Monday, May 30, 2011

My Little Runaway

Since I am a college professor, I say "It's more complicated than it appears" and "Wait until we have all the facts before we draw a conclusion" often. That's why I haven't said anything about AF447, except for one tweet about this post when it became clear that the aircraft had stalled. I felt that I was in no position to judge the flight crew or its actions. "It's more complicated than it appears," I thought, "Wait until we have all the facts."

I'm glad I waited. An article today in the German Der Spiegel raises some questions about the Airbus's automated flight control system. It appears that both of the Airbus's side sticks were commanding "nose down," as expected. But the nose didn't come down, and the horizontal stabilizer moved in the nose up direction. The captain evidently took a seat with a comment from one of the co-pilots like "Here, you try it!"

They did the right thing.

The airplane didn't.

I am hesitant to draw a conclusion about French aircraft and stabilizer trim, but it is tempting to see a relationship between the recent grounding of the Falcon 7X fleet and this report. A Falcon 7X had a pitch trim runaway, so the fleet was grounded. Good move.

Those of us who fly smaller airplanes might wonder why the flight controls didn't overpower the stabilizer trim. In some heavier airplanes (starting with the Lear 25), the stabilizer trim is much more powerful than the flight controls, especially in the situation where the whole stabilizer moves, rather than a tab (tabs are bad because in some situations at high airspeed they can cause control reversal). United lost a DC-8 in 1983 due to a mis-set stabilizer trim (NTSB data here). Alaska lost an MD-80 to a stabilizer trim problem. Next time you're around airliners look at the stabilizer: there are usually marks on the tail showing the maximum and minimum stabilizer position, so it can be verified during the walk-around.

I've had two pitch trim problems, neither one of which caused a crash. The first was in my Taylorcraft: I was a little too enthusiastic with the trim crank and pulled the cable off the pulley, leading to a full nose-up trim condition. The T-craft uses a single trim tab on the left elevator, and while it was annoying I had no trouble pushing the nose down and completing the pattern. After that I learned my lesson: I trimmed slowly (which is the right way), and told riders "That's the trim crank; don't touch it!" No problem.

The other was in a Seneca. The electric pitch trim wouldn't respond. I played with it for a while and, consistent with my philosophy that circuit breakers are for pulling but not for pushing, I used manual trim for the rest of the flight. Good thing: there was a short in the system, and there were sparks behind the panel.

I've also had an autopilot runaway, in a Cessna 414A. Wait, I've had two autopilot runaways, but the second was caused by a pilot with an unpleasant personality who wanted to see how I'd react. (He didn't last long with the company.) The real one was on the final leg of an air ambulance flight. It was about 0400 and the final leg was less than 50NM in night VFR conditions. But it was 0400 and I was tired. I engaged the autopilot and the nose shot up into the darkness. Huh? Whoa! Phew!. I hit the autopilot disconnect and lowered the nose.

But it was 0400, so I engaged the autopilot again. Huh? Whoa! I disconnected it and hand-flew the rest of the way home.


Monday, May 16, 2011

Time Travel

I was talking with a prospective instrument student this morning who, like most, was concerned about approaches. His home airport has three approaches, one VOR-DME and two RNAV, and I know that his airplane isn't equipped for the RNAV approaches. But that's irrelevant: approaches are the last thing he needs to worry about now.

Teaching instrument scan is one of the most challenging assignments I have ever faced. I've tried all sorts of things and maybe there are a few I haven't tried. The diagrams in the FAA Instrument Flying Handbook are of some use, but they can't duplicate the dynamic nature of the situation. One instructor impersonates a metronome, and the student is supposed to look at a different instrument at each tick. Another takes a pencil and taps each instrument in turn, saying "Look here!" "Look here!" "Look here!" (This one works pretty well, actually.)

When I was at my sharpest as an instrument pilot (alas, that was a while ago) I noticed something strange. The perception/reaction sequence seemed to get reversed. Typically, you would expect that first a needle would move, and then you would perceive the movement during your next pass around the panel, right? But when I was at my sharpest I found that I would look at an instrument and then it would move. (This isn't just me; I've heard this from others.) I used to tell my students that that was the goal for being instrument sharp.

I couldn't explain this. It couldn't be that my body sensed any motion, because I had pretty rigorously trained myself to tune out somatic stimuli. How did I know that the needle would move just before it did?

I think I have an answer, and it is going to sound quite strange and mystical, but I assure you that it is pretty solid science. You can read more in the April 25, 2011 issue of The New Yorker; the article is by staff writer Burkhard Bilger.

This explanation depends on two widely-recognized principles: first, the brain takes in more information than our conscious minds can process, so it selects what we attend to; and, second, there is some delay between an event in the world at large and our perception of that event. David Eagleman, a neuroscientist at Baylor University, studies the nature of consciousness, and has spent a lot of time trying to measure the interval between event and consciousness as well as what happens during that interval. This isn't filling cranial cavities with beans: he is using functional MRI to map the regions of the brain that become active in response to certain stimuli.

The short version is that the brain constructs a story around all of the data the senses bring in and merges all of this sensation data into the story. So here's what happens in instrument flying. Say that the airspeed starts to rise but you are conscious of gazing at the altimeter. Your brain perceives the change, and you travel back in time to the instant before the change occured, directing your consciousness to the airspeed indicator. Well, no, you don't travel back in time, but you don't travel ahead in time as quickly as you usually expect. A good neuroscientist like Eagleman could set up an experiment to see if the pilot's eye really moves to the airspeed indicator, or whether the change of conscious focus happens internally.

Instrument training teaches the brain that the airspeed needle movement is important and requires a change of focus, while the corresponding movement of the second hand on the panel clock is of no consequence and therefore should not be brought to attention. When you get it, it doesn't matter which instrument you focus on. Your brain perceives them all, and will let you know when one of them does something important.

If this is correct (and even I have my doubts) then it doesn't matter whether the instructor uses a metronome or a pen or a series of strings going from instrument to instrument that looks like some impossible cat's cradle position. What matters is that the instructor makes the brain attend to the instruments and that the student spends enough time practicing to lay down the neural pathways.

Our society likes speed, and you can certainly find accelerated this and superfast that. I've always had my doubts about accelerated training, though. I think it produces a different kind of knowledge than the slower variety produces. I'm not saying that the knowledge is inferior; in fact, it can be quite useful. But one has to understand that some kinds of knowledge just take time. National Football League coaches say that it takes 20 to 25 games before a new quarterback has the game "slow down" enough in order to make him effective; it's the same kind of thing.

My prospective student told me that he would like to fly every other week for some reason I couldn't quite follow. No matter.

"You'll never finish the rating at that pace."

Learning fades unless it is repeated, and two weeks between practice sessions is too long for an adult. The neural pathways would fade rather than be reinforced.

And every flight instructor knows this. Students who fly infrequently, at every level, drop out. You can speed things up a little (4 or even 5 flights a week), but not too much, and you just can't slow things down.

Even if you can travel backward in time.

Wednesday, May 11, 2011

Sled Ride

It's happened to every glider pilot: the day looks promising, but the tow is eerily smooth, and you can't find any lift even after trying every house thermal and other trick you know. You enter the pattern and land. "I got shot down," you say, or "I needed a relight." (I like the relight metaphor better because of its focus on energy.) Or "It was a sled ride."

This week's Aviation Week and Space Technology mentions the ultimate sled ride after Virgin Galactic's first test of the feathering mechanism for SpaceShip2, their commercial space tourism craft. They took a high tow, to 51,500' MSL. Then they pulled on the spoilers (the feather mechanism) and descended at 15,500 feet/min to 33,500' MSL. They didn't even look for lift: they just entered the pattern and landed. Flight time? 11 minutes, 5 seconds.

Now that's a sled ride.

A little closer to home, our glider club met last night and decided to look for a new trainer since our Blanik L-13 is grounded (along with the rest of the Blanik L-13's in the universe, including the one hanging form the terminal ceiling in Santiago, Chile). Sled rides are an important part of training, especially for newcomers learning to land. I hope we can get some soon.

Monday, May 2, 2011

Rescue Me

I have long been an advocate of VFR flight plans (see this post) but a recent Civil Air Patrol presentation to my EAA chapter reinforces the message. Thanks to Bobby Picker for sending me the data to share.

First, as we pilots know, a VFR flight plan has nothing to do with securing government permission to fly a specific route. It used to be in Australia that flying without a flight plan was "NoSAR," for "Search and Rescue." And search and rescue is the purpose. So let's refer to our flying as SAR and NoSAR.

According to the CAP, 60% of crash survivors are injured. The injuries are severe. They say that 81% will die if not located within 24 hours, and 94% will die if not located within 48 hours. Being uninjured doesn't improve your odds much: 50% die within 72 hours.

Of course it won't happen to you, which is what my late friend Blake (thousands of hours, flown everything) probably thought last month. Yes, it can happen to you.

So how long does it take to get rescued? That's where flying SAR comes into play. Here's the data on how long it takes to start the rescue process:

SAR status
time to AFRCC notification time to rescue
15.6 hours if no flight plan filed 62.6 hours
3.9 hours if a VFR flight plan filed 18.2 hours
1.1 hours if an IFR flight plan filed 11.5 hours

Rescuers talk about the Golden Hour: quick rescue prevents death. NoSAR flying leaves you nowhere close. And even the best rescue - from an IFR flight plan - makes some survival preparation look attractive.

The CAP recommends that you should always file IFR, but in my part of the world that's not always an option. Last week I took a pilot friend visiting from back east to Afton, WY (KAFO) in the club Archer. The direct route is already problematical, but the airways route is twice as long. Sorry, not for a fun flight. A big chunk of the route has a 15,000' MSL MEA, pushing the Archer's service ceiling. And I'm not equipped for the approach. Filing IFR is not an option.

But neither is flying NoSAR, and my friend was pleased to see me file a VFR flight plan.

I tell everyone who might listen that opening a VFR flight plan is easy, and that every VFR flight allows for 2+n PIREPs, where n is the length of the flight in hours: one on departure conditions when you open, one on arrival conditions when you close, and one when you do your hourly position report. Many people no longer need to talk to FSS to get weather updates, but that position report could make big difference in your rescue.

in this case LockMart couldn't follow my PIREP on the departure conditions ("continuous light turbulence SFC-070, type is P28A, unlimited visibility"), and it took almost 5 minutes to open the flight plan.

But still I'm glad I did.

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