Posted by: harrisonjones | July 16, 2011

Faith in the yellow line

Pilots all know that  taxiways have a nice yellow line painted down the center and one would assume  that certain guarantees are implied by adhering to the yellow line. That would  be a dangerous assumption. When you taxi with the nose wheel on the yellow  line, the only guarantee is that the nose wheel is on the yellow line and if  the taxiway has centerline lights embedded, you will hear the thump-thump-thump  that tells you to move over a foot so the passengers won’t think you have a  flat tire.

As you can see, the RJ above has had its tail feathers ruffled by the wingtip of a 767. I have no  idea how that occurred or who might have erred, but they were probably both on  the yellow line. It’s important to know where the nose wheel is, but a bigger  concern is the wingtips, the main gear, the engines, and the tail. Let’s face  it; the size of airplanes has increased much faster than the width of taxiways  over the years. 

The visibility from  the cockpit of a transport aircraft is much more restricted than most would  think. To give you some perspective, I’ll use the MD-11 as an example.

As you can see, the pilot is 20 feet above the ground and the first visible pavement is 55 feet  away. The side windows of the cockpit are in the pointy end of the airplane and  actually slant forward slightly. You cannot see the engines or the wingtips.  The tail is 200 feet away. One advantage is that the nose wheel is mounted 21  feet behind the pilot, thereby reducing the overall wheelbase and allowing  tighter turns. This requires allowing the cockpit to go far beyond the yellow  turn line before turning. Many times the cockpit is beyond the pavement before  turning and that is referred to as the a** over the grass maneuver. Sorry, it’s  true. These are the measures you must take to insure that the main gear, 123  feet behind you, stays on the pavement throughout the turn. The yellow line  becomes a moot point. The wingtip is farther away from the main gear than the nose,  which means that if the nose clears an obstacle (jetway, truck, another  airplane) it doesn’t guarantee that the wingtip will. The good news is; if the  wingtip clears the tail will too. Taxi can be a challenge and I’m not talking  about Macon, Georgia. New York, Boston and Los Angeles have some tight spots  also. Add a little snow and ice and the fun is almost too much. Here’s one more  perspective.

A normal touchdown  places the pilot 40 feet in the air with a blind spot of 186 feet directly in  front. We’re just looking at a small corner of the big picture, but I hope it  provides some measure of insight. The yellow line is just one of many and we’ve  all heard the motto, “In God we trust; everybody else gets a check ride.”

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