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)

Only 1 Kind of Hypoxia I Care About…

One thing all teachers have to face at one point or another is a student asking “Who cares? Why do we have to know that?” I was recently faced with that question while working with a helicopter pilot who’s sitting for his commercial ride. First some background on this pilot: he’s good. His level of confidence and skill going into his commercial ride well exceeds mine at any time during my training. He has a few things in his favor: he owns and maintains the helicopter, flies it weekly, and has over 300 hrs in it. He’s also been flying airplanes for many years, and knows more about aviation than I may ever know. Most of his flying has also been outside of flight schools. It’s awkward for somebody with as little aviation experience as myself to be “teaching” somebody at this skill level, and if anybody’s learning, it’s me.

His weak point is his book knowledge, and most of my time has been spend going over the PTS knowledge topics with him. After our last meeting, I gave him a list of topics that we needed to cover before I could feel good about signing him off, and I thought I’d heard him say he’d been studying. So I thought I’d put him to the test, hoping I could sign him off for the practical. I started with a topic we’ve all learned at the rote level: “What are the 4 types of hypoxia?”

“There are 4 types? Only one type I care about…the type where you ain’t getting enough oxygen!”

In the ensuing uncomfortable minutes, I fell into a trap that so many other teachers have. Since I couldn’t tell him outright why he should care that there are more than one type, the motivation I provided is that this is something you just have to know for the test. If he’d said “This is stupid!” or “This crap is just relevant for plank drivers” I’d have probably agreed with him as well. And what message would this have sent?

I’m going to try and atone for that now, and I’m going to try and do it with a couple of scenarios that hit the highlights. If you don’t remember, here’s the lesson plan for hypoxia. As part of a lesson on “The 4 Types of Hypoxia” these would be pretty obvious, but as part of a general lesson that included ADM scenarios, you might be able to get a student thinking beyond the rote level.

You’ve been contacted by a rancher who needs to clear some feral goats off his property. He lives in Lakeview (KLKV), and his ranch is to the east (N42 4′ 30″ W120 8′ 20″); you’ll be working mostly to the south and west in some foothills. He’s retired military and a former cop, so he wants to do the shooting. Assume you’re qualified to do the flight and you have access to a helicopter that can perform this mission safely. The rancher offers to put you up Friday night so you can get an early start Saturday morning.hypoxia lesson plan

You arrive the afternoon before the flight and discuss the flight with the rancher over dinner. It sounds like he’s familiar working around helicopters and doing aerial predator control. After dinner he pours you a scotch and, when you decline it, says something about not letting good whiskey go to waste as he drinks it quickly. He has a few more drinks and puffs on a cigar as you chat into the evening. By the time you head off to bed, he’s slurring his speech slightly.

The next morning he’s up and puffing another cigar while you have breakfast. As you review the plan for the day, you notice the bottle of scotch and figure that he probably had 1 or 2 more drinks after you went to bed. He doesn’t seem to be hung over this morning. As he shoulders his rifle, he asks “We ready?” Can you legally and safely do this flight?

Three things come together in this case: the elevations where you’ll be working are generally above 6,000 MSL. Although this is lower than where most people would be be feeling the effects of hypoxia, at those altitudes there is less oxygen available to breathe (hypoxic hypoxia). On top of that, smoking definitely affects a person’s ability to utilize oxygen (hypemic hypoxia), and so can alcohol (histotoxic). Although this rancher might not be visibly impaired, could residual alcohol in his system further sensitize him to the affects of altitude? In this type of operation–where judgment, reaction time, and a good aim are necessary–is this client prepared to conduct this flight safely and efficiently?

You have a commercial student who’s check ride is scheduled for next week. He’s ready for it, but bad weather has kept him from getting his night solo flights done. It looks like the weather tonight, and maybe tomorrow night, will be above the school’s minimums for night solo flights. As you’re reviewing the student’s pre-flight planning and he’s briefing you on his plan for the flight, you notice he has a bruise and needle mark on his left arm. You make a joke about him getting his heroin habit under control, and he tells you there was a blood drive yesterday at work. The weather turns out to be better than expected, and the student appears to be well-prepared for the flight. Any concerns about sending this student out to wrap up his required night solo flight hours?

The issue here is that night vision can be affected at altitudes as low as 5,000 MSL, and supplemental oxygen has been recommended for night flights at or above 6,000 MSL (although this is not in the current PHAK). In this student’s case, a blood donation can cause a hypemic hypoxia condition that lasts for several weeks. If he’s flying out of a high altitude airport, his night vision could very well be affected by the combination of altitude and anemia.

I think these 2 scenarios are both reasonable and realistic, and can be used to teach students the effects and types of hypoxia closer to the application-correlation level. Are they putting unreasonable expectations on the pilot? Like the SCUBA lesson, these topics are here so that you can evaluate your own fitness for flight, and possibly recognize conditions in your clients and passengers that could affect their comfort or health.

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).

Two New Lessons

What I wanted to get across with these 2 lessons isn’t the content of them, but where they fit in a helicopter flight training syllabus. The first lesson is Helicopter Main Rotor Systems (MRS), and the second is Helicopter Crew Resource Management (CRM). Neither of them are lessons that would get a student excited, and if I told you CRM was all part of Aeronautical Decision Making (ADM), that would probably further dampen your enthusiasm. Main Rotor Systems is the very first thing in the FAA’s Rotorcraft Flight Manual, right there on page 1-1. It comes before helicopter flight controls (page 1-3), helicopter aerodynamics (Ch 2), weight and balance (Ch 7), and even basic helicopter flight maneuvers (Ch 9). CRM is one very long paragraph in Chapter 14, and it starts off with something about the airlines. Seven pages later, you’re reading about some crazy thing called an autogyro.

Just judging from where these 2 topics are in the RFM, which one do you think is more important? Which one are you going to use earlier in your training, and throughout your training? Which one is going to make a bigger impression on you–the one you see when you’re fresh and excited about becoming a helicopter pilot, or the one that you have to get done before your check ride next week?

That’s my point. ADM and CRM are things that should be with you starting with the first few hours you log. These 2 topics, though, are shoved to the back of the RFM (and things like Aeromedical Factors didn’t even make it into the RFM). Of course, you don’t have to learn things in this order, but if you don’t know any better, you’re going to read the RFM from front to back like any other book, right? What about your school? Well, the easy thing for a school to do is to just follow the FAA’s lead, and here’s the result:

helicopter syllabus CRM vs MRS

MRS is the very first lesson, and, along with anti-torque and flight controls, gets a generous 2 hours. ADM is the second to last lesson, and gets 1.5 hrs. Again, what does this tell you?

Operationally, I’ve seen plenty of students and instructors roll their eyes and use diminutive descriptors (“such bullshit“) when referring to ADM-type topics. I’ll also admit that I was one of them. Part of my 1.5 hr ADM lesson was spent joking with my instructor to the point of shortening the DECIDE model to the DIE model (Detect, Identify, Evaluate). The chief pilot and in-house DPE wasn’t amused, but Exhibit A: primacy and Exhibit B: he didn’t do much to impress the value of ADM on me afterward.

That actually came $400 later at the HAI Flying in the Wire and Obstruction Environment course. I signed up for that class not knowing really what would be covered, so I was a bit surprised that about 1/3 of that class was ADM/CRM. The instructor’s approach to CRM wasn’t a historical account of what the airlines did, or a series of acronyms that had no operational significance, or what some desk jockey needed to do to implement a CRM system to please upper management. A lot of it was just talking about how we screw up and miscommunicate, and some simple bullet points to tell you how to get out of that rut. By starting the class with CRM, he made the point that “Hey, CRM is critical to surviving the wire environment!It’s more important than learning where to look for wires, what kind of wires are out there, what weather conditions are more conducive to wire strikes. All the interesting stuff, in summary, is secondary to good operational procedures and crew communication. Is flight training so benign that CRM/ADM is effectively just an appendix to your primary training? (For that matter, if you’re doing off-airport landings, you are in the wire environment.)

I’d been meaning to write up a few lessons on CRM/ADM, and something from the Wire Environment course, but it was a post on VerticalReference that inspired me to actually do it. Somebody asked what everybody’s favorite YouTube helicopter videos were, and mine is, hands down, the Oh Ye of Little Faith Apache video (which you can see as part of the CRM lesson plan). That’s a pretty classic example of a CRM fail, but it doesn’t have to be so overt: consider the Bonanza video where they almost whack a mountain in IIMC.


That’s exactly the kind of scenario that will bite you in the ass. Everybody in that airplane was clinching sphincters long before they kissed that hill, but either nobody said anything or somebody didn’t listen. CRM fail.

So in the ground lessons section, I’ve placed the MRS and CRM lessons where I think they ought to be relative to each other: CRM up front, and MRS stuck somewhere in the back. I bet you can make it through your PPL without being able to list the 3 kinds of rotor systems. And I think you could tuck them into the Aerodynamics lesson somewhere in the middle of your training just fine. Weight and Balance, Weather, Performance: all more important, and things you should be doing before every flight by the time you’re hovering. I think I know why MRS is on page 1-1: it’s a starting place for establishing a common language between instructors and students so they can go on to learn the more complicated stuff. And, from a marketing standpoint, it’s better to start off saying “Today you’ll fly a helicopter with a semi-rigid rotor system, but one day you could be flying a BO-105 doing loops in with it’s rigid rotor!” than starting off by saying “You very well could die flying helicopters.” Ironically, by handling ADM/CRM the way it is handled, the chances of that are probably higher.