Thursday, March 29, 2012

Big Turn, Little Turns, Big Turn



DME arcs can be problematic for infrequent IFR flyers because, like holding patterns, arcs are not that common. A DME arc simply involves flying a circular course around a VOR/DME or VORTAC station (aka the station) at a specified distance, as if the aircraft were attached to the station on a string. Distance Measuring Equipment (DME) onboard the aircraft displays the distance from the station, though an certified GPS receiver can substitute for DME. It's easy to visualize a DME arc if you have a moving map and many late-model GA aircraft with fancy GPS units will fly a DME arc on autopilot while you sit back and watch. Without a moving map, joining an arc and tracking it accurately is more challenging, but it can be an enjoyable challenge. To that end, here are well-tested techniques for flying DME arcs, with or without GPS.

Anatomy of an Arc

The primary protected area around an arc is quite large (4 miles either side), but during a check ride or proficiency check pilots are expected to remain within one mile of the specified arc distance. Approaches incorporating a DME arc will have at least one minimum altitude to maintain, but altitude step-down fixes may be defined at particular radials along the arc.
DME arc Required Obstruction Clearance


Instructors and examiners often use the term right arc for an arc that keeps the station on the right wingtip of the aircraft, or left arc where the station stays on the left. Air traffic controllers usually refer to the general direction from the station where you will fly the arc, such as "arc Southeast." I've see at least one approach chart use the phrase arc clockwise. With calm winds, the station should remain directly off the wingtip. 

Remote, non-radar environments tend to have instrument approaches that use DME arcs because they help air traffic controllers who lack radar to maintain separation between aircraft. I saw a lot of approaches with DME arcs flying in the Caribbean for that very reason. Arcs also allow pilots to fly on their own navigation and get established on an approach course from en route environment. Consider the KLOL VOR/DME-A approach where you could be arriving via the Lovelock 219˚ or 054˚ radial, which happens to correspond to Victor 6.




Get Ready, Get Set ...

From a proficiency standpoint, flying a DME arc demonstrates your ability to plan and maintain orientation. Here are the basic steps.
  1. Get established on the correct radial leading to the arc
  2. Fly toward the arc
  3. Turn approximately 90 degrees onto the arc
  4. Maintain orientation as you track the arc
  5. Depart the arc on the appropriate radial
More simply, flying a DME arc consists of:
  • Big turn
  • Several small turns
  • One last, big turn

Consider the three basic navigation equipment set-ups found in most GA aircraft:
  • Two CDIs (Course Deviation Indicators)
  • One HSI (Horizontal Situation Indicator) and one CDI
  • One HSI and one RMI (Radio Magnetic Indicator, G1000's call it a bearing pointer)

If you have two separate VOR receivers, set one to navigate to the arc and the other to the fly the radial or course you'll use to exit the arc. Early editions of the FAA's Instrument Flying Handbook cautioned the reader that DME arcs should not be attempted without an RMI/bearing pointer. That wording was removed several years ago.

Tune your DME to the correct station and identify the Morse code id, remembering that these identifiers are broadcast just twice a minute. Beware of DME units that automatically use a frequency tuned on one of your VOR receivers, sometimes called remote channelling, because it's easy to inadvertently get distance information from the wrong station. When possible, consider manually tuning and identify the DME frequency. If you're using an IFR-approved GPS receiver to fly an arc, you have several options covered later.

Fly to the Arc

In the example shown, the aircraft is Southbound, tracking inbound on the CEC 343 radial toward the 11 DME arc. You could set HSI course pointer is set to exit the arc on the I-CEC localizer with the course needle set to 114 degrees and set the #2 CDI is set to fly to navigate around the arc. In this example the aircraft is headed TO the station to join the arc, but other approaches may have you headed FROM the station to join an arc. The first common mistake pilots make is they lose track of the station's position relative to their aircraft. Don't let this happen.



Some folks get all wound up about whether the radial should be at the top or bottom of the CDI. Keep it simple: Set the top of the OBS so it matches the general direction you need to fly to join the arc, in this case 163 degrees. For an HSI, set the course pointer so the arrow generally points in the direction you need to fly.

The Big Turn

Do yourself a big favor and get established accurately on the arc from the get-go. If you blow through the arc by turning early or late, you've made a lot of work for yourself and you're more likely to bust the 1 mile tolerance. It may sound simple, but you need to clearly understand which way you'll be turning initially to join the arc.

Approach charts are oriented North-up and if you're a Track-up person, the chart representation can seem upside-down: There's no shame in rotating your approach chart to a track-up orientation to help you visualize your situation.



With the chart oriented Track-up, it's obvious you want to turn right and keep the station off the left wing. If you're flustered or task-saturated and you simply guess, you have a 50-50 chance of getting it right. You certainly want better odds than 50-50 when flying in the clouds, right?

Many pilots recall a DME arc as being a series of small turns, forgetting that the initial turn onto the arc requires a big turn - roughly a 90 degree turn. You need to turn right, so look at the heading at the three o'clock position of the HSI or CDI. In this case, you'll be turning to a rough heading of 253 degrees. If you have a heading bug, bug that heading.

A 90 degree change in heading at 3 degrees-per-second takes time so you must to lead the arc to account for the distance covered during the big turn. A rule of thumb is to use 0.5% of your groundspeed as the lead distance. Assuming your ground speed is 120 knots, start turning onto the arc about 0.6 miles before the arc or when the DME reads 11.6 miles. Depending on winds aloft, your groundspeed may differ significantly from your indicated airspeed, so select the groundspeed readout on your DME and pay attention to it. When your DME reads 11.6, make the big turn.

After the big turn, the course pointer points to station


Turn Ten, Twist Ten

Regardless of which way you turn to get on the arc, stay on the arc by making a series of small, strategic changes in heading while adjusting your OBS or HSI to track your progress. Let's say you are using an HSI to fly the arc, twist the OBS so that you just barely have a full-scale needle deflection in the direction you are flying. Not sure which way to twist the course pointer? It's really simple, same side safe:
  1. Determine your current heading
  2. Locate that heading on the OBS or HSI
  3. Twist the OBS or HSI course pointer so the needle deflects on the same side of the CDI as where you found your current heading
Current heading on same side as course deviation bar = Same side safe


Using an RMI/bearing pointer is much simpler: Just adjust your heading to keep the arrow head of the pointer generally aimed at the station.

While you fly the arc, consult your DME to determine your distance and speed relative to the VOR/DME station. By setting the DME unit to ground speed/time-to-station mode, you can strive to see a ground speed (relative to the station) that is below 20 knots or so. That's taxiing speed and you won't get too far off the arc at those speeds.

If you have a heading bug, use it to track your chosen heading and adjust the bug each time you change heading to remain on the arc.

Let's say after joining the arc the DME indicates 11.2 miles. You're outside the arc and need to turn at least 20 degrees toward the station. Don't be afraid to make an aggressive heading change if you are outside the arc. On the other hand, if you joined the arc and the DME indicated 10.5 miles you are slightly inside the arc and that's not a bad place to be. Maintaining the current heading which should eventually take you back onto arc or turn away from the station by just 10 degrees. Wait 5 or 10 seconds and you should see the DME distance increase.

If the DME distance is within 0.1 or 0.2 miles, fly your present heading and wait for the CDI needle to center. Once it does, twist the OBS another 10 degrees, and consider turning the aircraft 10 degrees toward the station. Whether or not you change heading depends on the winds aloft and what the distance readout says.

Stop the Arc, I want to get off ...

To exit the arc on the desired radial or course, you need to make another big turn. Many instrument approaches with DME arcs depict a lead radial to alert you that your exit is approaching. Just like the turn to join the arc, exiting the arc require approximately 90 degrees of heading change.

This bring up the fact that there are four basic DME arc variations:
  • Fly TO the station, join the arc, exit the arc flying TO the station.
  • Fly TO the station, join the arc, exit the arc flying FROM the station.
  • Fly away FROM the station, join the arc, exit the arc flying FROM the station.
  • Fly away FROM the station, join the arc, exit the arc flying TO the station.

Additional Challenges

There are many places (the SF Bay Area being one) where there are few published DME arcs. That means a pilot on a check ride or proficiency check may be asked to demonstrate a made-up DME arc with no charted representation. When flying a made-up arc, your examiner or instructor should have specified either a left arc or a right arc, so figure out which way you'll need to turn to keep the station on the left or right side of the aircraft.

A particularly challenging DME arc can be found in the MTN VOR/DME RWY 15 where you arc right to the runway threshold, complying with various step-down fixes as you go. You'd obviously want to fly this arc very accurately. And if you need to fly the missed approach, you get to fly another arc to the missed approach holding waypoint. I've only flown this approach on a simulator, but would welcome the opportunity to try it in a real aircraft.


The Easy Way

If you're using an IFR-approved GPS receiver to fly an arc, here are your options:
  • Load the instrument approach defines the arc, specifying the appropriate transition
  • Make the VOR/DME station the current waypoint (proceed direct-to)
  • G1000 and G530 can display distance to any VOR station that has been tuned
The obvious choice with most late-model GPS receivers is to load the approach with the appropriate arc transisition and let the GPS guide you.



Practice Makes Perfect

The best way to maintain proficiency with DME arcs is to practice in a simulator or in a real aircraft. Like a good crosswind landing, there's a satisfying feeling to flying a good DME arc. Try it, you'll like it.

Saturday, March 24, 2012

Jepp MobileFD Matures, Slowly


As a company, Jeppesen is an enigma. A division of Boeing with a long history of quality and innovative chart products, they seem to have been dragged, kicking and screaming, into the EFB revolution. Jeppesen was a year late to the iPad EFB app party and while the latest update to MobileFD adds cool features, Jepp is so far behind their competition it's embarrassing. Still, the latest release does add some value to an already pricey app.

No-no, Geo-Ref

The most obvious feature that Jepp users have been waiting for - geo-referenced approach procedures - is still not available. You can get geo-referenced airport diagrams, so it obvious that Jepp knows how to provide this feature, they just haven't. And that makes the situation even more puzzling.

Rubber-Band, Man!

With the latest version you can do route planning with taps on the en route chart. The you can change your route on the same en route chart with rubber-banding - Tap, drag, drop to re-route. A dialog will appear with the available waypoints.



Chart Printing

Jeppesen has done something fairly radical (for them) in this release: Users now have the ability to print approach charts, SIDs and airport diagrams directly from the iPad without having to install and use Jepp's infamously buggy PC software. Printing from the iPad is especially handy if you aren't a PC user (the CD-ROMs that Jepp sent with my MobileFD subscription were never opened). For my printing needs I use Printopia running on my MacBook Pro, which allows me to print from my iPad to my HP LaserJet 2015. It works like a champ.

DO NOT USE FOR NAVIGATION!


Other Enhancements

A new screen lock button prevents inadvertent screen input during critical phases of flight. Especially handy to prevent unwanted tap input while flying in turbulence.

Readers may recall my lamenting about the Clear button on the route window deleting everything; The route, origin, and the destination as well as the all the alternates. Jepp developers have done the sensible thing and Clear now just clears the route, which is a big improvement.



There's a new GPS status icon that is always visible near the top of the screen, but the maddening part is you have exit the app and to go to the iPad Settings to enable the GPS. What's more, there isn't just one setting, but two; one for en route position display and one for terminal (though you only get geo-referencing on airport diagrams). It's beyond me why the app can't just recognize when a GPS receiver is available and use it. Perhaps Jeppesen's larger customers don't want their flight crews using unapproved GPS receivers?






Once your GPS receiver is configured, you can proceed direct-to anywhere on the map by tapping, but the interface is quirky: Proceeding direct-to a waypoint actually alters the waypoints contained in the route; waypoints you may have spent a lot of time entering. Bummer about that. And try as I might, I couldn't find a way to activate a leg in the route. Jeppesen implementation of this commonly understood feature borders on the bizarre.



Documents in the Cloud

If you subscribe to Jeppesen's Document Management Service you can upload your documents and have them pushed to authorized devices via a proprietary cloud interface. You need to enable this feature in iPad Settings and then you'll see a login dialog appear in Jeppesen MobileFD. This document feature will be very useful for operators who need to distribute OpSpec manuals and other company documents, though one wonders how much that service costs. At any rate, the document cloud doesn't appear to offer much utility to the average GA pilot.

Uncertain Conclusions

Jepp MobileFD has the dubious distinction of being the priciest iPad EFB solution out there, yet it seems that Jeppesen is more interested in the Big Fish than the average instrument pilot. If you still must have Jeppesen charts, then this is what you have to work with. It ain't all bad, but Jeppesen certainly could and should offer more given the app's price tag.

Thursday, March 22, 2012

ForeFlight Mobile adds Documents




ForeFlight Mobile 4.4 has added a way to store and view PDF documents on the iPad. ForeFlight provides versions of popular FAA handbooks, parts of the Airport/Facility Directory previously not available in this app, and chart legends for download and manages those files just like a chart subscription. This ForeFlight video explains the documents feature in great detail.

Documents in ForeFlight Mobile from ForeFlight on Vimeo.



The document reader provides indexed documents and allows you to save bookmarks. Complex pages, like illustrations the one below from the FAA's Instrument Flying Handbook, can take a while to render (though they seem to render much faster on the new iPad) which may leave you with the impression that the page you selected is blank. Be patient and you'll see complex pages appear.



You can download and store enhanced Class B representations. Unlike SkyCharts Pro, ForeFlight still doesn't provide important Terminal Area Chart marginalia (like the VFR routings through LA Class B) shown below. Hopefully that will be coming soon.



To store your own PDF document in ForeFlight, simply need to email it as an attachment, open the email using the iPad Mail app, tap on the attachment icon, tap the icon in the right upper corner, tap on Open In ..., and select ForeFlight from the list of available apps.



For operators who want to distribute electronic copies of important company documents, like the latest version of their OpSpec, the ForeFlight documents feature should save a lot of paper, weight and heartache. ForeFlight continues to do a good job of balancing their app's feature set so that it is useful for individual pilots as well as commercial operators. ForeFlight also doesn't seem to be afraid to innovate and at this rate, the competition has a lot of catching-up to do.

Tuesday, March 20, 2012

iPad 3 - Heat and Battery Issues


Just a quick update on two hot topics regarding the iPad 3 (aka the new iPad); heat and battery life.

Hotter not necessarily Better

Engadget has passed on some work done by Tweakers.net. Using an infrared camera, they photographed the iPad 2 and iPad 3 side-by-side. After five minutes of running the GLBenchmark app, the iPad 3 was about 5˚C warmer at 33.6˚C (92.5˚F) than the iPad 2.



Heat is certainly an issue for pilots using an iPad EFB in non-airconditioned cockpits in hot weather, but it's too cool in my neighborhood to provide any empirical data on the iPad 3 just yet. I can say that I've flown with both the iPad 1 and the iPad 2 in some hot weather and I saw my iPad 1 display the "Help me Spock, I'm too hot!" message, but only once. The outside air temperate at the time was over 100˚F. I simply turned the iPad 1 off, moved it to the shade, directed an air vent toward it, and it a minute it was operating again.

I've flown in similar temperatures with the iPad 2 and have never had it overheat, perhaps because I was more conscious of the possibility. The iPad has no internal fan and all the heat is radiated by the outside case, so the techniques I recommend for keeping any iPad from overheating are:

  • Don't run the display continuously
  • If possible, run the display slightly dimmed
  • Turn off 3G or 4G
  • Avoid cases and kneeboards that completely enclose the iPad
  • Avoid dark colored cases and covers
  • Keep the iPad out of direct sunlight
  • Direct an air vent toward the iPad
  • Don't leave your iPad inside a parked car or aircraft

If your iPad does overheat, turn it off and wait.

Battery Life

The iPad 1 and iPad 2 have demonstrated a solid battery life of at least 8 hours under intermittent use, but the iPad 3 with 4G appears to be a different story. It takes more juice to drive that high-density display and the latest 4G hardware. I flew with a pilot last night who purchased an iPad 3 with 4G and we tried an experiment. He started the flight with 97% battery capacity and he left cellular data and LTE turned on. I had 99% capacity on my iPad 3 WiFi.


After 35 minutes, his battery was down to 85% capacity while mine showed about 97%. He turned cellular data and LTE off which leaves the internal GPS on and functioning. After flying for another 45 minutes, his battery showed 78% capacity while mine showed 94%.

I should note that we were approaching dusk, we had both dimmed our displays about halfway through the flight. Another difference was that the 4G iPad's display was running pretty much continuously. My various app display options were set to sleep, so my iPad 3's display was probably on less that 50% of the time.

My recommendation for getting the most out of the iPad's battery (regardless of model):

  • Don't run the display continuously
  • When possible, dim the display
  • Use an external power adapter (charging will undoubtedly generate heat)
  • Use an external battery
  • Turn off LTE and Cellular Data while in flight
In ForeFlight Settings, turn on the option Allow Device to Sleep.

For Jepp MobileFD, go to iPad Settings, select JeppFD, and turn Sleep Mode on.

For SkyChartsPro, go to iPad Settings, select SkyChartsPro, and turn off Display always on.

If you are traveling and plan to use 4G while on the ground, you'd be well advised to carry an AC power adapter and use it.

Cost of Change

These two iPad 3 issues are not necessarily deal-breakers for those wanting to upgrade, but they will need to be managed. What, you thought you'd get razor-sharp graphics and fast wireless data for nothin'?

Sunday, March 18, 2012

New iPad Review

There's the knock at the door, you feel the package in your hands, you unwrap it ... Who doesn't like the excitement of exploring new stuff?

If you've read the reviews to date you probably know the basics: The new iPad is a bit faster than the iPad 2, it has more cache, but it also needs that cache to support the high-density "retina" display. If you choose to get the 4G model (I chose Wifi), there are reports of impressive data bandwidth - 14MB/sec or better in some urban areas. Used judiciously, this could be a very good thing. Use that bandwidth gratuitously and you'll go through your monthly data limit in no time, not to mention your battery.




The new iPad is a bit thicker and heavier than the iPad 2, but to tell the truth I couldn't really notice any difference. If you have a magnetic Smart Cover, it will work just fine with the new iPad. Rear cases for the iPad 2 are incompatible with the new iPad and third-party suppliers are only now beginning to get some offerings out there. On eBay I found an inexpensive, bare-bones transparent case for the new iPad that works with the Smart Cover for a mere $12.99, including shipping. Other third-party cases may be sexier, but they can set you back as much as $60, or more.

Early benchmarks seem to indicate the iPad 2 and the new iPad are essentially the same when it comes to processor and memory performance. I find the new iPad a bit faster when it comes to downloading chart updates and the crispness of the retina display is a noticeable improvement when viewing PDFs and Jeppesen's rendered charts. Try something like scrolling through Google Earth and you'll see a marked difference. In general, most any text that is rendered on the new iPad's retina display looks a lot better.

Storage, WiFi, 4G ...

I previously recommended the 16GB iPad as being sufficient for most pilots. Lately I've had to clean out unused apps and data from my iPad 2 because I was down to 1.8GB of free storage. For the new iPad, I chose 32GB and that seems to be adequate for my needs. Then again I have loaded three EFB apps as well as numerous presentations, spreadsheets, and PFD documents. If you want to store a lot of music or a movies for that long airline flight, you may want to give some thought to more storage or consider an external storage device.

My choice was to continue to with the WiFi model rather than go 4G, mainly for budgetary reasons. Yesterday I flew with a pilot who had just gotten the 4G version. Just before engine start, he realized he hadn't transferred his ForeFlight Checklists. No problem. He was able to sync his check list to his iPad over 4G in what seemed like about 10 seconds. As an aside, ForeFlight Checklist Pro, having been designed for the iPhone and needing to be run in 2X mode, looks fantastic on the new iPad retina display.

The downside of 4G would seem to be battery life. After a 1.5 hour flight, the battery on the new iPad 4G was down to 5% from almost being about half charged at the start of the flight. More investigation needs to be done, but it would appear that disabling 4G or using an auxiliary power source in flight is a must with the new iPad. After two solid days of flying, my new iPad WiFi battery life seems exactly the same as the iPad 2.

Another preliminary observation is that my new iPad may run a bit warmer. Right now the weather is cool in Northern California, so time will tell if the extra graphics and cache will contribute to higher operating temperatures. Right now, I haven't seen any heat-related issues.

Upgrade or Wait?

To buy or not to buy? That is the question for many pilots. If you are an original iPad owner, moving up to the new iPad is a no-brainer. If you currently own an iPad 2, I don't see a pressing reason to upgrade unless you need 4G performance, you have filled up your storage, you have need for the retina display, or you just must have the latest/greatest and you have the requisite disposable income. If you do choose to trade up from the iPad 2, you'll undoubtedly be able to sell it for a higher price now than if you wait until the next product offering.

Rumors abound about a smaller form factor (7.85") iPad being released in October 2012 to compete with the Kindle-sized readers. A smaller iPad could be a viable device for yoke mounting in an aircraft, but we all know about rumors. The reasonable assumption would seem to be that any follow-on to the new iPad (whatever it will be called) won't hit the market for at least another year. The bottom-line for me is that the new iPad WiFi is drop-in replacement for the iPad 2 and performs just a well as its predecessor.

Thursday, March 01, 2012

Odd Winter, Endless Possibilities

It's been a dry winter in Northern California and warmer than I can remember in the three decades I've lived here. There have been a few rain showers, but fewer than these photos might lead you to believe. Instead of getting a bit of a break in December, January and February, I've been flying. A lot. Here are some of the nice sights.