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Wednesday, Oct 8, 2008
Exploding tires and bad math; the pilot exposes his darkest secrets.
Oct 14, 2005 | Here's a letter:
"Patrick Smith, your credibility as a commentator on all things aviation-related would be more sustainable if you'd get the physics right. Your reference to a 'forward-acting force against your body when applying the brakes in your car,' being akin to the force that brings down the nose of a landing plane, is complete hogwash.
"First, there is no forward-acting force when braking in the car. Your inertia keeps you moving forward, but the force you feel is a reverse-acting force exerted by whatever part of the car you're in contact with (safety belt, most likely), to keep that inertia from sending you into the windshield. More importantly, this is only indirectly related to the lowering of an aircraft's nose after touchdown. Two things bring the nose down: the force of gravity pulling the front of the plane toward the earth, and torque rotating the aircraft around the rear wheels, caused by application of the brakes. The reason for the JetBlue pilots not to brake heavily was to allow forward speed to bleed off slowly, thus allowing residual lift on the nose, and torque tending to rotate the nose upwards (generated by air acting on the wings and horizontal stabilizers), to yield to gravity as gradually as possible."
You mean that's not what I said? The above scold (I cleaned and paraphrased it slightly), comes from Steve Demuth of Decorah, Iowa, calling me out for my description of why the pilots of JetBlue 292 -- the too-famous Airbus with the crooked front tires -- were obliged to take it easy on braking and reverse thrust upon landing at LAX. Letting the nose fall gently was, Demuth explains, all about torque and gravity. Everybody clear?
With respect to the inertia thing, indeed the force a driver feels when jamming on the brakes is technically a backwards-acting force, but describing it as such would have thrown readers off. You perceive yourself being hurled forward. One option to "forward-acting force" was to type "forward-feeling force" -- a phrase of such alliterative horror that I went ahead with the lie.
Besides, what do you expect from a math and physics flunky? It's funny, because I often get letters from aspiring pilots-to-be worried that below-average mathematics skills might keep them grounded. There's a lingering assumption that airline pilots are required to demonstrate some sort of Newtonian genius before every takeoff -- a vestige, maybe, from the days when airmen carried slide rules and practiced celestial navigation. Dear Patrick, I'm a high school junior who hopes to become a pilot, but my C-minus in honors-level pre-calculus has me worried. What should I do?
What these people don't realize is that I would have killed for a C-minus in elementary algebra. (My final semester report card from St. John's Prep, class of 1984, reads something like this: B, B, C, D, D, C.) I can only vaguely define what pre-calculus might be, and I frequently struggle to make change for a dollar or add up my Boggle scores without use of a calculator. In spite of this, I never graded lower than a 97 percent on any FAA written exam, and no fewer than four airlines considered me worthy of wearing four stripes (before going out of business or laying me off, but still). My logbook records no math-related incidents or catastrophes.
Not that I couldn't use some tutelage with the basics -- and basics are what pilots encounter. At my last job, for example, routine arrival assignments demanded some quickie mental arithmetic. Modern flight-management systems will hash out descent profiles automatically, but on the classic model 737 we had to run the data in our brains: "OK, if we need to be at 14,000 feet in 60 miles, assuming a 2,000 foot-per-minute descent and 320 knots groundspeed, at what point should we start down?" Like an SAT question, but with hundreds of passengers assuming you're smart enough to know the answer. Not to mention an ornery captain, who'd eye me suspiciously as I reached for the old Texas Instruments. "What, you can't figure that out?"
"Sure I can. I'm just more comfortable this way."
Flying as the second officer on old cargo jets, my duties included the ciphering of weight-and-balance figures and the en route management of fuel (in addition to the more important duties of serving dinner and emptying the trash). On a flight from the United States to Europe, our total weight approached half a million pounds, with tens of thousands of pounds of kerosene to balance among eight tanks. In other words, there were lots of numbers. They didn't require anything too elaborate -- I'd add them, subtract them, portion them in half or a quarter -- but they were big, six-digit affairs that were constantly changing.
With that in mind, look closely at this photograph (snapped early one morning before takeoff for Brussels, Belgium) of the second-officer workstation of the DC-8-73F and try to pick out the most critical cockpit instrument of all. Hint: It was not furnished by the designers at Douglas, who conceived this hideous ark of a plane back in the mid-1950s, when men were men and could fly and do long division at the same time. I'm referring to my $6.95 calculator from CVS -- the one flight bag accessory more indispensable than an emergency checklist, aircraft de-icing guide or bag of ramen noodles. You can see it on the lower shelf, just to the right of my plastic flashlight, marked by a Day-Glo orange sticker affixed in mortal fear that I might otherwise leave it behind.
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