Readback: December 2019


Where is WAAS From?

In the August 2019 Readback, your reply to the writer who was referring to the “More ILS vs. LPV” article (February 2019) errs when you say that “GPS is a single receiver system for various satellites and WAAS ground station(s).” WAAS data is transmitted to users from geostationary communications satellites. Currently three geo comsats are broadcasting WAAS signals covering North America.

Jim Torley

Colorado Springs, CO

You’re absolutely correct. In that response we missed a step. WAAS signals do indeed reach the GPS receiver from satellites. The “WAAS ground stations” receive the raw GPS signal and determine a position correction that is then sent up to the WAAS satellites to be sent to your receiver.

Don’t Try This at Home

In the June 2019 issue, back cover, On the Air, Mr. Andrew Gray of San Diego tells a tale of (apparently intentionally) passing so close to and underneath an aircraft pointed out to him by ATC that he could “read their tail number and see the pilots’ faces.” I know this contribution was meant to solicit a chuckle, but don’t regs (and common sense/common courtesy/regards for safety) call for overtaking another aircraft by passing well off to the right? And should your publication be promoting such reckless antics?

Mike Pierce

Kerrville, TX

While most of the submissions for OTA are, indeed, based in fact, most are also embellished at least somewhat for their comedic effect. Of course, since we don’t know which is which, one shouldn’t take any story intended for OTA to illustrate techniques to be emulated.

That said, we don’t know from this particular submission just how close the two aircraft came. Perhaps one was IFR and the other VFR, and they could have legally come within 500 vertical feet, possibly with some lateral offset, which is definitely close enough to read a tail number and see pilots’ faces.

DA in lieu of MDA?

My friend was teaching someone and he called and asked me about the notes on a Jeppesen approach chart. Through ForeFlight I compared both Jeppesen and the government chart. The Jeppesen chart has a note that says, “Only authorized operators may use VNAV DA(H) in lieu of MDA(H),” but that note is not listed on the government chart.

I’ve looked through the TERPS and various FAA publications and I can’t figure out what this means. Help?

Dan Drew

Round Rock, TX

Okay, first, understand the difference between a DH and an MDA. The DH is the minimum altitude on a vertically guided approach, and it’s the point at which you must make a land/miss decision when on glide path. If you miss, you will go a bit below the DH and that’s permitted. An MDA, on the other hand, is a hard deck that can’t be penetrated without stuff in sight per 91.175.

With the advent of GPS approaches, and the ability of our magic wonder boxes to provide calculated vertical paths, many approaches with an MDA, such as this one, can be flown with a pseudo glideslope. In this case the approach you’d load would be an LNAV+V. That’s not FAA-recognized vertical guidance, but most boxes provide it anyway as supplementary information.

Some certificated operators, however, are authorized to fly certain MDA approaches to a DH, in some circumstances. When that’s true, Jeppesen places that note on the chart telling us non-certificated operators that we must still use the MDA. It’s really kind of superfluous. Without that note we’d simply fly to the MDA anyway, and that’s probably why the FAA has no such note.

Not Catching Enough Zzzz’s

In the August issue, the last OTA mentions a crossing fix of OZZI. I am not familiar with that part of the country, but also not familiar with 4-letter fixes. If it is a VOR it would be 3-letters and if an intersection it would be 5-letters.

What am I missing here?

Barry McCollom

Kerrville, TX

An extra z: OZZZI.

Avoid That Fruit

ATC reroutes you around a watermelon? (Reference the graphic on page 9 of the August issue in “Going Around Weather.”)

George M Tamayo

Bullhead City, AZ

Yup, kinda looks like it, eh?

Wants to Build a Sim

Your September article, “Certified Sim vs. DIY” piqued my interest in building a home-grown sim. Will you be writing about how to do it? That is, what hardware and software works well, where to source needed items, etc.? I think non-certified is the way to go. If you have some tips on where to start, I’d love to hear them.

I’m flying a PA-30 and a Lake Renegade, both well equipped, but like many don’t get more than a few real IFR days all year.

Frank Bell

Hendersonville, NC

Well, you’re somewhat in luck. See Page 9 of this issue to get started. While this article doesn’t address the parts and pieces, or where to get them, it does cover a lot that any prospective sim builder should think about before spending any money.

Will we cover those parts and pieces in the future? We currently have no plans to do so largely because the market is so big and varied. For example, if we wanted to review just the flight controls, we’d need an article on the yoke, one on rudder pedals, then another on the power quadrant.

That’s not to say that if we come across some stunning components we wouldn’t write them up. So, never say never…

Canadian ADS-B Dilemma

We are located in Buffalo, NY, so flying to Canada is a definite factor in deciding how to equip with ADS-B. I have been researching diversity and compliance options since NAV CANADA’s decision to require diversity was first mentioned. “Canada’s ADS-B” in your October issue was the definitive primer.

Early on it was evident that 1090ES was a preferred solution. NAV CANADA’s Phase 1 and 2 are pretty straightforward—if you are flying above 12,500 feet in their class A or B airspace you’ll need a diversity transponder with ADS-B.

But, there is not a lot of information out there about what Canada’s Phase 3 will require. Lots of uncertainty and lobbying by pilot groups and manufacturers could result in changes. Time may also bring lower-price diversity options to market. We have been holding off on equipping our U.S. low-and-slow birds and the decision can’t be delayed any longer.

I hope you can provide some guidance. Currently, the majority of our flights to Canada are close to the U.S. border. I can’t recall not being in radar contact with a Mode C transponder. So if NAV CANADA plans on implementing some ground-based stations, they will in all likelihood be in more populated areas close to the border where radar coverage exists today. If this is the case, my theory is that they will receive our ADS-B out from our U.S.-based aircraft with 1090ES without diversity.

What do you think?

Thomas Santulli

Buffalo, NY

We were told that not long ago, Canada’s Phase 3 was also defined. But, due to the pressures you describe, they’ve backed off and the requirements of Phase 3 at this time are unknown.

But, let’s speculate. You should keep in mind that NAV CANADA is a majority stakeholder in Aireon and satellite-based ADS-B. This means they’ll want to protect and justify that decision and expenditure.

Also note that today’s ground stations that receive Mode C transponders are not, unless modified, capable of decoding the ADS-B information from an equipped aircraft. Meaning, that if NAV CANADA wants to receive any ADS-B on the existing radar, those systems will have to be modified. Since they’ve made the decision to use ADS-B from satellite receivers, why would they also support ground-based receivers? That expenditure could well be political suicide.

But, with enough pressure, it’s probably far more likely that Phase 3 will include some ADS-B exemption, at least for a time, for aircraft flying within range of the normal ground-based radar. Given that ADS-B is largely for surveillance, perhaps non-ADS-B traffic at low altitudes within, say, 50 to 100 miles of existing ground-based radar could be exempted. This would seem to be a reasonable compromise that would meet most everyone’s requirements. But there’s no way of intelligently guessing at this point.

To fly both in the U.S. and in Canada, your options are limited: Either equip cheaply for the U.S. now, and wait to see what develops in Canada’s Phase 3, or equip with a diversity transponder now and be done with it.

The cheap-now option is appealing and lets you fly in the U.S. and, at least for the next few years, in Canada. If NAV CANADA never requires the kind of flying you do to have ADS-B, you’re done. If Canada does require your aircraft to have diversity 1090 ES, then junk the cheap-now option and, as you say, full diversity equipment will surely be cheaper by then. You’d most likely still be in it for less total money than had you installed a diversity 1090 ES solution today.

Of course, this is just ADS-B Out. If you want ADS-B In (U.S. only), you’ll need to consider either a portable solution in addition to the installed one, or you’re back to the diversity 1090 ES transponder that also receives ADS-B In.

Good luck. Please let us know what you decide.


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