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Aviation is technology and change resistant. It’s all about certification, validation safety studies, and so on. Given the expected results, this is not that bad, but this also leads to strange perceptions. One of the hot topics these days is Required Navigation Perfomance, a.k.a. RNP.

The concept is simple: if a plane can fly with a precision of 1 nautical mile 99.99999% of the time, it can be certified as RNP-1. 0.3 NM ? RNP-0.3, and so on. Flying a precision approach requires an RNP-0.1 certification. The whole story is more complex, but I made it shorter for you: it’s GPS guidance.

Planes flying ILS approaches are guided by electronic signal to a precision of a few meters, and this can be done with autopilot or manual flying. So what is that crucial in flying RNP-0.1 ? 0.1 Nautical mile is 185.2 meters, and GPS can provide positioning with an accuracy of 3 to 30 meters. So what ?

Yes, there are integrity, and failure mode questions. But the same questions to exist with current systems. An aircraft flying down a valley on an ILS and suddenly losses its electrical power is in a serious emergency situation. A similar aircraft, flying the same valley but guided by GPS will have the same problems in the same conditions.

Now that instruments have been “virtualized” via glass-cockpits, and systems like “highways in the sky”, the navigation source no longer really matters. It can be GPS, ILS, DME-DME, inertial platforms, gnomes or elves, as long as it can be converted to lateral and vertical deviation signals, it can drive an ILS-like indicator and an autopilot.

Flying an RNP route is usually simpler as a traditional navigation, as points can be defined anywhere, independently from beacon locations, so the procedural aspect is no big-deal, emergency situations put aside.

So why is a plane flying a GPS-guided route with a precision 0.1 nautical mile a big event ? As a technical guy, I don’t see any big innovation in that. So to paraphrase Shania Twain: that don’t impress me much ! The only “magic” I can see in that it could be certified, given how picky (seen how polite I can be ?) the regulatory bodies can be…