Sunday, January 28, 2007

Flying RNAV Departures

My apologies for the long break from blogging. This was due mostly to my getting sick and then having a spate of unplanned maintenance activities on my Jetta TDI. We're both now in fine fettle, thank you, though I'm a bit poorer than I'd like. These recent events have led me to offer some unsolicited testimonials:

Bauer's European Auto Repair in Berkeley - they actually understand diesel engines, they're friendly, and their prices are reasonable, and they don't treat you as if you're in league with the devil if you are using biodiesel.

Zicam Cold Remedy Rapid Melts - a homeopathic cold remedy recommended to me. I was skeptical until I tried it. While it doesn't make your cold go away, it turns the volume down on the symptoms and helps you get on with your life.

Mucinex - a time-release, tablet version of guaifenesin (a common active ingredient in cough syrups). It's better than cough syrup by a long shot.

Now on to the promised discussion of RNAV departure procedures. RNAV departures in the U.S. are designed primarily to simplify the delivery of IFR clearances in busy airspace, to provide obstacle clearance in remote areas where VOR reception is spotty due to terrain, or both. They come in a couple of flavors: Type A and Type B. Both types usually start with a heading or vector from the end of the departure runway to an RNAV fix. The differences between type A and B SIDs are largely incidental to the pilot flying with a 430W or 530W, but here they are for completeness:

First RNAV fix from the end of the departure runway:
Type A: approximately 10NM
Type B: "near" the departure end

RNAV accuracy required during 95% of the flight time:
Type A: +/-2NM
Type B: +/-1NM

Altitude Engagement:
Type A: no later than 2000 feet Height Above Airport
Type B: no later than 200 feet HAA

Equipment required (described in AC 90-100)

There's really not a lot to flying a RNAV SID, as long as you do some preflight planning. The first task is to ensure that you can meet any required climb gradient specified on the chart. Consider the CHOIR ONE departure from Alturas, California.

And I shouldn't have to say this, but:

Don't use any of the charts, snippets, or other illustrations shown in this blog for navigation in a real aircraft.

This SID requires a minimum climb of 367 feet per nautical mile or 389 feet per nautical mile, depending on the departure runway, up to 11,000 feet. The climb gradient is expressed in feet per nautical mile because the procedure designers don't know how fast your particular aircraft is traveling in a climb. Here's a snippet from an old Klamath Falls VFR sectional showing the topography around Alturas.

Jepp charts are kind enough to calculate the required climb rate for you, translating the climb gradient into feet per minute for a range of different climb speeds. If you use FAA charts, you can use a table in the front part of the approach booklet to do the conversion or just use your calculator:

(398 feet/NM X 100 NM/hour)/60 minutes/hour = 648 feet/minute

This climb rate at altitudes above 6,000 feet MSL is beyond the capability of many single-engine GA aircraft, so check your aircraft's flight manual. If you're flying a multi-engine aircraft, of course you'll want to look at the single-engine rate of climb performance, just in case.

Next, you'll want to do either an FDE prediction and/or a RAIM prediction prior to departure. Power up you Garmin GPS, bring up the Auxiliary pages, find RAIM prediction, and tell the unit to do it's thing. Remember that RAIM prediction uses a satellite almanac to predict the number of satellites your GPS antenna should be able to see, but it is not a guarantee that the in-flight RAIM calculations that the receiver makes will always succeed. Translation? Your RAIM prediction could succeed, but you could still get a RAIM failure in flight (though it is unlikely).

Since a pre-flight RAIM prediction is so important, why does Garmin insist on burying this feature, requiring a bunch of knob twisting and button pushing?

For this example, we'll do a trip from Alturas to Reno, Nevada using the CHOIR ONE departure, then direct to a fix on the RNO RNAV 16R approach. Press the FPL button, press the small knob on the lower right to enter cursor mode, scroll to the empty space below KAAT, then turn the small knob to spell out KRNO for Reno.

Press the PROC button, then scroll with the big knob on the lower right, highlight SELECT DEPARTURE, and press ENT. Select CHOIR1 from the list, and press ENT.

On departure, you can use the terrain view to give you an idea of where the obstructions are located as you climb.

As you approach the second waypoint, the 530W will give you a 10 second countdown before you need to change heading.

As you approach CHOIR, you'll get the same 10 second countdown, then the unit will tell you to turn. As I've said before, this countdown and turn instruction are a huge improvement from the earlier 530/430 units where the prompt was so short lived that it was easy to miss. Turn when the unit tells you to turn and you'll fly by the waypoint and get established on the airway without overshooting.

In a future installment, I'll cover flying a STAR.


Colin Summers said...

My comment is off topic, sorry. At least it is about instrument flying, though.

On Thursday I flew up to CCR from SMO, right into your neck of the woods. The Norcal Approach controller said CCR was LIFR, but that people were getting in, so we decided to give it a shot. We had a little airport nearby as our VFR alernate.

Norcal said to expect the VOR approach to 19R when we asked.

Transferred to Travis Approach they asked if we were on the LDA approach, and we said Norcal had said CCR was using the VOR. They said okay.

The tower was surprised, and said the last controller (Travis?) said we were on the LDA. They sounded put out. We were a little high, but landed uneventfully (I *love* uneventful landings).

As a newly minted IFR pilot:

a. If we had switched to the LDA approach when Travis said they thought we were on it, would Norcal have been confused and run a bizjet into us somehow?

b. Does this sort of confusion happen often? It's not a good feeling when it seems like those guys in the little rooms aren't really coordinated.

most importantly, since you are the Bay area airport IFR expert:

c. Why is it an LDA approach? Approach course is 181 and the runway is 19R, a difference of less then ten degrees. I can't find the definition online, but I thought LDA had to be considerably further off, no?

Thanks. Frequent reader, occasionally flyer.

John said...

Hi Colin,

You ask some excellent and reasonable questions.

First off, Travis Approach controllers are military controllers and many of them are "in training." It's not uncommon to get a slam-dunk vector into Concord but I think it's more a reflection of the controllers' lack of skill than anything else. Sad, but true.

The coordination between Concord tower and Travis is, in my years of experience, sometimes excellent, usually mediocre, and on rare occasions it's downright awful (and dangerous).

The KANAN locator outer marker has been out of service for several weeks now and NOTAMed as such. You might have missed this in your pre-flight briefing:


The CCR ATIS has been saying lately "KANAN LOM is out of service, except for GPS-equipped aircraft." Not to be a stickler, but KANAN is out of service, period, though GPS-equipped aircraft can use GPS in lieu of ADF to identify KANAN. This is what I think they are trying to say in the ATIS. The AIM is pretty clear about GPS substitution in these cases: "The ground-based NDB or DME facility may be temporarily out of service during these operations."

Because KANAN is out of service, I think they have been saying that the VOR 19R approach is in use by default. They still allow the LDA approach for GPS-equipped aircraft and you can, and should, request the LDA approach if the ceiling is less than 1000' or the visibility is low and you are GPS-equipped.

The Concord tower should not release another aircraft to depart IFR regardless of the approach for which you have been cleared. Due to terrain surrounding the airport, all IFR departures out of Concord head toward the CCR VOR or KANAN, so they would be opposite direction for any aircraft inbound on any approach into Concord.

When you get your IFR approach clearance into Concord and the field is IFR, the class D airspace is yours and yours alone until you either land or declare a missed approach. To paraphrase an old IBM system programmer's phrase: the IFR airspace in this case is a serially reusable resource.

Check your approach charts closely and you'll see the intermediate approach course for the CCR VOR 19R and the LDA 19R are not coincident. If you're cleared for one approach, I'd recommend against changing to another approach without clarifying it with the controller.

The poor coordination that you experienced between Travis Approach and Concord Tower happens all too frequently. If you're so inclined,
I'd encourage you to contact the manager at Travis Approach and tell him or her what happened. Be ready to tell them the date and time so they can pull the tapes and review them.

The CCR LDA 19R is an LDA approach and not a localizer approach because the localizer course is more than 3 degrees out of alignment with the runway.

I could tell you about my firsthand experiences with poor coordination between CCR tower and Travis that would curl your hair!

Anyway, hope that helps and I'm glad your approach and landing was uneventful.

John said...

I hate that VWs are so expensive to work on! And, I also hate that I get treated like some nut because I burn vegetable oil. It's always their first excuse to charge me more or why they can't fix my car. Too bad I am thousands of miles away from your shop.

John said...


Are you using biodiesel or have you converted your TDI to straight vegetable oil? The SVO conversion is too big a leap for me, but putting biodiesel in my tank instead of dino-diesel is pretty easy. Just wish I had a small supply of Jet-A I could add to the mix...

You may already know about this, but here's a link to a list of reliable, independent diesel mechanics who work on TDIs.

Eric Gideon said...

Another thing about RAIM (which is indeed stupidly hidden on the GNS series) is that if you punch in the current barometer setting, the unit requires one less satellite to detect isolate faults.

Not something I uncovered until I started working on my CFII this year, but I'm going to make it part of my before-taxi check.

John said...

Actually, I run waste veggie oil in an auxiliary tank. I have someone who I buy the filtered oil from, otherwise I probably would buy a hybrid. Thanks for that link!