Thursday, July 31, 2008

Lost Luggage

My flying club gives you a few minutes of free flight time as part of your monthly dues, and even though this week I have seen both the Pacific Ocean and Lake Huron, I hate to pass up free flying. It's the last day of the month...I just had to have that $100 hamburger.

First I flew with a student, then invited him along (as long as he was buying lunch). Oh, and doing the flight planning, too! I also told him to invite some friends, because we were in the Cherokee Six. But nobody could go on short notice.

There's a good restaurant run by one of my former students at Twin Falls, ID.

We had a nice flight to Twin. Dennis enjoyed the 300 horsepower takeoff and did all the navigating, and pretty soon we were hearing "Taxi to the ramp via Alpha, monitor ground." I was looking around as we taxied, and noticed a red Cessna 172 with beacon, landing light, and engine going, and made a mental note to watch in case he tried to take the same taxiway we did. Something didn't look quite right about the airplane but I couldn't determine what exactly it was.

But he was slow to start moving, and we pulled into the ramp as he called "Twin Falls Ground, Cessna xxxWM on the ramp, ready to taxi." While ground gave him the wind and altimeter, I finally figured out what didn't look right: there were two suitcases on the ramp next to him.

"Whiskey Mike," I keyed the mike, "There are a couple of suitcases on the ramp next to you."

"Calling Ground, say again." The controller sounded angry. But I didn't reply.

"Ground, Whiskey Mike, I'm going to, ah, hold position here for a minute."

"Whiskey Mike, roger."

And Whiskey Mike got out of the airplane with the engine running and reloaded his bags. He got out with the engine running.

This time, nothing happened, but a couple of years ago at home a Dakota pilot was mistaken in thinking that the brake would hold, and his airplane made 7 perfect slices in the fuselage of the 210 in front of it before enough other airplane parts merged to stop the whole process. The 210 looked like a fish ready to grill. But the only thing that got grilled was the Dakota pilot, because there was a Fed waiting to fly the 210 as part of a 135 flight check.

If you're going to chew up airplanes, it is usually wiser to avoid chewing up airplanes with Feds on board.

I used to own a Taylorcraft, and I hand propped it many times by myself. Brake on. Left main chocked. Right main chocked. Check chocks. Pull airplane by prop to see if it is movable. Check the throttle. Check the throttle again. Mags on, swing the prop, walk slowly and deliberately to the cockpit. I never had a problem, but I never deviated from the procedure, either.

I was careful. The Cessna pilot was lucky. The Dakota pilot learned a lot during his 30 day suspension.

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Wednesday, July 23, 2008

It's Not the Heat, It's the Humidity

What's with the flight instructors and density altitude? Sometimes it seems like all we every say is "Right rudder! Density altitude! Centerline!"

But our job is to remind everyone about the things that don't necessarily come up every day, like engine failures, flying by instruments, and unusual weather.

For the record, density altitude is the pressure altitude corrected for temperature in accordance with the International Standard Atmosphere (ISA), which converts between density and altitude in standard air. Heat changes the density of the air, so you calculate the density and use the ISA table backwards to interpret that density as an altitude. You learned this in pilot training, and maybe even saw a Koch Chart

Too much math for most folks.

I live in high desert country, 4500 feet above sea level and dry. Summertime high temperatures are usually over 90F, or about 32C, so the density altitude is often around 7500 feet. This is normal for us.

But density altitude is sneaky, as we discovered the other evening. We were flying in the evening because it was cooler. Cooler air means lower density altitude, so we should climb better at 7pm than we would have at noon, right? But the airplane barely climbed.

Earlier that afternoon I had gone for one of my usual runs. One of the pleasures of running in this climate is that perspiration evaporates almost immediately, but that day the sweat was pouring off my bald head and stinging my eyes. The dewpoint, which is usually around 0C, was 19C! This meant a relative humidity of about 70%.

And that's the problem: humidity. You'll notice that the Koch chart does not mention humidity! But my worst density altitude encounters have been due to humidity, not heat. The worst was in the lush part of New Jersey, in a Mooney. There was a deer on the runway, so I went around, but the Mooney wouldn't climb. This was at sea level, the temperature was probably near 85F/30C, but the humidity must have been around 95%. The Koch chart would say that the density altitude effect was small, especially compared to the effect of 30C at 5000 feet MSL. But that doesn't reflect the true density of the air. Koch may not have known this, but the Mooney did.

[All together now] It's not the heat, it's the humidity.

My student that night is a retired chemist, and he understood this right away. "The atmosphere is mostly Nitrogen," he said, "with molecular weight 28. But water has a molecular weight of 18. That's a big difference!"


Now for a little basic aerodynamics. You climb at a high angle of attack, where Newton's Law (every action has an equal and opposite reaction) dominates. In other words, air molecules hit the wing from below, so it goes up. Momentum is conserved, so an 18 unit mass transfers about 35% less momentum to the wing than a 28 unit mass transfers. In other words, if we flew in pure water vapor, the wing would produce 65% of the lift. This is the difference between 15,000 feet and 25,000 feet in ISA!

Wikipedia had complete nonsense about this in the "Density Altitude" article. I fixed it.

Just wait until winter, when I'll start in on cold temperature altimeter errors...

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Sunday, July 20, 2008

Something Totally New

Well, totally new to me, in this case launching a glider behind a truck. This has been around for quite a while, which you probably already knew, but it is worthwhile to celebrate the fact that after 25 years in aviation there is still new territory to explore.

Our tow pilot never showed yesterday, so someone got the bright idea of practicing ground launch. Only one pilot in the bunch has the necessary logbook endorsement, but he volunteered to sit in the back of the Blanik and show everyone how it went. It was a good day for it, with no wind at the surface and no noticeable change in the wind with climb. The airport was quiet. We reviewed the speed calculation (at least I could do a little instruction). Let's go! But I have never seen a bunch of pilots so reluctant to fly. Why? A lot of it is the huge amount of superstition about ground launch. I tried to tell myself that it was like an MU-2: not inherently dangerous, just different. Flying judgments based on superstition are no different than judgments based on superstition in any other area of life.

There was a little bit of bravado in the hangar. People asked me, as the "instructor", what I though of ground launch. "I have no experience," I said, "so how can I compare something I have done with something that I have not done?" There was a murmur of agreement. "On the other hand, when I was a little kid I heard about there being two ways of doing something [I tried to make my voice a little dusky here], but even with no experience I knew right away that I preferred one of them." This got a laugh.

I questioned my own reluctance to fly. I had an excuse: if I left early I could go to the EAA chapter meeting. No, wait, they met last night. I had another excuse: my zipper had failed, and I was running around with my fly open. Like anybody cared around the airport. But, if we did a bunch of flying then we would want to go out to dinner and how could I go out to dinner with my fly open? This was clearly unacceptable!

My motives were not pure. I was making excuses. People have been ground launching for years (hint: how did the Wright Brothers get airborne at Kill Devils Hill?). Tim had been doing it for years, we had all the right equipment, and the right number of people. Time to be the samurai and volunteer to go first.

So we climbed into the Blanik, Tim in back and me in front, with my zipper open. We did the checks and gave the signals. I had no idea what to expect. I had no idea what to expect! It has been a while since I said that in an aircraft.

We were too slow on the first one, and only got to about 400' before the truck ran out of runway. I looked at the wingtip's angle against the horizon; the angle was far less than the 45 degrees that I had been told to expect. We released, Tim gave me the controls, I wandered around a little (remember, we were pretty low), and landed. If nothing else, low level maneuvering in a glider is good practice for landing out.

We did a quick analysis and decided that the truck had to go faster. And now it was my turn to try it.

It was not that difficult. My initial climb was slow, dragging the rope, and that meant more friction and less final altitude, but we got off the line at about 700' above the airport. This was enough to try to work a little bit of lift, but still we were back on the ground in a few minutes.

Now it was fun. I pulled a little more strongly the next time, got the rope off the ground, and transitioned into the 45 degree climb. We were right at the maximum speed, which was good. Another one gave me a good feel.

I decided that it was someone else's turn, mostly because I felt that as the instructor I needed to experience what the ground crew was doing. Adam got into the glider, I got into the truck, we hooked up, and off we went. The glider seemed to hang in the air directly above us. They released, I released, and we drove off the end of the runway.

But they broke the weak link, so that was the end of flying for the day. Ground launch involves forces on the glider that the pilot cannot feel, so we use weak links in the rope to make sure that it breaks before the glider does. That's different from aero tow. Not dangerous, just different.

Ground launch requires everyone to pay closer attention to details. The goal is perfection. A lot of aviation problems would disappear if everyone aimed for perfection.

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Saturday, July 12, 2008


We came in high from the west, the sun directly behind us, the clock's hands at the same position as when we had departed. Our shadow played across the landscape. The water of the lake below was still. Some parts were more still, making a patterns like complicated kanji. White hulls were bright in the low sunlight. Some wakes were like razor cuts, straight and clean. Some wakes were paired, the second curling back and forth across the first. The water skiers themselves were too small to see.

As we crossed the shore there was a line of white pelicans, spaced with eerie precision, each riding the vortex of the one ahead. Their wings did not move. The radio was silent.

The light shone bright off the closed hangar doors. It was the light of Provençe, shining hard and straight and horizontal. It seemed to pass right through things at the same time as it highlighted them. It outlined every pebble. Tire tracks in the gravel glowed with an extra dimension. The edge of the pavement appeared ragged as we passed overhead, and the paint on the runway had texture. Our shadow grew larger to our right, its blackness making the grass by the runway a limpid emerald green.

That is why we fly.

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Friday, July 11, 2008

Single Seat Instruction

That title is an oxymoron: who is your student in this single seat aircraft? Yourself, of course!

One of the ironies of teaching is that it is impossible to do directly. A teacher can organize important facts and present them coherently, but that's rote, the lowest level of learning. The real craft of teaching is arranging a series of experiences through which the student comes to understand. "Learning is a change in behavior due to experience," according to the FAA. This is one thing that they got right. In other words, you have to lead the student to a place from which he or she can learn.

The FAA likes the Socratic Method, where the student is led to understanding by a series of questions. (They seem ignorant of the idea that Socrates probably had Asperger's Syndrome.)

So how do you teach yourself? It's pushing a rope, because you don't really know the destination (if you did, then you wouldn't need to be taught). The best you can do is arrange a series of experiences, kind of like experiments, and then contemplate the results. In some areas, reading or calculating might be enough, but in flying there's the John Dewey tension between action and contemplation: neither suffices.

You also need to avoid experiments that will kill you. That's why a pilot certificate is a "license to learn:" you know to avoid a lot of danger.

Right now, I am teaching myself to fly a my single-seat glider; see my previous post. Thanks to Brad and Larry, I managed another flight yesterday. Listen in on the debrief...

Salviati: How was your flight?

Simplicio: Fun.

Salvi. Fun? Did you improve?

Simp. Yes. My coordination was much better. I remembered to let off on the rudder after rolling into or out of a bank. The yaw string spent much more time in the center.

Salvi. Excellent! What else?

Simp. I still have not mastered seeing my pitch attitude in a turn. This is difficult near the mountains, but I should do better.

Salvi. How do you know that you haven't mastered this skill?

Simp. I got some stall burbles while thermalling.

Salvi. [Oooff!] You must learn from this. What else have you learned?

Simp. This is an old lesson. I was fumbling around looking for a place to write down my takeoff time and release height, and I lost a lot of altitude.

Salvi. Yes, you must focus on the task at hand. That is like losing fuel through some silly error like forgetting a fuel cap.

Simp. There is one more thing. There is interference between the radio and the variometer. A few seconds after beginning to transmit, the vario indicates 1000 feet per minute in climb. At first I chased these false climbs, but I learned not to. [I think that the draw from the transmitter reduces the battery voltage below the reference voltage for the vario.]

Salvi. Well done. What about your landing?

Simp. [blushes] The glider came to a stop at exactly the point that I had told Brad before the flight.

Salvi. Excellent! How did you achieve this mastery?

Simp. I remembered that the dive brakes are very powerful, so flew the pattern with less drag. Then I added drag when I decided to touch down. I did not get so nose low during the rollout, so lost less energy.

Salvi. And the touchdown?

Simp. [blushes] Main and tailwheel touched at the same time, and there was no bounce. There was a little weathervaning from the crosswind, but I fixed that. I did not get so nose low during the rollout, so lost less energy.

Salvi. Excellent! What else?

Simp. I had a low-altitude save. Not scary low, but 200 feet above pattern altitude. I would not have tried this in the Blanik, but I felt that this ship could safely try a circle in lift that low. I gained 4000 feet from there.

Salvi. Excellent! There may be hope for you yet.

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Sunday, July 6, 2008

Flight Following

[This is an article I wrote for our local EAA Chapter newsletter. We have a fantastic newsletter with a lot of useful information. The style here is a little more technical than what I usually write, but I think the story is useful. Your comments would be appreciated.]

I was chatting with a chapter member about a recent trip. He told me that the hardest part of the trip had been flying through the airspace around Salt Lake City International Airport. He swore that he would never ask for flight following again: "They kept sending me to all kinds of places where I didn't want to go."

Air Traffic Control (ATC) provides flight following (technically, radar traffic advisories) at the cost of some convenience; in the end, do they help or hinder the VFR pilot? He says they hinder; I say they help. Let's see why I think the way I do.

First, why does ATC reroute us? The answer is pretty simple: they are shooting big fast airplanes into the sky, and they don't want to hit us. Salt Lake International averages almost 1200 flights a day, and at the busy times they have more than one IFR airplane taking off every minute. They also have F-16s and other military airplanes headed in and out of Hill Air Force Base. This is a flak barrage for any airplane passing through the area. So, the controllers ask VFR airplanes to move for their own good.

You can legally go through the area at 10,500 MSL without talking to ATC (as long as you have a working Mode C transponder), but you might as well wander through a mine field. Airplanes arriving at SLC are at 11,000; airplanes leaving SLC are at 10,000; at 10,500, you are squeezed in between them like a Taylorcraft sandwich.

So, your reward for getting flight following and squawking the code and holding altitude and holding heading and accepting a minor reroute is that ATC won't shoot any 106.00-calibre bullets at you (that's the fuselage diameter of a SkyWest RJ). When the controllers point out the heavy jet indicating 300 knots that will pass 500 feet above you, or the trio of F-16s that will pass 500 feet below, you get a free air show instead of a scare.

Another reason to accept the reroute is that it is not that bad. A perpendicular diversion of 37 miles only adds one mile to a 700 mile trip! So you might as well enjoy the sightseeing and the free air show. You can reduce this even more if you know where ATC likes to send VFR airplanes (for example, Mountain Road east of Salt Lake City), and aim for that from the beginning.

Sometimes ATC provides shortcuts. Las Vegas has complicated airspace, and several times I have had controllers suggest a shortcut that I did not think would be available. I came out ahead with flight following.

Flight following is the biggest help when you need it the most, that is, when you have a problem. ATC can help you find the nearest airport, and coordinate rescue efforts. You will also hear about weather problems, temporary flight restrictions, of other factors affecting your flight right away.

Some pilots don't like talking on the radio. The advantages of flight following may make it worth the effort to improve. The Aeronautical Information Manual (AIM) has all of the rules, but the first rule is to listen before you talk, so you have a sense of what is going on. Your first call should say who you are calling, who you are, where you are, and what you want: "Salt Lake Center, Archer 12345, 20 north of Malad, request flight following." After that, listen to what the controller asks you to do. This can range from something simple like "Say altitude" to something more complex like "Maintain 8 thousand while in Class Bravo airspace." Controllers always say things exactly the same way, so once you have gone through the drill once or twice you will know what to expect. Talking to someone who has done it can also make it easier. And, you can listen to ATC during your local flying.

The worst thing that you can do on the radio is get angry. It is perfectly OK, and even expected, to question a controller's request, if you have a good reason. What's a good reason? If they steer you toward the mountains at an uncomfortably low altitude, you should ask about it. Or if they give you a heading into a cloud (VFR), you should politely tell them; they will make another plan. Just say, "Approach, 56X, we won't be able to stay VFR on this heading." Nothing fancy; just be clear and concise.

And don't think that you are bothering anybody by asking. Controllers get their satisfaction from talking with pilots and helping them on their way. They WANT to talk with you! So give them a call.

Wednesday, July 2, 2008

The radio, and the telephone, and the movies...

...that we know may just be passing fancies, and in time may go... [Gershwin, Our Love is Here to Stay]. Here's Ella Fitzgerald's version; listen while you read.

Gershwin didn't have the internet, of course.

But my students do. How should they get a preflight weather briefing, or file a flight plan? What part of the process is "here to stay?"

The answers to these questions are continually evolving, and I have had a few friendly debates with other flight instructors about what to do in 2008.

When I was working on becoming a private pilot, and for quite some time afterward, I relied on the walk in briefing. Flight Service Stations were everywhere, almost, and you could talk to a real person, look at the synoptic charts and prog charts and plot the radar report on the little sectional with the squares to see where the precipitation was. You have seen the data for this, but may not know what it means. For example, here is a radar report from Grand Rapids for this afternoon:

GRR 2135 AREA 2TRWXX 20/101 199/44 142W MT 510 228/24 C2837
AREA 2TRWXX 276/101 248/106 27W C2837
AREA 3RW++ 284/134 75/114 175W MT 510 228/24
^HL3 IK25 IP1 JK56 JN2332 KJ55663433 LH1 LJ64565233 MJ4256665 NH56426565 OH146
OL65 OO3 PI6

What does "^HL3 IK25 IP1 JK56 JN2332 KJ55663433 LH1 LJ64565233 MJ4256665 NH56426565 OH146 OL65 OO3 PI6" mean? There used to be a copy of a local sectional on the briefing counter at each FSS, usually covered in plexiglas. A grid was drawn on the plexiglas. The letters HL, IK, JK, etc. indicated a starting grid square in each row, and the numbers indicated the strength of the returns in each grid square; these were written in the appropriate square with a grease pencil. So, in row L, starting with column J, the return strengths were 6, 4, 5, 6, 5, etc. Rows K, L, M, and N are pretty full; that's probably the area of heavy rain from 134 miles on the 284 radial to 114 miles on the 075 radial, but it's impossible to be sure without a copy of the grid.

When a walk-in briefing was impossible, you could get a telephone briefing. It used to be that you had to have the local number, or know how to look it up, but around 1989 we got the "Automated" FSS. The automation really just referred to the phone system, because now there was only one number (1-800-WX-BRIEF, the same as today).

You call, give them a flight plan, and ask for a "standard briefing." Simple, and this method still works today.

Once in the air, you could get a radio briefing. You found a nearby RCO (that is, Remote Communications Outlet) and got the information over the radio.

You should get better service from Flight Watch, which uses the same frequency (122.0 mHz) at low altitudes all over the USA.

See my previous post on the vagaries of radio briefings.

Around 1990, "official" briefings became available over the internet, first by dial-up, then by TELNET, and finally by ordinary TCP/IP in a browser. This was called DUATS for Direct User Access Terminal Service. There are two online providers, DUAT, and DUATS.

(The history should be well-known, but the Wikipedia article is pretty poor.)

At the beginning, pilots whined about how many pages of output these services provided, and how much of it was useless; I don't hear this so much anymore. A little time in a simple text editor cuts out the stuff you don't need, and you can print the rest. A later plain language function persists, and even though it was designed by one of my best friends as an undergraduate, I hate it. The undecoded METARs and TAFs are nicely aligned, and in many cases you can find what you need by a simple vertical scan. You have to read the whole text version, no matter what, which was unacceptable when I was flying freight or air ambulance.

The biggest advantage of online briefing is that you never hear "VFR flight not recommended." They say this even if you are filing IFR.

Most pilots I know use DUAT or DUATS for their briefings, but many instructors introduce students to the process by having them call FSS on the telephone. This always leaves the student flustered, because he or she is being forced to communicate in a still-foreign language. As a consequence, they don't get the briefing. They don't know what to write down and what to ignore, no matter how many times you rehearse this with them before the call.

In my mind, a telephone briefing is an emergency backup; my primary briefing is online. So, I have chosen to start my students out with online briefings, and go back and do telephone briefings later. The Law of Primacy, right?

And now comes a new method: the telephone and the radio have given way to "the movies." Some Garmin GPS units offer near-real-time weather through XM Satellite Radio. The pilot has become a self-briefer. This must be a handful without a good autopilot, or a good copilot, but it strikes me as a good handful.

Now we come to the end of the song: "The Rockies may crumble, Gibraltar may tumble, they're only made of clay."

Clay might be weaker than love, but it is stronger than airplanes.

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