Show HN: Airline pilot's interactive guide to aviation radio | Hacker News Reader

Show HN: Airline pilot's interactive guide to aviation radio

jameshard.ing

3 pointsjamesharding8 comments

Hey HN! I'm an A350 pilot, some of you might remember my flying stats page from last year.

Most people assume modern airliners navigate purely by GPS. In reality we still lean on a whole stack of ground-based radio navaids (VOR, DME, NDB, ILS) the oldest of which trace their lineage back to the 1920s.

With the amount of GPS jamming around the world at the moment, there are regular stretches of a flight where the jet falls back to these older systems to work out where it is.

I first learned all this from a textbook full of static diagrams, and always thought it deserved better. So I built interactive, draggable animations for each one — VOR, ILS, DME, TCAS, SELCAL, phased arrays and more.

Happy to answer any questions about the tech or the flying! :)

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Here was my interactive logbook post from last year for those interested: https://news.ycombinator.com/item?id=44396518

I have a question related to aviation though not the submission itself please.

How often would you say you get to do a non-ILS landing? I often wonder how common these are outside of North America (where I hear visual approaches are apparently way more common than in Europe).

And related to that, how often do you see VOR approaches in the wild?

Valid question!

The vast majority of approaches are still using an ILS. Pretty much the only time we would use an alternative approach (most often RNAV or LPV, and rarely VOR) would be if an ILS is not available.

That said, in the US especially, controllers are quite keen to offer a "visual approach" as it then relieves them of the duty to maintain separation from the aircraft in front. This is a cultural thing in the US, and the rest of the world does not operate this way. Even when flying a "visual approach" in the US, the ILS is usually still radiating, and we often still fly the approach using the autopilot coupled to the ILS, just maintaining our own separation from other traffic visually.

As for VOR approaches, I have done a handful in my career, especially into some of the smaller airports around Europe (Greek islands!), but these are gradually also being replaced with RNAV approaches generally.

On the A320 which I flew at the time, even VOR approaches were flown using a coded approach path, with the VOR needle itself being used for crosschecking. In the sim, we fly them still to make sure we remember how to, but they are quite rare these days!

Thank you!

I love learning about nav aids on planes. One thing I didn't quite understand was the DME interrogation: "To handle conflicting pulses, each aircraft deliberately jitters its interrogation timing at random, then keeps only replies at a constant lag after its own pulses."

Does this mean that the pulse pair itself was jittered? As in, plane A sends a pulse pair, say 10us between the pulses and plane B sends a pulse pair 20us apart. The DME then responds with the same pulse pair delay and the planes listen then calculate the responding pulse pair to figure out which one is theirs?

The pulse pairs themselves are always 12 us apart. The jitter comes from the aircraft sending interrogations at random intervals in a steam, so that it can discern which returns are at at the same interval as the ones that were sent. I can make the animation more obvious for this -- on my to do list :)

Oh, now that makes more sense, thanks!

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