Thursday, August 28, 2014

RNAV OBScurities


A few years back the editors of the Aeronautical Information Manual changed the well-written overview of GPS, which was a shame because that concise description laid the conceptual framework pilots needed to understand waypoint sequencing, turn anticipation, and how and when to suspend waypoint sequencing. For their part, instructors are so busy teaching pilots how to wrestle with crappy GPS receiver user interfaces that a conceptual understanding of GPS often falls by the wayside. Many pilots have memorized the series of button pushes and knob twists that will accomplish their goal, but fewer actually understand the goal. Even if you consider yourself a GPS black belt, there are advantages to acquiring a deeper appreciation of three key GPS concepts:

  • Waypoint-based navigation
  • Automatic waypoint sequencing
  • Turn anticipation (illustrated above)

Direct-To Limitations

Most pilots grasp how to use the GPS Direct-To button and some pilots never move beyond that feature because Direct-To is simple: Input one waypoint, dial in the desired track on the Omni-Bearing Selector (OBS) or if you're lazy, just find a heading that keeps you on magenta line on the moving map. If your aircraft has an electronic HSI, it will set the desired track for you - Even better! Heck, you might not have to interact with the GPS for the rest of the flight. Yet simple answers to complex problems can themselves be problematic.

Indiscriminately flying Direct-To can take you to all sorts of places you don't want to go, such as into restricted/prohibited airspace, weather your aircraft is incapable of handing, or obstacles and rising terrain, as shown below.



Finding your Legs

Entering a sequence of waypoints is time-consuming and can be frustrating, but once you learn how to create a flight plan you'll find there are lots of advantages. You can create a sequence of waypoints that keeps you clear of the aforementioned bad stuff and you'll be the beneficiary of two GPS design features that many pilots take for granted: Turn anticipation and automatic waypoint sequencing. Simply put, as you approach the current waypoint, the GPS will anticipate the turn, tell you when to turn, and then automatically sequence to the next waypoint. If you don't have an electronic HSI, you'll have some work to do - set the course pointer (or Omni-Bearing Selector) to the new desired track. Many pilots skip this step, and that's a shame.

As you start creating flight plans, you introduce another concept that you'll need to understand: Leg-based navigation. A leg is simply the straight line between your last waypoint and the current waypoint. If you wander off the current leg, or are vectored off by ATC, you may need to re-intercept the leg or intercept the next leg in your flight plan. This is where many pilots jump to their old standby - Direct-To - and don't fully understand the desired goal of activating, and then intercepting, a leg rather than proceeding direct to a waypoint.

Let's say you're departing Franklin Field and have entered this flight plan.



By default, the active leg is from Franklin (F72) to the Sacramento VOR.




Let's say you actually want to fly a 250 heading and intercept V334, the leg between SAC and VISTO. Proceeding direct VISTO is not the answer. Instead, select VISTO and you'll have the option of activating the leg between SAC and VISTO.




Note that when you activate a leg on the G1000, the SUSP soft key will appear on the PFD. Many pilots see that SUSP key and mistakenly think something isn't right or that they need to press the SUSP key. Don't worry, everything is fine. It is normal for SUSP to appear when a leg has been activated, but not yet intercepted. And no, you don't need to do anything - just continue flying, intercept the selected leg, and the SUSP key will disappear.

OBS: When and Why

Another concept to understand when you use flight plans is how to select your own desired track to the current waypoint and suspend waypoint sequencing. A few examples:
  • You are flying under instrument flight rules and instructed to hold over the Current Waypoint
  • You want to select your own desired track to the current waypoint to avoid terrain
The first question is "Why is that button called OBS?" The name seems to have an OBScure history. You dial in a VOR radial using the Omni-Bearing Selector (or OBS) so some engineer (or committee of engineers) got the bright idea that the function that allows you to select your own desired track to the current GPS waypoint should be called OBS. Whatever the genesis of this convention, the important thing to remember is that the OBS function does two things:

  1. Lets you select your own desired track to the current waypoint
  2. Suspends waypoint sequencing
Traffic Pattern Entry

Many newer GPS receiver (and iPad apps) let you display extended runway center lines at an airport to help you visualize your entry into traffic pattern. You can do the same thing with your GPS by pressing OBS and dialing in the magnetic course of the runway as the desired track. Let's say your inbound to Lampson-Lakeport from the northwest.



Note that this example uses the Garmin GTN Trainer for the iPad which requires you to input the desired track when you press OBS since there's no Course Deviation Indicator (CDI) or Horizontal Situation Indicator (HSI).  Select the desired track for runway 28 (your desired runway at 1O2).


After selecting 280˚ as the desired track, you now have a magenta line on the GPS moving map that depicts the approximate final approach to runway 28. Remember that the waypoint for an airport is usually the surveyed center of the airport so this magenta line approximates the final approach course. Despite the funny name, OBS can be useful for situational awareness and planning your traffic pattern entry.



OBStacle Departure Procedures

Let's say you have an IFR clearance to depart runway 31 from the San Andreas/Calaveras Airport via the published Obstacle Departure Procedure (ODP). The raison d'ĂȘtre for ODPs is to provide a description of one or more routes that will keep you from running into terrain or obstacles while departing an airport under instrument flight rules (IFR).


Since most GPS-equipped aircraft also have VOR receivers, you could just use tune the LIN VOR and use that to intercept the desired radial, but wouldn't it be nice to have the moving map on your GPS match the ODP game plan? The first waypoint in your flight plan is LIN and your GPS defaults to a direct leg between the airport (KCPU) and the LIN VOR. This is not the route described by the ODP and for good reason: It takes you right toward rapidly rising terrain. Duh?!



So press OBS and dial in the 029˚ radial FROM LIN (029˚ + 180˚ = 209˚ TO LIN).



You've successfully set the desired track to LIN, but the course after LIN no longer follows V113: It is just a white straight line directly opposite the desired track you just set, indicating that waypoint sequencing has been suspended. If you forget to press OBS again before reaching LIN, the GPS won't sequence to the next waypoint in the flight plan. Bummer!



With newer Garmin GPS receivers, you can press OBS a second time and this will not only retain the desired track that you selected to LIN, it will reenable waypoint sequencing, too. Awesome!


Asking yourself "Why?"

So that's a brief description of the GPS concepts of waypoint-based navigation, automatic waypoint sequencing, and turn anticipation. Now it's up to you to decide if you want to be one of those pilots that always uses Direct-To, or just memorizes button pushes and knob twists, or if you want to actually understand the underlying concepts.

Saturday, August 23, 2014

ForeFlight adds Weight & Balance


A few weeks ago, I had a discussion about flying an aircraft over gross weight and the person I was talking to seemed to be saying "It ain't no thang ..." I begged to differ since there are serious hazards associated with flying an aircraft over maximum takeoff weight or out of the CG envelope. And so I was pleased to see the addition of Weight and Balance calculations to ForeFlight, though one has wonder just how many more features can be added to ForeFlight as it continues to mature. So far the developers have done a decent job of adding features in a logical fashion, but there is a tipping point for software products, a point where efforts to increase/maintain sales or market share and generate income required to support a growing company can eclipse good design philosophy and ease-of-use. Draw your own conclusions about how robust the feature count can become before a product begins to become less usable: That's another topic, perhaps for another day. The task at hand is to review ForeFlight's new weight and balance feature.

I've always felt that a good (perhaps the best) way to evaluate user friendliness is to dive in, start using the product, and see how far you get. Tapping on "More ..." led me to the new weight and balance feature. So far, so good.



Entering the registration number for a DA42NG I fly regularly, I encountered my first snag: Seems that ForeFlight uses the FAA's database to look up the aircraft type in an attempt to automatically configure the stations and arms. Unfortunately, ForeFlight was confused by the serial number it retrieved for the DA42NG registration number I entered. The assertion that the serial number for a DA42 NG should begin with "42.N" or "42.NC" is, as the British say, "A bit silly." You see, many DA42 TwinStar owners who had trouble with the notoriously unreliable 1.7 engines took advantage of an offer Diamond made: Since Thielert hadn't yet emerged from bankruptcy, these owners took their aircraft back to the factory and had them converted to a DA42NG. The aircraft kept the same serial number, but they were no longer a "TwinStar" and even the badging on the aircraft was changed to "DA42NG."

Not understanding the intricacies of DA42 serial numbers, ForeFlight's valiant attempt to be super user friendly took a wrong turn: I now had to enter pretty much everything: Arm for each seat, baggage area, fuel tank, deice reservoir, and so on. Being a loyal ForeFlight user and what some might call "hard-headed," I persevered.



That's when I realized there was an error of some sort because the CG was out of range. An email to ForeFlight support received an extremely quick reply with the solution: Since all the other fields I needed to define required a station (or arm), I hadn't noticed that FF requires you enter the aircraft's empty weight and moment, not the CG. Shouldn't it let you choose whether you want to enter the empty CG or moment? In fact, in other areas, the app offers just this sort of flexibility: Fuel tank loadings allow you to enter pounds or gallons and ForeFlight will calculate the field you didn't enter. Personally, I'd rather enter a 4-digit number for empty CG rather than enter a 7-digit number for empty moment. Tisk, tisk ...



Most common aircraft types will be automatically configured without fuss. By the way, if you see an option for configuring Normal or Utility category, you best choose the Normal category because ForeFlight doesn't seem to be able to simultaneously display both envelopes for aircraft that have been certificated in both categories. A nice feature is that ForeFlight will notify you when it has made choices for station distances for things like seats that move so that you can adjust them to your liking.



The Setup feature also allows you to name and define frequently carried items, such as your SkyOx system that weighs 6 pounds, but you have to associate it with a particular location, such as AFT SEATS. When you use the Load feature, simply tap next to the item to include it or remove it from your planned flight. It would be nice if frequently used items could be defined and then dragged and dropped into different locations. That way you could see changes in the CG by relocating Uncle Bob to the back seat whenever Aunt Alice is coming along for a ride.



I don't know if there is an exhaustive list of the aircraft types that ForeFlight can automatically configure, but this is an ambitious design choice. Based on trial and error, here are a few types that seem to be supported for automatic configuration:

  • BE76
  • C172
  • C182
  • DA40
  • DA42 (sorta)
  • M20
  • P28A
  • P28R
  • SR20
  • SR22



A few unsupported types requiring manual configuration that I randomly discovered include:

  • C152
  • C206
  • C208
  • GA7
  • PA34
  • PA46
  • PA44
  • PC12
  • TOBA


If you own an aircraft or rent just two or three aircraft, the overhead of defining your aircraft's weight and balance could be very low or it could be a headache. If you're an instructor or a pilot who flies a bunch of different aircraft, you might find this a bit frustrating. Pressed for time, a frustrated pilot might be tempted to rely on Kentucky windage instead of doing the actual calculations.

There are other weight and balance solutions out there, such as Excel or Numbers spreadsheets. Apps like Gyronimo and Cirrus Perform are easier to use because they are designed for specific aircraft types and they do performance calculations, too. Oh, geez! I mentioned performance calculations. Now I hope the fine folks at ForeFlight don't try to add that feature because being everything to every pilot just isn't practical, nor is it user-friendly.

As St. Francis of Assisi said, "Do few things, but do them well ..."

Wednesday, August 13, 2014

Up the Down Staircase

"Mooselips Approach, Cessna 12345, 3000 feet, request practice ILS 30 at Bison, published missed, information tango."

"Cessna 12345, Mooselips Approach, Bison altimeter 3002, unable ILS 30, runway 12 in use at Bison, did you have another approach request?" 

If you haven't yet had an exchange like the one, it's likely that you soon will because the FAA has decided that opposite direction approaches into towered airports are no longer allowed. To the uninitiated, practice approaches to a runway when there's opposite direction traffic may seem inherently dangerous, but it is something that's been done safely at many airports for as long as anyone can remember. One example in Northern California is Sacramento Executive where all the instrument approaches are to runway 2 and 90% of the time runway 20 is in use.

At KSAC, the procedure for handling opposite direction approaches is simple and has worked well (and without incident, to my knowledge): The tower instructs the aircraft inbound on the approach to start their missed approach (usually a climbing left turn) prior to the runway threshold and any traffic departing the opposite direct turns in the other direction.

For areas like the California Central Coast, the restriction on opposite direction instrument approaches has been in place since I arrived in June and it has serious implications for instrument flight training since the ILS approaches for San Luis Obispo, Santa Maria, and Santa Barbara are likely to be opposite direction 90% of the time. For a student to train to fly an ILS in a real aircraft, you need to fly quite a distance. Same goes for instrument rating practical tests that require an ILS because the aircraft is not equipped with WAAS GPS and/or there's no RNAV approach available with LPV minima to a DA of 250 feet or lower.

There currently is no formal FAA Order (to my knowledge) that describes this restriction, though one hopes that will change: Everyone from students to instructors to controllers would like to see this rule codified. As it stands, this restriction seems to have been passed down from on high to TRACONs in the US. Some exceptions may be allowed when there's an "operational need" such as for FAA flight checks of instrument procedures. You may be able to call your local TRACON on the phone and make prior arrangements if you need to do an ILS for an instrument rating check ride or for practice. And waivers may be issued for some airports with a high volume of training. Then again, your request might still be refused. Your tax dollars at work.