Nav Course in India

Prof. H.B. Hablani from Dept Aerospace Engrg, Indian Institute of Technology (Bombay) recently taught a 5-day course on integrated navigation, based primarily on Integrated Aircraft Navigation and augmented with others (including my 2007 book).  He has approved my quoting him as saying “both books are of very high quality, unique and original.”

In 2013 a phone presentation was arranged, for me to talk for an hour with a couple dozen engineers at Raytheon. The original plan was to scrutinize the many facets and ramifications of timing in avionics. The scope expanded about halfway through, to include topics of interest to any participant. I was gratified when others raised issues that have been of major concern to me for years (in some cases, even decades).  Receiving a reminder from another professional, that I’m not alone in these concerns, prompts me to reiterate at least some aspects of the ongoing struggle — but this time citing a recent report of flight test verification

The breadth of the struggle is breathtaking. The About panel of this site offers short summaries, all confirmed by authoritative sources cited therein, describing the impact on each of four areas (satnav + air safety + DoD + workforce preparation). Shortcomings in all four areas are made more severe by continuation of outdated methods, as unnecessary as they are fundamental, Not everyone wants to hear this but it’s self-evident: conformance to custom — using decades-old design concepts (e.g., TCAS) plus procedures (e.g., position reports) and conventions (e.g., interface standards — guarantees outmoded legacy systems. Again, while my writings on this site and elsewhere — advocating a different direction — go back decades, I’m clearly not alone (e.g., recall those authoritative sources just noted). Changing more minds, a few at a time, can eventually lead to correction of shortcomings in operation.

We’re not pondering minor improvements, but dramatic ones. To realize them, don’t communicate with massaged data; put raw data on the interface. Communicate in terms of measurements, not coordinates — that’s how DGPS became stunningly successful. Even while using all the best available protection against interference, (including anti-spoof capability), follow through and maximize your design for robustness;  expect occurrences of poor GDOP &/or less than a full set of SVs instantaneously visible. Often that occurrence doesn’t really constitute loss of satnav; when it’s accompanied by history of 1-sec changes in carrier phase, those high-accuracy measurements prevent buildup of position error. With 1-sec carrier phase changes coming in, the dynamics don’t veer toward any one consistent direction; only location veers during position data deficiencies (poor GDOP &/or incomplete fixes) and, even then, only within limits allowed by that continued accurate dynamic updating. Integrity checks also continue throughout.

So then, take into account the crucial importance of precise dynamic information when a full position fix isn’t instantaneously available. Take what’s there and stop discarding it. Redefine requirements to enable what ancient mariners did suboptimally for many centuries — and we’ve done optimally for over a half-century.  Covariances combined with monitored residuals can indicate quality in real time. Aircraft separation means maintaining a stipulated relative distance between them, irrespective of their absolute positions and errors in their absolute positions. None of this is either mysterious or proprietary, and none of this imposes demands for huge budgets or scientific breakthroughs — not even corrections from ground stations.

A compelling case arises from cumulative weight of all these considerations. Parts of the industry have begun to address it. Ohio University has done flight testing (mentioned in the opening paragraph here) that validates the concepts just summarized. Other investigations are likely to result from recent testing of ADSB. No claim is intended that all questions have been answered, but — clearly — enough has been raised to warrant a dialogue with those making decisions affecting the long term.


The sky isn’t falling but some of our bridges are. About seventy thousand of them are structurally deficient, and about a quarter of those could go at any time. Calamities are sure to mount if nothing is done. The number that will occur (e.g., after belated prevention efforts) is unknown.

That number could be reduced by a method not currently in use. In combination with other steps (placement of sensors at strategic locations on a structure) a historical pattern of deformations can be generated automatically. The means of analyzing the deformations has already been shown to provide early warning capability, via application to data recorded before the 2011 Tohoku earthquake. There is no need to repeat the description here; it’s already documented.

Sooner or later another subject comes up: The “C” word (cost). Aside from severity of the problem, about the only other item prompting agreement is the notion that a solution is unaffordable. Let me change that notion this way: if a complete solution is deemed unaffordable, a partial solution doesn’t have to be. Prioritize. Bridges exhibiting the most urgent warning signs are highest priority for remedial action. At 1/70,000th of the total cost, no one could reasonably refuse to fix one that must be fixed.

An acknowledgment: the argument just cited is overstated. Initial investment is always a greater fraction of the long-term total, and applying a method for the first time to any operation requires ironing out some wrinkles. Still, admitting that a fraction exceeds 1/70,000 doesn’t constitute a shocking confession. The sensors don’t have to be top-of-the-line. If the “bottom line” is all that matters, then here’s the real bottom line: Their cost, plus the cost of a government-sponsored project, pales in comparison with losses resulting from a bridge collapse — let alone the losses incurred from seventy thousand collapsed bridges.

John Bortz

In February of this year the navigation community lost a major contributor to navigation — John Bortz. To many his name is best known in connection with “the Bortz equation” which easily deserves a note here to highlight its significance in development of strapdown inertial nav. Before his work in the early 1970s, strapdown was widely considered as something with possible promise “maybe, if only it could ever come out of the lab-&-theory realm” and into operation. Technological capabilities we take for granted today were far less advanced then; among the many state-of-the-art limitations of that time, processing speed is a glaringly obvious example. To make a long story short, John Bortz made it all happen anyway. Applying the previously mentioned equation (outgrowth of an early investigation of Draper Lab’s Dr. J.H. Laning) was only part of his achievement. Working with 1960s hardware and those old computers, he made a historic mark in the annals of strapdown.  Still, importance of that accomplishment should not obscure his other credentials. For example, he also made significant contributions to radio navigation — and he spent the lst two decades of his life as a deacon.