AVmail: October 29, 2009

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Each week, we run a sampling of the letters received to our editorial inbox here in AVmail. One letter that's particularly relevant, informative, or otherwise compelling will headline this section as our "Letter of the Week," and we'll send the author an official AVweb baseball cap as a "thank you" for interacting with us (and the rest of our readership). Send us your comments and questions using this form. Please include your mailing address in your e-mail (just in case your letter is our "Letter of the Week"); by the same token, please let us know if your message is not intended for publication.

Letter of the Week: Safety or Punishment?

Yes, the pilots of NW 188 made a mistake. However, it is a shame that we are so focused on blame and punishment. What ever happened to "learning from our mistakes"? Given their experience (and especially their most recent experience) and previous records, I can think of no other flight crew I would rather have in the cockpit the next time I fly.

I know they would be on top of their game because they know it can happen to them. But, no, I'll be riding with a low time, marginally qualified crew who may have never seen ice and doesn't know what to do if it is encountered, or a crew that can't tell they are lined up on the wrong runway, while these two highly experienced pilots are looking for a new career. Is it about safety or about punishment?

Jim Oeffinger

I had to chuckle when I read this article. Seems like there was a similar incident out in Hawaii a few months ago.

Back in 2003 we added a feature to our autopilots that recognizes the last waypoint in a flight plan and will cause the airplane to circle that last waypoint if this feature is enabled. We did this because we had a couple customers in a short timeframe pass their last waypoint and didn't become aware of it until sometime down the road. Not sure if they winked off but they sure did like it when we added the feature. I cannot recall if they worked for NWA.

Chuck Busch
President, Trio Avionics

Drop-In Maintenance?

Cessna may run afoul of airport regulations regarding commercial maintenance with its ServiceDirect Program. Virtually all airports have some form of restrictions on outside service providers. Permission must be granted by the airport manager for a through-the-fence service. Any maintenance performed inside an airport boundary must conform to the local rules. Most of those rules require a lease, a fixed place of business on the field, and local or state registration of the business enterprise.

When Cessna comes calling at my local airport they will be turned away until they gain approval from the airport manager. That is no easy task, in light of the rules, which are designed to keep out moonlighters and to fill the local tax coffers. Cessna may circumvent the rules by contracting through established FBO's, but how many are going to give up their prime customers that way?

Glenn Juber

Balloon Boy Math

I would like to raise one point about such calculation that your story doesn't cover - the profound effect of scaling on balloon lift.

A difference of plus or minus 10% in the scale of a balloon yields a near doubling of its gross lift. (For balloons, gross lift goes as the cube of scale.) Thus, the 65 lbs of gross lift calculated for your story, could have been anywhere from 47 to 87 lbs with only a 10% error in estimation of scale. That difference in gross lift makes all the difference in the world when trying to make a first-order plausibility assessment.

I am acutely aware of this particular scaling issue because during the time that the balloon was aloft, I and several of my fellow balloon builders were contacted by members of the press. Each of us considered the gross lift question at the time. Given what we know about balloon construction, we were deeply skeptical of the idea that the balloon on our TV screens could lift a six-year-old. Although we all very much wanted to allay public fears at the time, we found it impossible to make a full-throated hoax/no-hoax call before the balloon had landed and before the launch video and other size-related hints were available. And the thing holding us back was the effect of scale described above.

Dan Nachbar

I'm glad to see someone finally did some math. (I did, but I heard about it well after the fact) If someone had done it in the first place we could have avoided all the fuss, drama, and charges other than possibly shutting down DIA. (Seems someone else in a balloon shut down LAX and suffered some penalties.)

A quick calulation would have saved a lot of unnecessary emergency activity. Anything you needed to calculate the lift of a balloon is readily available on the internet except for the ability to estimate the volume which is actually less since it was not cake shaped. The lift at 5,000 feet should have been enough to eliminate the chance that the boy was on board and the lack of deformation of the gondola should have been another.

I'm glad you pointed it out, and I hope someone is listening.

G. Walters

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