Philip Greenspun’s Weblog

The recent mid-air collision in Brazil of a new regional airliner (fitted out for use as a business jet) and a Boeing 737 has people baffled. How could two brand-new airplanes with advanced avionics, flown by two professional pilots in each plane, collide at 37,000′? The precision of modern avionics may well have contributed to this collision.

Airplanes under instrument flight rules fly from one navigation beacon to another along published standard routes. In the old days, with radio navigation receivers and pilots flying by hand, a plane wouldn’t fly its clearance exactly. The airways include a tolerance for error of +/- 4 miles. If you’re 4 miles to the right of course, in other words, you’re still legal and safe from hitting mountains or other obstacles. Altitude was similarly sloppy. If you reached for a drink of coffee or to look at a chart, you might drift up or down 200′. Air traffic control wouldn’t get upset.

How does it work now that the computer age has finally reached aviation? The GPS receiver computes an exact great circle route from navaid to navaid. All GPS receivers run from the same database of latitude/longitude coordinates, so they all have the same idea of where the Manchester, New Hampshire VOR is, for example. The autopilot in the plane will hold the airplane to within about 30′ of the centerline of the airway and to perhaps 20′ in altitude. If two planes in opposite directions are mistakenly cleared to fly on the same airway at the same altitude, a collision now becomes inevitable.

Almost any other system would be safer. If you sent airplanes up to fly in random point-to-point paths, e.g., from Boston to Denver, they’d be less likely to encounter one another. If you kept the airway system, but introduced some extra logic into the avionics so that planes always flew 1 mile to the right of an airway and + or – 200′ in altitude, they’d be less likely to encounter one another. If you replaced the precise autopilots with imprecise humans, planes would be less likely to encounter one another. If you replaced the high-precision GPS receivers with low-precision VOR receivers, planes would be less likely to encounter one another.

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I was giving a lift to one of my helicopter students from the military side of Hanscom Field back to the civilian parking lot. “I’m driving my [18-year-old] son’s car today,” he noted. I scanned the parking lot for a 1998 Honda Accord or similar. He directed me towards an almost new black Mercedes E-series sedan, the $50,000+ dream car of so many yuppies. “I like all of the airbags,” my friend said. “He’s already had five accidents.” Was it a car that this health care professional had bought for himself and then given to the kid? “Oh no. I was born to be a father and I just love giving things to my kids.”

Christian Europeans at various points in history passed anti-finery laws prohibiting Jews from wearing fancy clothing or jewelry. This incident led me to wonder if we shouldn’t have a similar law for teenagers. We want Americans to work hard and strive to improve their salaries so that they can grow the economy and pay more taxes. If a guy who is working two jobs to improve his economic situation sees a kid driving to high-school in his own brand-new Mercedes merely in virtue of having been born into the family of a doctor/dentist/lawyer/whatever, might it not demotivate him a bit?

Perhaps I have gotten out of touch with the modern world. When I attended public high school in Bethesda, Maryland in the late 1970s, a rich kid was one who had a car of any kind. Has it all escalated to the point where in suburban Boston a kid needs a new Mercedes to hold his head up among his peers?

[Or maybe I’m just envious, driving a 1998 Toyota minivan that smells like a wet dog.]

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Yesterday’s mail contained a newsletter to neighbors (Cambridge, MA residents) from Harvard University. It was just after I read a news report on Harvard’s endowment, which earned 16.7 percent on an approximately $30 billion stash. In other words, Harvard earned around $4.5 billion, tax-free. After deducting for inflation, in other words, Harvard earned enough last year to purchase a nuclear-powered aircraft carrier, complete with a fleet of fighter jets. What did the letter to neighbors say? It seems that one day per year, Harvard’s museums, normally $10 per person per museum, open their doors to Cambridge residents for free. That’s right, 1/365th of the time, Harvard will not collect every last possible dime. When is this glorious day to occur? September 17, 2006. I.e., the “connections” newsletter arrived in my mailbox several days after it would have been possible to visit the museums for free.

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For those who believe that aviation and alcohol don’t mix well, a video of Robinson R22 and R44 helicopters being used to open beer bottles… http://www.glumbert.com/media/beerbottle

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Our summer rental in Lincoln, Massachusetts, a Boston suburb with two-acre minimum zoning, is coming to an end. My friend Tom asked me whether I was sorry to be giving up the yard, woods, and pond and moving back to my crummy two-bedroom apartment in Harvard Square. I said, “Well, in three months here I’ve only met one other person.” Tom said that he’d lived in a Manhattan high-rise and found it difficult to meet people outside of work. The authors of A Pattern Language advocated a three- or four-story maximum height for housing with a lot of public squares, which is sort of what Cambridge is like (sadly the three- and four-story structures are wooden and fell into disrepair 50+ years ago). It is definitely much easier to meet folks while out walking the dog in Cambridge than wandering around in isolation over the trails of Lincoln.

Could it be that Cambridge has the ideal physical structure?

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One of my favorite things about God is that He chose to give most of the world’s money to folks who aren’t sure what to do with it. Some friends of mine want to start and run an online community sort of like www.photo.net, but on a different topic. Have you ever asked yourself “I wish there were a photo.net for ____”? If so, on what topic(s)? Please use the comment section to answer.

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We gave at least 30 MIT students rides on Labor Day. An interested photo is on the front page of the September 8, 2006 Tech. The fly-in inspired me to write http://philip.greenspun.com/flying/helicopter-landing-zone

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A friend of mine recently went to work for a 50-year-old 200-employee company that has bumbled along with modest success as a niche supplier in its (very large) market. She talked about how happy the employees were and how so many had worked there for decades. I said “That means they are overpaid.” She questioned me on this point. I cited a study of married people that found that each thought he or she was doing more than 50% of the chores. The explanation was that a husband is guaranteed to be watching when he himself is doing a chore, but doesn’t see all of the things that the wife is doing (and vice versa). The same phenomenon applies at work. An employee knows all of the things that he or she does personally. The employee isn’t aware of what the others in the company are doing. Consequently, the employee develops a major overestimate of his or her relative productivity and the percentage of overall work done. (Programmers, starting off with massive egos and having little contact with other human beings, are perhaps the worst overestimators of all, especially the 80% of programmers whose contributions are purely negative.)

An employee will overestimate his value to the company by at least a factor of 2. If he is not griping about his salary, it means you’re paying him at least twice as much as he is worth.

[Shortly after this conversation, the investor who had recently purchased the enterprise decided to fire the long-serving Chief Operating Officer.]

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The weather forecast calls for clearing conditions here in Boston. If you’re around and want to go for a helicopter ride, come to Briggs Field at MIT (the end closer to the BU Bridge) between 10:30 and 1 tomorrow (Monday, September 4) and you can buy a raffle ticket for $5 that will probably get you on or just wave some serious cash and the students running the show will let you ride. The whole thing is a benefit for the MIT Flying Club and their Web page explains more about the event. All proceeds go to the club; I am paying for the machine and the gas.

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Yesterday’s airliner crash in Lexington, Kentucky has resulted in a few friends asking how it might have happened.

It was dark, one hour before sunrise, and hazy (see http://www.airnav.com/airport/KLEX). Runway 26 and Runway 22 start almost right next to each other (see official FAA airport diagram). The short runway, 26 (oriented in magnetic direction 260), would be reached first by an airplane taxiing from the terminal. The 3500′ of runway is very comfortable for a slow piston-powered airplane, tight for a light business jet, and more or less impossible for a fully loaded airliner.

This is not the kind of mistake that two professional pilots would be likely to make. If it hadn’t been dark and hazy, the control tower would probably have noticed the mistake and called to suggest aborting the takeoff.

How can we pilots protect against this kind of error? In airplanes with a heading bug, always set it up for runway heading before leaving the runup area. If you are positioned on a runway, preparing for takeoff, and the HSI is not lined up with the heading bug, this gives an extra opportunity to notice that something is wrong. Of course, the airline crews usually do things this way and it didn’t help the folks in Lexington.

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