Sunday, September 28, 2008

The Basics

My student and I noticed that the weather was threatening before we took off, and were doing our maneuvers just outside of the Class D airspace while we kept an eye on it. If it moved in really quickly we could divert downwind. We let the tower know what we were up to, too. It didn't take long for Ken (the controller) to call us and say "The National Weather Service just called on the phone. They say that storm to the southwest has surface winds gusting to 35." We entered the pattern and landed while the storm was still pretty far away.

The storm looked a lot closer while we taxied, and I told Dan "Let's tie it down before we do any debriefing." I took the picture above as we walked in. The Bonanza in the foreground was not tied down. Aha, I thought, a good chance to show my student how aviators, like sailors, take care of each other.

"I'll bet that Bonanza pilot would sure appreciate being moved to a tiedown," I mentioned to the linemen sitting at the desk.

"Nah, he never ties it down." And that was the end of it. They wouldn't let me move the Bonanza, either, for fear of liability.

I thought back to last summer when Landmark Aviation in Sioux Falls called my cell phone while I was enjoying a capuccino downtown.

"We just got a tornado warning. Do you want the airplane put into a hangar?" You bet I did.

Customer service is in a state of flux these days. Too often, it means that the customer provides the service. But in aviation we're supposed to help each other, no matter what.

A few weeks ago, the airplane in the picture to the right was waiting when I arrived at the airport. There was some kind of mixup about whether the FBO had the proper pneumatic starter. The pilot, wearing a NASA jumpsuit, mentioned something about "your new T-38 monument" unless the starter was found.

The T-38 was still there when my student and I landed. It was lunchtime. I approached the pilot, who looked kind of familiar.

"Hey, listen, we treat stranded pilots right around here. My student and I are headed to lunch; it's a pretty good Mexican restaurant. Wanna join us?"

"Thanks, but they say they're gonna get me started in 15 minutes or so, and I'm already late." Of course...and when someone who gets a T-38 for personal transportation is late, it means millions of government dollars.

But we chatted for a while. He was an astronaut who had commanded a shuttle mission. I was pleased to be in a position to offer help.


The T-38 wasn't tied down, either.

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Friday, September 26, 2008


It's common sense: make sure that your navigation equipment works before you fly. There are a few cases where this doesn't matter, like when you are flying locally using pilotage alone, but certainly if you are going to be flying at night, in the clouds, or over large bodies of water you want to know that the black boxes are telling you the right thing.

This is an old lesson. World War I ace and head of Eastern Air Lines Eddie Rickenbacker learned it the hard way, in 1942. This story comes from Seven Came Through, published by Doubleday in 1943.

It was the height of World War II, and Rickenbacker was on a secret mission to inspect all air combat groups. After a fact-finding tour of the European theatre, he headed to Hawai'i to begin inspection of the Pacific. His first destination was "1800 miles southwest" of Hawai'i; it was still wartime when the book was published, and Rickenbacker was a little coy about the destination. My best guess for the destination is Howland Island, which is famous because another prominent aviatrix, Amelia Earhart, never made it there, either.

The Army Air Corps assigned a B-17 and a crew to the flight, and they left Hickam Field in Honolulu on October 21, 1942. The departure didn't go well; a brake problem on the right main caused a groundloop.

Nobody was hurt, so the Army dug up another airplane and they launched again, crossing the ocean using dead reckoning and an octant. An octant works like a sextant, but uses one-eighth of a circle rather than one-sixth. The problem with dead reckoning over the ocean is that you can't determine drift or groundspeed, so you depend on the accuracy of the winds aloft forecast. We all know how that goes. But the octant and navigator were there for backup.

The octant had been loose on the navigation table aft of the cockpit during the groundloop, and had fallen. Damage from the fall made it inaccurate. With no way to find the destination island (whose direction finding equipment wasn't working), the B-17 eventually ditched. All eight made it into the rafts, but one crewmember died before they were rescued. Twenty one days later.

Only a few luddites use celestial navigation in airplanes anymore. I've tried, but every time I go up the hill and take sights I end up knocking on my neighbor's door and asking when did you move to Montana? Where is the lesson for us?

In the USA, the Federal Aviation Regulations (14CFR) require regular checks of pitot-static (14CFR91.411) and VOR navigation systems (14CFR91.171). The magnetic compass should be checked with each annual inspection. We all know people who don't do the checks, and I can't tell you with a straight face that skipping a VOR check will make you spend 21 days in a raft.

Besides, I hear people say, nobody uses that stuff anyway. Now it's GPS, GPS, and when that fails GPS. How do you check the GPS?

First, let's get this out of the way: GPS can fail. Satellites have broken down. The military test jamming equipment. Incorrect almanacs have probably been uploaded. Ionospheric storms hit with shocking regularity and little or no warning. Antenna connections break. Voltage spikes fry avionics. Batteries leak in handhelds. The system is guaranteed to be 99.999% ("five nines") reliable, but there are 100,000 North Atlantic crossings every year, so statistically one of them will have GPS failure.

What do we do about GPS failure?

The big expensive answer is WAAS, which I will leave to a future blog entry.

The simplest answer is that we cross check against other systems, usually pilotage and VOR/DME. (When I flew turboprops I carried WAC charts, partially for sightseeing and partially "just in case.")

The newest answer is you are required to check GPS integrity before every flight using RNAV (DPs, STARs, Q- and T-routes). This is called a RAIM check (Receiver Autonomous Integrity Monitoring). It requires at least five satellites (and barometric altimeter input). See this post for an explanation.

The requirement has always been there, but it was scattered through a lot of supplemental documents like TSOs and operating manuals. Now the FAA has clarified the requirement, in a new issue of Advisory Circular 90-100. They have even given you a website to help you do it. If worse comes to worse, you can get the information from Flight Service.

Even if it's not required for your operation, it sounds like a good idea.

Modesty aside, I feel strongly enough about the study of the art of navigation that I wrote a book: Understanding Mathematics for Aircraft Navigation. Some people say that it contains more than pilots need to know. I've already said how I feel about that...

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Thursday, September 18, 2008

Energy Crisis

It's the oldest debate in aviation: does elevator control airspeed or does it control altitude? Does power control altitude or does it control airspeed?

Come to think of it, "Who gets left seat?" may be an older debate. But this one is more fun.

Every flight instructor struggles with it. The student asks, and the instructor hems and haws and says things that start "Well, sometimes ...," or draws out a long list of conditionals ("If you're high and the airplane is slow and it's a Tuesday in the northern hemisphere, then you should ..."). Is there a simple answer?

I used to use a flip answer: "Power and pitch control airspeed and altitude; you have to stay coordinated." Well, it's not really flip, but it's not really useful, either. So, it there a useful simple answer?

I believe that I have stumbled on one, in a roundabout way. Let's back up a little bit to another classic instructor - student dialog. The instructor asks how to recover from a stall. The student is confused, because the FAA's publications, followed by the commercial publications, use a lot of flowery folderol about turbulent flow and burbling air to talk about why an airplane stalls rather than saying what a stall is. The thing is, when you give a student the correct definition of stall, it includes the recovery:

  • A stall means that the angle of attack is too high, so
  • A recovery means reducing the angle of attack.

  • Students who have been exposed to this have a dangerous attitude about stall recovery, because they do not have a clear idea that it's pitch, not power, that will save the day. So here's a typical dialog:

    Me: How do you recover from a stall?

    Student: Add power and ...

    Me, interrupting: What do we do in gliders?.

    Power has almost nothing to do with stall recovery; stall recovery means reducing the angle of attack. You need power to pull your scared bellybutton away from the ground. (Admittedly, power slightly reduces the stall speed of many light aircraft, so it may in fact aid stall recovery, but that is a secondary effect.)

    So now let us return to the original debate. The solution to the conundrum is to examine the nature of power. Power becomes one of the four forces, namely thrust, although it also involves a small amount of lift at higher deck angles. A force means that there is a change in energy.

    Energy is the key.

    There are two kinds of energy, potential energy, which is proportional to height, and kinetic energy, which is proportional to the square of speed. Energy is conserved, so if you lose one you have to gain the other. "Trading airspeed for altitude" is how gliders go around; "trading altitude for airspeed" is a favorite chant of airshow announcers, watching some tiny 9G biplane in a screaming dive toward the bottom of the box.

    But energy changes. The only way to change the energy is to exert a force. Two of the four forces are important here. Drag tends to reduce energy: it slows you down. That's why gliders are so small and sleek. The reduced drag means that the glider retains more energy. How reduced is the drag? A Cessna 172's lift over drag ratio is about 10:1. My glider's lift over drag is 39:1. At the same weight, the glider has 1/4 of the drag!

    The other force is thrust, which tends to increase energy. Thrust speeds you up. No, wait, thrust makes you go up. It's both! Thrust adds energy, which can be in the form of speed (kinetic energy) or altitude (potential energy).

    Gliders don't have thrust, and depend on rising air to gain energy. Airplanes can gain a little energy this way, but usually depend on stored chemical energy (in other words, fuel that is converted to kinetic or potential energy.

    But you knew this already: "An airplane climbs because of excess thrust." A climb increases the airplane's energy.

    And so we come to the definitive (pardon my hubris) answer on power management during approaches.

  • If the energy is low, add power;
  • If the energy is high, reduce power.

    In practical terms:

    Add power when you are low and slow; you need a lot of energy.

    Reduce power if the PAPI is all white; you are high, so you have too much energy.

    Leave the power alone if you are low and fast. Raise the nose to convert airspeed into altitude. Just don't let the speed get too low.

    Leave the power alone if you are high and slow. Lower the nose to gain speed, and you will lose altitude.

    If we could only find a simple rule for the price of oil.

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  • Monday, September 15, 2008

    For want of a nail...

    The midsized jet had arrived the night before. It had diverted from where its passengers would be waiting because of a NOTAMed closure.

    So now it was early Sunday morning. The jet crew in their epaulets stood out from the usual bluejeaned airport bums, and while they weren't aloof, they were busy with ice and coffee and fuel.

    My student and I walked out to the 172. The air was dead calm; the only clouds were contrails high above. The cool fall air was just right, especially after the heat of the summer. This was to be the student's third flight, and we did a careful preflight. We talked softly. There was no wind, no noise, nothing moved.

    A buzz in the distance became a helicopter. Our radio was off, so we just watched it fly past at 100 feet or so. "Who's doing a practice approach?", I wondered. It did not look familiar. It flew along the runway, getting louder, and I marvelled again at the Doppler shift as it passed. It was the same type that my wife and I rode in a spectacular aerial tour of Hawai'i many years ago.

    Passing even with the jet, it made a left turn. My eye followed its path, and I could see the jet crew running toward the plane. "They must be afraid of the rotorwash," I thought, but they just stood by the airstair door and watched. The helicopter passed in front of the jet, turned left again, and settled in a circular cloud of dust. The crew stood and watched.

    The helicopter shut down and a long line of passengers walked over to the jet, dropping their luggage at the hell-hole. There was a lot. The crew pitched the bags into the hell-hole (were those golf clubs?), got in, and fired up.

    "November blah-blah-blah [they've blocked their callsign, so I'll respect their privacy], cleared to the [someplace really nice] airport via as filed blah-blah-blah."

    And they were gone.

    But not for long.

    "Tower, [midsized jet], we need to return."

    They couldn't get the gear up. Too much of a wet print to continue.

    So they taxied to the ramp and called a mechanic, not from the FBO. A quick inspection found that the nose gear had been turned too far in one direction, bending something. This is pretty common; many airplanes have red stripes on the nose gear that mark the travel limits. The King Air has a neat system of vertically aligned circles made from a softer metal; if the circles aren't lined up, the gear was turned too far.

    I don't know what the midsized jet had, but the line crew turned the wheels too far, and the flight crew didn't catch it, and the passengers had to cool their heels before heading to someplace really nice where you would like to be right now.

    Let's split the blame 50-50. I just want to be sure that the next time my 50 happens I catch it before takeoff.

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    Thursday, September 11, 2008


    I had Flight Lesson Number One with a student today, and it got me thinking. I know a lot of pilots who are burned out on aviation. This is not the same as being burned out on flying, but the former can easily become the latter. One friend has it so bad that his new goal is to work as an FAA inspector. But this student was overflowing with enthusiasm. That seems to be the antidote.

    Whatever the occupation, people burn out on it. Teachers and health workers are particularly susceptible. I had an early lesson on this when I was in graduate school. A few of us were sitting around one evening with John Wermer, a very nice man, a gracious host, and one of the leading mathematicians of his generation. We were grading calculus exams. He said, "You know, I have been teaching calculus for 30 years, and I learn something new every year." I adopted that attitude on the spot. And now that I have been teaching calculus for 30 years, I can make the same claim.

    Pilots and academics share the attitude that teaching is somehow below them, that it is something that one does because it is required. At the extreme end, I know one pilot who got his jet job, and as soon as his last student was finished, he nailed his Instructor certificate to a fence post and blasted it to smithereens with a .22 rifle. And I remember at least one prominent academic announcing "No undergraduate has ever written a paper that it was worth my time to read." You get the idea.

    But the sad thing is that teaching is not a step down; it is a step up. Teaching exposes you to people like this morning's students (both math and flying), who were so full of enthusiasm and the pleasure of learning something new.

    Enthusiasm, like gloom, is contagious. Choose wisely which one you share.

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    Monday, September 8, 2008

    Airship Surprise

    Last month when my wife and kids and I were in Boston (where I grew up), I told them about the Hindenburg flying overhead at 1000 feet on its way to Lakehurst. (My parents do not remember this, but I have read it in several places.) The ship was over 800 feet long, so the Hindenberg at 1,000 was kind of like a Taylorcraft over the city at 20 feet. Man, I would love to have seen that...

    While I was glider flying on Saturday (a personal best, 3.1 hours in the Jantar, including almost 20 miles of straight-and-level (!) along the ridge), my wife and my kids were shopping. (How many millions of guys have said that before?) This evening after dinner, my daughter sat down next to me and said "We got you a present," and handed me a small package. "It only cost a dollar," she added, like it was no big deal.

    The package consisted of a dozen or so small black-and-white photographs of Boston, taken in the 1930s. The focus was super-sharp, and although each one had a hand-written caption, I identified each sight as we fanned through them. "Wow, honey, these are really nice," I said. Sincerely.

    Then I hit one that was a picture of the Boston skyline. The most recognizable building was the Custom House. This one had what appeared to be a smudge or maybe a lenticular cloud above the skyline. I took off my glasses for a closer look.

    The smudge was an airship.

    I strained to see. Was that a swastika on the tail? It was very, very small, and even my world-class closeup vision couldn't resolve it. I ran through the house, looking for a magnifying glass. From my son's bug collection? Couldn't find it. From the Oxford English Dictionary? Wrong edition. I remembered that there was a small magnifier in my compass.

    I took the photo into the brightest room in the house, the one with the world's most power-hungry light fixture that nobody ever turns off. I focused the glass on the tail of the airship.

    "It's the Hindenburg!" I literally jumped for joy. "The Hindenburg! You got me a picture of the Hindenburg!"

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    Thursday, September 4, 2008

    Missing the Signs

    The last week or so seemed to be a time where I was really helping my students in ways that I might not have predicted. This goes for flying and for my university teaching, too. It's the second week of the semester and I have already given individual help to more students than all of last semester.

    In particular, Dennis had learned to flare, and it was time for him to solo. We talked about it after we shut down, and he was a little tired, but I suggested that the paperwork would take long enough for him to perk up. And I was right. By the time I got all the signoffs done he was rarin' to go.

    I walked him out to the airplane, he started up, and I walked calmly back to the office. At least that's how I was hoping it looked. I told the airport bums that he was soloing, and we all stood at the window. Dennis stayed still. "Running the checklist," I said. But he stayed put for longer. Was he getting cold feet?

    After about 5 minutes, he shut down.

    I stuck my hands in my pockets and ambled out to the airplane, wishing I had a blade of hay or something to chew on to make me look nonchalant. Did he get cold feet? Should I make a joke?

    "The radios won't come on," he shouted out the window. Oh.

    I crawled under the panel and poked around, but made no progress, so we called maintenance, and someone came out and confirmed that the avionics master had failed. (I later found out that other instructors had had trouble with it, but had not told maintenance. I think this is poor airmanship.)

    So we scheduled again for an early morning. I was thinking that there would be light winds, a good time to solo. "But," I said, "let me ride around with you a couple of times to make sure nothing happened to your skills overnight."

    At morning the windsock was hanging straight down. Perfect! Dennis did his preflight, we started up, and taxied. An open hangar door revealed the nose of a red Stearman, so I taxied while he admired it. A great day to be at the airport. He did the runup and he taxied to the hold short line. "Hold short awaiting landing traffic," the tower said, and we could see the regional jet about three miles out.

    "Look how he's manhandling that airplane," I said, "must be a new first officer." The nose was going up and down, there was yaw, there was roll, although the jet appeared to stay on the glideslope. The regionals are still hiring, and there are a lot of inexperienced pilots flying these things. I've written about this before; see Look Who's In the Right Seat.

    Dennis and I launched, and I was surprised. He was all over the place! On base, the airspeed was varying by 10 knots either side of the target, and he flew through final, although he recovered to make a decent touchdown. What happened overnight?

    "Let me try one," I said. I was all over the place! On base, the airspeed was varying by 9.5 knots (hey, I was a little better) either side of the target, and I flew through final, although I recovered to make a decent touchdown.

    "Let's call it quits," I said, and he agreed without hesitation. It was a terrible day to solo.

    So what happened? We had missed a couple of big cues. First, was the cloud pictured here, showing some significant shear at altitude; there were multiple shear layers, down to the surface.

    The second cue was the RJ. Watching it point all over the sky led me to believe that the pilot was the problem. By contrast, once when I was flying Life Flight I noticed a PIREP (pilot report) of severe icing, reported by an RJ. Severe icing is pretty rare, and since I decided that it was unlikely that a professional jet crew had forgotten to turn on the anti-ice equipment, I treated the report as reliable, and spent a fair amount of time investigating. But that was then; this time, I allowed prejudice to help me reach an easy conclusion.

    And I was wrong. It wasn't the pilot, it was the atmosphere. And I missed it.

    Prejudice and aviation do not mix.

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