AVmail: Feb. 6, 2006

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Reader mail this week about user fees, thrust reversers, wake turbulence and more.


User Fees

We have user fees: Gas tax provides millions based on usage (NewsWire, Jan. 30); meanwhile they squander ... $75 million on questionable rehab at MKC. Plenty of money; let's have some accountability instead of having a tax on a tax.

John Grissinger


Retired at 32?

It's a little unusual to be a "retired" Marine at age 32, but not impossible, I guess (NewsWire, Jan. 30). Generally, Armed Forces retirees have served at least 20 years before full retirement, unless they retired for medical reasons, I believe.

Frank Radspinner


Thrust Reverse for Stopping

I have been flying FAR Part 135 for more than 25 years and have always been taught (and teach) that it has always been the FAA's policy to never allow thrust reverse (prop or jet) for computing landing distance. I was amazed to read your article on this subject (NewsWire, Jan. 30). If you check into the matter I believe you will find this is a fact, but like any other situation, if your company has enough "clout" then they will look the other way while you go about doing your thing and getting help from a government agency to have a leg up on your competition. If I can't land using this equation why can the major air carriers?

Bill Maynard

AVweb Replies:

Here is what the NTSB said in regards to the rules on those calculations:

"The FAA does not allow the use of the reverse thrust credit when determining dispatch landing distances; in fact, historically decreases in stopping distances due to thrust reverser deployment were used to offset other variables that could significantly degrade stopping performance. However, the FAA does permit thrust reverser credit for calculating en-route operational landing distances for some transport category aircraft, like the 737-700 series, but not for others, like the 737-300."

I hope that clarifies it for you.

Mary Grady
NewsWriter/Editor


An Old Timer's Observations On Wake Turbulence

I recently moved to a house about two miles out on the centre line for Liverpool airport and was fascinated by the ripping noise that occurs about two miles behind approaching aircraft, which you seem to call wake turbulence! What fascinated me so much was that in my youth I flew Gloucester Javelins, and in 10 years on RAF airfields I never heard it -- not behind fighters, not behind VC10s, not even behind the Vulcan bomber. The riddle was soon solved by observation. The phenomenon does not occur behind turboprops. Nor does it occur behind the few airliners left with turbine jets. It only occurs behind bypass (fan) jet engines.

Now I'm no gas expert, so I can't tell you exactly what's happening but it would seem to me that the exhaust gasses from a fan jet are somehow "cocooned" by the tube of cold air from the fan and the violent mixing of hot and cold that occurs immediately behind the jet pipe of a turbine does not occur behind a fan jet 'till this cocoon breaks down about two miles behind.

All the literature I've seen on wake turbulence simply refers to the wingtip vortex effect. That's real enough but I've been in it lots of times and it doesn't break aeroplanes. What happens two miles behind a fanjet does, because being there is like being 10 feet behind a turbine.

John Turnbull


Inequitable Fines

In reading your article, "FAA Suggests $840,000" (NewsWire, Feb. 2), it amazed me the difference between this number [for Cessna's fine] and what the coal industry is paying for fines for safety violations that endanger thousands of miners. The fines the coal industry is paying are below $500 in most cases. I guess GA is not on the favored list of industries that this administration wants to support.

Larry McCormick


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