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How reliable is reliable enough?

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.


By James Farrell 09 May, 2023
A look back in time by James L Farrell, PHD - 2023
11 Apr, 2020
Apologies for little posting lately. Much activity included some with deadlines; this will focus primarily on the few years leading up to Covid.
11 Apr, 2020
GNSS Aided Navigation & Tracking
By James Farrell 30 Aug, 2018
Apologies for little posting lately. Much activity included some with deadlines; this will be limited to the past twelve months. In 2017 my involvement in the annual GNSS+ Conference again included teaching the satnav/inertial integration tutorial sessions with OhioU Prof. Frank vanGraas. Part I and Part II are likewise being offered for Sept 2018. Also...Read More
28 Jun, 2018
Once again I am privileged to work with Ohio University Prof. Frank vanGraas, in presenting tutorial sessions at the Institute of Navigation’s GNSS-19 conference. In 2019, as in several consecutive previous years, two sessions will cover integrated navigation with Kalman filtering.  Descriptions of the part 1 session and part 2 session are now available online. By way of...Read More
30 Apr, 2018
The Institute of Navigation’s GNSS+ 2018 Conference provides me the privilege of collaborating with two of the industry’s pillars of expertise. Ohio University Professor Frank van Graas and I are offering fundamental and advanced tutorials.  Then on the last day of the conference I’m coauthored with William Woodward, Chairman of SAE Int’l Aerospace Avionics Systems Division and hardware lead...Read More
24 Apr, 2018
A new SAE standard for GPS receivers is a natural complement to a newly receptive posture toward innovation unmistakably expressed at high levels in FAA and Mitre (ICNS 2018).  Techniques introduced over decades by this author (many on this site) can finally become operational. 1980s euphoria over GPS success was understandable but decision-makers, lulled into complacency, defined requirements in adherence...Read More
22 Mar, 2018
At April’s ICNS meeting (Integrated Communications Navigation and Surveillance) as coauthor with Bill Woodward (Chairman, SAE International Aerospace Avionics Systems Division), I’ll present “NEW INTERFACE REQUIREMENTS: IMPLICATIONS for FUTURE“.  By “future” we indicate the initiation of a task to conclude with a SAE standard that will necessitate appearance of separate satellite measurements to be included...Read More
16 Jul, 2016
A recent video describes a pair of long-awaited developments that promise dramatic benefits in achievable navigation and tracking performance.  Marked improvements will occur, not only in accuracy and availability; over four decades this topic has arisen in connection with myriad operations, many documented in material cited from other blogs here. 
12 Feb, 2016
For reasons, consider a line from a song in Gilbert-&-Sullivan’s Gondoliers: “When everybody is somebody, then nobody is anybody” — (too many cooks) For consequences, consider this question: Should an intolerable reality remain indefinitely intolerable? While much of the advocacy expressed in my publications and website have focused on tracking and navigation, this tract concentrates...Read More
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