How reliable is reliable enough?

 

GPS is by far the best-ever system for both navigation and timing. Recognition of that is essentially universal. Less widely recognized are the ramifications of growing dependence on GPS, in both communications and navigation. This discussion will concentrate on the latter, highlighting attendant risk in flight. Although extensive deliberation already exists, I’ll presume to offer my experience. Immediately it is acknowledged that the risk is low; but now let’s ask what is low enough. While every effort is made here to avoid an alarmist tone, answering that question calls for an unflinching look at potential consequences if the gamble ever failed.

The above paragraph opens a broader (two-page) discussion on this same site.  That expanded discussion addresses several familiar topics; GPS, for example, lives up to expectations, brilliantly performing as advertised. Since no system can be perfect, the industry uses firmly established methods, supported by widely documented successful results.

Backup for GPS, strongly urged in the widely acclaimed 2001 Volpe report, remains incomplete. Continuation of this condition calls to mind the Titanic or the 2008 financial fiasco. Meanwhile, shortcomings of GPS integrity tests are described and inescapably demonstrated by citing a document from the spring of 2000, plus history of flightworthiness improperly bestowed with proprietary rights accepted for algorithms and tests (rather than rigor advocated two decades ago; #57 of the publication list). A subsequently documented panel discussion shows the extent of unpreparedness in the legal realm.

While bending over backwards to acknowledge that disaster is unlikely, an unflinching look reviews potential though improbable consequences. The meaning of G in GPS suggests that “unlikely” isn’t enough.

Although this is old information, realization has not been widespread. Also, present plans for upgrading to Automatic Dependent Surveillance Broadcast (ADSB) raise new concerns (#83 of the publication list, plus various blogs on this site related to collision avoidance, runway incursions, … ). This dialogue is prompted by considerations of safety. Again, “low” likelihood combined with absence of a calamity thus far offers no guarantee. I advocate a revisit of this issue with all its ramifications.