in charge.” That thoroughly credible diagnosis, combined with subsequent observations by father-of-GPS Brad Parkinson, crystallizes in many minds an all-too-familiar scenario with a familiar prospective outcome: The steps they’ve correctly prescribed “can’t” be implemented now. It’s “too late” to change the plan — until “too late” acquires a new meaning (i.e., too-late-to-undo-major-damage).

Historically this writer has exerted considerable effort to avoid dramatizing implications of the status quo. While straining to continue that effort, I feel compelled to highlight those implications related to air safety.

OK there will be no naming names here, but many with influence and authority do “not believe that the minimum performance required by the ADS-B rule presents a significant risk to the operation of the National Airspace.”  Here’s my worry:
* That minimum required performance allows ten meters/second velocity error
* Efforts to provide precise position therefore become ineffective within an extremely short time

 * What translates into collision avoidance isn’t present Lat/Lon but future relative  position accuracy
* Consequently the accuracy that matters isn’t in position but in velocity relative to every potentially conflicting object

 * Each of those relative velocities can be in error by 10 m/sec or more in more than one direction

 * Guidance decisions made for collision avoidance must be prepared in advance
* TCAS sudden climb/dives (which produced a news story about screaming passengers), plans a minute and a half ahead
* With 10 m/sec velocity error that gives 900 meters uncertainty in projected miss distance —  just simple arithmetic
* That simple calculation is very  far from being a containment limit
* Only containment limits based on conservative or realistic statistics  can provide confidence for safety

 * 3 sigma (even 10 sigma) containment limits don't give low enough collision probability with non-gaussian distributions

Combined weight of these factors calls for assessment of prospects with future (tripled) air traffic plus UAVs. It has been asserted that, rather than ten m/sec, one m/sec is much more likely. As noted earlier, “much more likely” is far from sufficient reassurance. Furthermore, multiplying time-to-closest-approach by 1 m/sec, and amplifying that result by enough to produce a credible containment limit, still produces unacceptably large uncertainty in projected miss distance. So: expect (1) either frequent TCAS climb/dives or (2) guidance commands generated for safe separation resulting in enormous deviations from what’s really needed. Forget closer spacing.

Add to that runway incursions, well over a thousand per year and increasing — also with everything said about needs for avoiding other objects applicable to maritime (shoals) as well as airborne conflicts; Amoco-Cadiz, Exxon-Valdez, …  .

These points are covered by presentations and documentation from decades back.  The best possible sense-&-avoid strategy is incomplete without precise relative (not  absolute) future  (i.e., at closest approach, not current) position — which translates into velocity accuracies expressed in cm/sec (not meters/sec).  The industry has much to do before that becomes familiar — let along the norm that containment requires.  A step in this direction is offered by in-flight results validating the accuracy traits just described.