One Ugly Cell

Today was shaping up to be a great day to fly…high overcast and calm winds. Not exactly the type of day you’d think of going out flying. So I was pretty pleased to get an out of the blue demo flight show up. Had him all SFAR’d and through my ground routine, let him work through the pre-flight since he seemed interested. And then as I look up from the start-up checklist I see one ugly cell. Over the next 5 minutes I watch it close in on us, and I decided not to do the flight. Felt bad after dragging that guy through everything to bag it the minute before turning the ignition. Think I made the right choice?

KPWT 262155Z AUTO 20012KT 10SM FEW039 FEW047 BKN055 10/03 A3014 RMK AO1
KPWT 262135Z AUTO 21009G15KT 10SM SCT037 BKN046 BKN055 12/02 A3015 RMK AO1
KPWT 262115Z AUTO 22008KT 180V240 10SM BKN037 BKN048 BKN055 11/03 A3014 RMK AO1
KPWT 262055Z AUTO 17006G14KT 10SM BKN037 12/03 A3015 RMK AO1 57003
KPWT 262035Z AUTO 20003KT 10SM BKN034 BKN043 11/03 A3015 RMK AO1
KPWT 262015Z AUTO 24004KT 10SM FEW025 BKN036 BKN041 11/03 A3016 RMK AO1
KPWT 261955Z AUTO 18004KT 10SM FEW026 BKN035 09/03 A3016 RMK A

True vs Absolute Altitudes

In one of the recent AOPA newsletters I get, there was training tip on remembering the different altitude terms. Indicated, pressure, and density altitude are all pretty easy to remember–and, since you use them all the time, they’re also easy to understand and apply, right? Density altitude is what you use on your performance charts, and it takes into consideration 2 things: pressure altitude at the landing site and temperature. Not an elegant definition, but a working one. Pressure altitude is corrected for…atmospheric pressure, or is what the altimeter shows when set to standard pressure. And indicated is…wait for it, wait for it: what you see on the altimeter.

The 2 that trip me up, especially on tests, are true and absolute. The best excuse I can come up with for this is that you just don’t use those specific terms day-to-day, even though you constantly apply the concepts of both true and absolute altitudes. What we (or maybe just “I”?) need is a memory aid to help us when somebody asks for true or absolute altitude, or we see those specific terms in our studies. I got all excited when I read that newsletter:

Memory aids may help you remember the meanings. Indicated altitude is just that—the altimeter’s indication at the current altimeter setting. Pressure altitude is what you get when you set standard pressure (29.92 inches hg) on your altimeter. Density altitude is an important calculation telling how air density at any level is affected by nonstandard temperature and pressure. True altitude is defined as the “vertical distance above sea level.” Think of it as the true yardstick measure. Absolute altitude is the vertical distance of an aircraft above ground level, and is an exception to the above rule that altitudes are usually referenced to sea level.

Well, those are a little helpful, but a memory aid should be something that really sticks with you. For example, during grad school, I walked into class one day, and the last lesson from the class before was still scrawled on the chalkboard: “Some Say Marry Money But My Brother Says Big Breasts Matter More.” Can’t tell you what my class was about, but never forgot that.* CAMAFOOTS, IP-TA-FER, 7-5/taken alive! are some of the ones I like for required equipment, position reporting, and squawk codes. Here’s what I came up with for Absolute and for True:

Absolute = Altitude Above ground, or just remember that the A in Absolute is for the A in AGL

True = altitude in the Troposphere

Not elegant either, but maybe they’ll provide a some simple terms that help you form a mental image of these two terms.

*(it was the med students trying to remember the order of sensory and motor neurons)

Winds Aloft When You're Never That Aloft

The Winds Aloft Forecast (FD) is a prediction of wind direction, wind speed, and temperature at altitudes from 3000 MSL to FL390. I’m adding an FD Helicopters Mini-Lesson on this weather product, but it basically focuses on what we might be using the FD for.

Maybe you don’t even look at this report (or the wind streamlines chart) during your pre-flight planning, and only venture to decipher it prior to check rides. For helicopter pilots, the goofy rules that kick in closer to the stratosphere than we’re ever going to be (like wind speeds >99 knots, and the different nomenclature for below-zero temps at altitudes above FL240) make the FD seem more like fodder for trick questions than a practical tool. I’ve always considered it simply as a back-up source for figuring my en-route winds on cross-country flights, but here’s something cool that the FD table can tell you. Check out this FD from over Nantucket (ACK) for today, and specifically look at the 12000 and 18000 columns:

FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
ACK 3310 3414-05 3212-11 2812-17 2845-28 2863-39 286552 295352 293752

Well, it’s not a brilliant example (but it’s the best I could do today), but between 12000 and 18000, the wind speed is forecast to increase from 12 to 45 knots, or 5.5 knots per 1000 feet. As a rule of thumb, when wind speed increases by >6 knots per 1000 feet, you can expect moderate or greater turbulence.* I’m not going to call it definitive–and keep in mind that the FD is just a forecast–but at the time there were a couple of PIREPs for light to moderate turbulence in the KBOS area.

This came up for me before my commercial cross-country flight. I was looking forward to flying into a mountain airport (KMYL) and the weather was pretty much a go as far as I was concerned. Winds were dead calm at KMYL, and the sky was clear below 12000, as it usually is in the Boise Valley. The one thing bothering me was an AIRMET Tango overlying KMYL. It didn’t go down to the surface, but it did get close enough to the altitude we’d be flying to get into this airport that it had me thinking over whether it was going to be safe to make the flight. I remember being a bit baffled by the calm winds at KMYL and the high winds at the 9000 foot level for the KLWS FD. I talked it over with the CP and, even though he didn’t tell me outright not to make the flight, I didn’t get the feeling that he’d do it. So I bailed on that cross-country, and ended up second-guessed that decision extensively—I’d just cost the school’s owner a 4-hour block on that helicopter, and another student was walking out to do that exact same flight solo (until her instructor called her back after I decided not to go on my flight). It wasn’t until months later that it hit me: that AIRMET Tango was probably there because of the turbulence between the dead calm layer near the surface and an overlying windy layer, and that’s probably about the altitude I’d have been flying at to get over the ridgeline and into KMYL.

So even though the FD might not look especially relevant for a flight at 1000 AGL, you can still use it to guess when and where you might encounter turbulence. In the absence of better info (like a PIREP with wind or turbulence reported), a difference in wind speed at the surface reported on a METAR and forecast winds at the lowest altitude from the FD could be a warning sign. For example, if the winds forecast for KXYZ (elev 18 MSL) on the FD was:

FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
XYZ 3129 3133-01 3138-04 3044-08 3045-17 2845-28 286042 275952 275460

and the METAR was reporting:

KXYZ 132256Z 20006KT 10SM SCT160 15/07 A3005

You might want to consider the possibility of a bumpy ride.

*I’ve seen this in a few places, but the closest that I could get to for a credible source is an old Navy manual, the Aerographer’s Mate 14010. Unfortunately, it’s not in AC 00-45F (Aviation Weather Services), AC 00-6A (Aviation Weather), or the AIM. It was also the topic of a question in AOPA Pilot (Nov 2009).

The 60:1 Rule

No I’m not talking about the number of students who go through helicopter flight school for every instructor that gets hired. Actually, there are several problems on the Commercial Helicopter Pilot Knowledge Test that require you to understand this rule. In short, the 60:1 rule refers to the relationship between distance from a VOR or ADF station and the ground distance of 1 radial. At 60 NM from a station, if you cross 1 radial you will have covered 1 NM of ground. There are some things you need to do, like maintaining a constant heading, knowing your true airspeed, and timing how long it takes for you to cross the radials, but that’s the premise of this problem.

When I went through my commercial ticket, this was a stumbling block for me, and it took me a while to figure it out. I’m not mathematically inclined–1 of the 3 C’s I got in college was in calculus II, and the only thing I remember from that class was that the instructor wore the exact same sweater to class every single day. Yep, true story. Anyway, a friend recently asked me to endorse him for his CPL(H) knowledge test. Before I offered him an endorsement, I asked him to do several knowledge tests and he also hit a wall with these questions. Smart guy too–went to grad school, has his A&P, Inspector Authorization, and rebuilds helicopters for fun. Fact is, the 60:1 rule questions aren’t hard–they are very easy. Why is it that they cause trouble?

Like anything else, you and I can only teach what we’ve been taught, and the 60:1 rule isn’t taught well in any of the helicopter textbooks or the Jeppesen Commercial/Instrument Handbook (which I think is a waste of 0.3 flight hours’ cash). Since you only need it to pass the Commercial and CFI written exams, why not just memorize the answers and move on?

Yeah, you could do that. But I’m guessing that the instructors and students who read this blog are setting a higher standard for themselves. I was disappointed when my instructors glossed over questions or didn’t know things that I knew. Like you, my mission is to raise the bar a little so the next generation of students is a little better trained than I was. So here’s my lesson plan for teaching the 60:1 rule, along with a short animated graphic to help out those of you who like to see concepts illustrated. The animation takes about 30 seconds to run, and I’ll admit that it’s not going to dazzle anybody, but it does more to explain the application of the 60:1 rule than the spiffy graphics in the Jeppesen book does. Now you can impress your students, other instructors, and your friends with your command of this archaic piece of trivia!

Tim's VOR Simulator

It’s pretty much the Pong of flight simulators, but this little tool can seriously save you on ground school and flight training. I’ve seen friends struggle with VOR navigation, especially when studying for the PPL and CPL written exams, since most of the helicopters we fly aren’t equipped with an VOR or HSI. Worse, an ADF in a helicopter is as common as an AM radio in a new car, and I’ve never seen an RMI outside of a textbook. Yet these are worth more than a few points on every written you’ll take.

Even in instrument trainers, these traditional navigation systems–even if they’re in there–often get passed over for the ubiquitous GPS. It’s just as well. Everything you need to know about navigating by VOR/HSI/ADF/RMI can be done efficiently and cheaply at your computer. You can forgo thousands of dollars trying to do the mental work that interpreting these instruments requires while continuing to fly an aircraft in the real-world (with turbulence, imperfect/absent lesson plans, ATC and radio chatter, etc.). You just have to have the right tools.

When you start your instrument training, you’ll be tempted by Microsoft Flight Simulator. For the cost of 15 minutes in the school’s R44 instrument trainer or a half hour in their Frasca, you can get MSFS X and a joystick. Then it won’t run smoothly on your computer, and you won’t be able to fly the Jet Ranger (but you’ll spend a few hours trying). Then you start thinking about a better machine and rudder pedals, get bored and frustrated, then take a few turns in the Extra 300. 3 hours later you’ve accomplished nothing. Save yourself. MSFS has it’s place for practicing instrument skills, but not in the Jet Ranger, and not from pick-up to set-down, but that’ll be the topic of another post.

Tim’s VOR Simulator, in contrast, is free, runs pretty well, is easy to find online, and you just have to know a few keyboard commands to fly it. It has all the functionality you need to practice simple problems (where am I relative to the VOR?), and can help you isolate the skills you’ll need to fly complex holds and approaches. Best of all, it’s free to anybody with a computer and internet connection, saving expensive cockpit time for consolidating the motor skills that can’t be replicated well even in the best simulators. Tim’s VOR Simulator allows you to set your speed and heading/turn rate with simple keyboard commands. Master that and the program’s quirks, and you can sit at your desk, at school, or in a coffee shop and focus on the mental part of instrument flying (and instrument flying is all mental). Make a mistake, and you can stop the simulation immediately and start over. Altitude isn’t a variable (which further improves the value of this tool for isolating specific skills), but wind can be introduced to teach wind angle corrections.

When you can fly this procedure with Tim's VOR Simulator, young Grasshopper, then you will be ready to fly by instruments.

Most people don’t know about this option though. My instructors didn’t (and they weren’t interested when I showed them). And every few months somebody will get on the forums asking about the best simulator for learning instrument procedures. So I’ve added a Tim’s VOR Simulator Lesson. It’s not a VOR navigation lesson, but just a lesson on how to use Tim’s VOR simulator to learn radio navigation. It’s also not an instrument lesson. This lesson is intended for student pilots working through their ground school and studying for their FAA written tests. The problems are remedial, but if you don’t understand radio navigation, you’ll struggle with them. I’ve also put some simple videos on YouTube that demonstrates these problems (sorry, no audio for them…I’ve had  a sore throat for the last couple of days).

Once you know how to work the simulator, you’ll see how you can easily use it to learn instrument skills (when you’re ready). But in the beginning, its simple interface can actually be a pain in the ass if you aren’t committed to trying it out. This lesson plan demonstrates some simple exercises you can do with the simulator that will open this tool up to you. Once you get past how to set up problems, the biggest barrier to continuing to use it is boredom. But that’s actually what you’re trying to accomplish. When navigating by VOR is as mundane as following a highway, or you can fly some wacky procedure while drinking a beer at 01:30 while seeing what the JustHelicopter trolls are up to in another window, then you won’t be making expensive mistakes in the air.

Really, ADF/RMI navigation, approaches, and holds are so much easier when you can see the instruments react in real-time and test your understanding. While drinking beer. I’ll do more of those video lessons or design some more structured problems, but it’d help if I got some feedback about what types of problems students are having trouble with.

Dynamic Rollover

In theory, we all know what to do to prevent dynamic rollover. This has been a frequent cause of training accidents, so the FAA has made it a focus area. And those of us who’ve been to the Robinson course remember the rooftop landing video where the pilot could have saved himself by simply lowering the collective after a hard landing. In the Dynamic Rollover lesson plan, I’ve included 2 videos: the first is of a Rotorway pilot who sets down hard and catches a skid on some uneven concrete. It happens fast, but right before the dynamic rollover happens, you get a good look at just how much of an angle the helicopter can take before reaching the point of no return. In the second video, you see that this isn’t just a problem for low-time pilots. This video shows the Red Bull AH-1 Cobra picking up from a turf field. It looks like the heel of the skid digs into the turf and becomes the pivot point, both for bank and roll. They’re pretty close to losing this helicopter, but the skid pulls free. Clearly some high-time pilots flying that ship, but they also failed to react the way we’ve been told to in training.

Part of the issue–and this probably applies to all emergencies–is that we’ve taken off hundreds of times without a problem. Back about 12 years ago, I took this trip to Scotland. I’d been touring up north, as far as Loch Ness, and was heading back to my room on the Kintyre Peninsula. I pushed my rental car’s fuel to it’s limit–partly because I was doing the trip on a budget, partly because there just weren’t that many gas stations. So it’s Sunday night, but still light and I didn’t notice how late it was getting. I knew I needed gas, but every gas station in every little town I passed through was already closed. The last town was 15 or so miles from where I was staying, and I made a calculated risk: I could spend the night in the parking lot or I’d have a shot at sleeping in my bed. Based on what I knew about the fuel remaining when the light had come on, I figured I had a shot at making it, so off I went. I grew up in Central Texas, but this place redefined rural. Right at about the halfway point, there was this little hill, and halfway up, the car just died. This shouldn’t have been unexpected, but my initial reaction was that something else was wrong. I was convinced that I had the fuel to make it, and I’d never run a car dry, so I had no idea of exactly what to expect. I instinctively just pushed the clutch in and turned the key, and there was a few seconds there where I just didn’t register what was happening. I believed that this stretch of the drive would be the same as every other time I’d set out in the car, and when it didn’t turn out that way, I needed time to process why. I ended up sleeping in the car, surrounded by flocks of sheep, and hitching a ride into town the next morning with some shepherds.

I think the same happens to us as pilots. We come to expect that the pick-up or landing is going to go the same as it’s gone the last hundred times that we’ve done it. When it starts to go bad, you just keep doing what you’re doing, until you’re rolled over or you process what’s happening. I also learned this during my training. In the summertime, the tarmac heats up enough that the skids sink down into it. In fact, you can see impressions from the skid plates all over the ramp. Once, one of the skids stuck enough that we felt just a slight roll, and an instant later the skid broke free. We popped right up into the air and wobbled there for a second. That time I knew what happened, but it went so quick that neither my instructor nor I had the chance to react. Since then, part of my preflight has been taking notice of what surface the skids are sitting on, and whether they might stick on the pick-up. Before starting up, I also started verbalizing this to my instructor (although a better practice would be to verbalize it right before picking up, since your short-term memory isn’t likely to hold this bit of info that long).

If you do decide to check out the lesson, take a second to at least rate it. Always useful information for me and for others who come after you.

North Pacific Hurricanes

The North Pacific is a source for some pretty impressive low pressure systems. Stick them in the GOM, and they’d look like hurricanes. The one that blew in thisOR-Winds week had a pressure below 1000 mb and winds in the 40-60 knot range, which rivals a category 1 hurricane. The difference, I suppose, is that the warm waters of the GOM produce convective activity that strengthens the low, but this source of energy is missing in the higher latitudes of the Pacific. This storm caused some problems on the coast, but the winds dissipated pretty quickly.

What I wanted to point out about this particular system was the correlation between the pressure gradients and the winds. In this overlay of the SFC Prognostic Chart and the Wind Streamlines, you can see the low in the upper left corner, off the Washington coastline. Just southeast of the low the isobars are stacked pretty close together, but spread out as you move south along the coastline. The wind streamlines reflect the effect this has on wind speeds: southeast of the low, right where the isobars are stacked, the winds peak at hurricane force. North and south of the low, the winds meander around and peter out as the pressure gradient–the distance between the isobars–dissipates.

Do you know what the hatched area that stretches from central Mexico, through Utah and all the way up the west coast on the Wind Streamlines graphic is? Here’s a hint: the wind streamlines image I used was for the 3000 MSL level.

Mystery Solved

Turns out it wasn’t a fog blanketing the area…we were getting dust dropped on us from a dust storm to the north. The MODIS satellite imagery from yesterday shows the dust getting kicked up and blown to the southwest. And walking through the yard today I could see a puff of dust kick up with every step. Yes, I often ask myself why I moved here from Seattle.


I went back and scanned the METAR data for yesterday. An hour after I posted, KPSC started reporting haze (HZ), which pretty accurately describes what the skies looked like by mid-afternoon…

METAR KPSC 041653Z 01019G23KT 7SM HZ FEW100 14/01 A2977 RMK AO2 SLP081 T01390011

And later in the day there were a few METARS that coded it for what it was…

METAR KPSC 050253Z 01016KT 5SM BLDU CLR 14/M01 A2981 RMK AO2 SLP096 T01391006 53018

One clue should have been the temp-dew point spread, which never got close enough for fog formation.

The storm got awful enough that they shut down sections of I90 to the north of us. Oddly enough, from the METAR data you’d have never seen it…there wasn’t a weather station within the storm, and the AIRMETs for that morning only showed a Tango over eastern Washington.

'Morning Sunshine

I couldn’t see across the river this morning. Typical winter weather in the Columbia River Basin…cold air, moisture, and the bowl shape that we live in is conducive to fog and clouds getting in here and staying for days. From home I can look at the web cam at KRLD, which is 11 o’clock and a couple of miles from home. They don’t have a ASOS, but KPSC (8 miles to the east and a bit further from the river) is reporting:

KPSC 041453Z 01017G22KT 10SM BKN080 12/01 A2974

krld rwaywindsockbridge

Clearly the KPSC picture is a little different, and the picture on the far right shows the WA DOT traffic cam that is a little closer to that airport. It does show the winds are about what I thought, 15-20 knots. Dewpoint is off–maybe the river is adding the additional cooling and/or moisture that’s keeping the fog on the ground at KRLD. What I still find interesting is the combination of heavy fog and wind–this isn’t what the textbooks tell you is supposed to happen. The windsock at KRLD is standing straight out, and a 15-20 knot wind is supposed to pick that fog up and make it a low stratus layer. But I can’t see 1500 meters across the river, and the visibility at KRLD sucks.

If you’re still reading expecting me to give you an answer, sorry to disappoint. But I can throw in some other confounding observations. On the visible satellite (below, left) you can see the clouds filling the Basin as the sun comes up. From the east. Usually moisture comes into this region from the Pacific Ocean to the west. Low pressure to the southeast is the reason for the easterly winds, and I can only assume that the moisture was brought in here with the front. The other unusual thing is that the Cascade Mountains also form a barrier to low clouds, and if it’s a clear day here and IMC in Seattle, you can often see a north-south line of clouds formed by the terrain holding them to the west. That’s not what’s going on today though. On the IR satellite (right side), the clouds overhead are relatively bright. If I remember correctly, bright clouds on IR indicate colder, high clouds. Fog is low and warm, and doesn’t always stand out on IR. There must be a higher cloud layer obscuring the low fog layer around us.

The take-home from this, for the low-time pilot with little knowledge of real-world weather and a limited understanding of the local weather patterns, is that I might not be a happy camper if I’d planned on scooting over to KRLD this a.m. I’d have launched that way expecting gusty winds based on the KPSC ASOS, but with the winds and 8000 CIG/10 sm VIS reported, I wouldn’t have expected to find IMC (or, at best, MVFR) at KRLD. PIREPS wouldn’t have helped me (none are reporting sky conditions), and the few airports in this region are reporting VFR. If I was coming from the west, I’d have been faced with the decision to press on to KPSC and try to land there, or turn around and head back into the desert. In this case, having that WDOT weather cam at KRLD would have made a huge difference in deciding whether to make the flight or not. I wouldn’t have thought to include a weather cam in my pre-flight planning.