Pavement engineer discusses runway capacity
I’m the engineer asked by a Douglas County commissioner in the fall of 2007 to review the airport pavement capacity studies. My engineering career includes extensive experience in the design and construction of airports and airport pavements. I accepted this assignment thinking it would be a routine review, comparing the collection of test data with FAA guidelines and determining the study followed standard statistical procedures and FAA design criteria. I was wrong. Two of the three studies were seriously flawed and concluded the airport could support wheel loading that are grossly in excess of actual pavement strength.
The first report, dated November 2000, consisted of a visual evaluation of the airport pavement. Based upon surface appearance, this first qualitative study estimated the remaining useful life of the various pavement features before they require repair or replacement, assuming continued use by light weight aircraft. The second and third studies used indirect nondestructive testing to obtain a quantitative evaluation of pavement condition. The limited number of data collection points used in the studies allows for the evaluation of pavement performance in terms of scheduled maintenance and or repair, but not airport pavement capacity. In addition to this procedural mistake, the strength estimated from some of the indirect testing was excessively high.
The final and most extreme flaw in both the 2002 and 2005 studies (conducted by the same firm), was the selection of representative strengths for pavement features that would result in about 60 percent of the tested areas falling below the assigned value. Most highway departments specify no more than 20 percent of tested areas fall below the assigned strength.
The FAA has an even more restrictive requirement, limiting the potential failure areas to 15 percent of the assigned value. If the FAA guidelines had been followed, the 2002 and 2005 studies would have concluded the existing airport pavement could support only a very limited number of annual departures of a 50,000 pound dual-wheeled aircraft. This is the design criterion that has been used on the airport for maintenance and repair for at least the last 15 years.
My surprise findings were summarized in a report distributed to each of the county commissioners, the acting county manager, the airport manager, the airport advisory committee and the officers of the Carson Valley Vanguard Coalition.
Apparently my findings did not fit the county’s plan for airport expansion because my report was not well received, nor ever forwarded to the FAA. Because of the flawed 2002 and 2005 pavement studies, which reported a pavement capacity of 110,000 pounds, the FAA issued the infamous letter telling the county its ordinance limiting aircraft to 50,000 pounds was discriminatory.
Early this past summer, about 30 plus months after my report was submitted to the County, Mr. Jon Hannan sent a copy of my report and photographs of Taxiway “A” to the FAA. As a result of this submittal, I received a call from the FAA informing me they agreed with my criticism of the pavement studies and my conclusions regarding the grossly overstated capacity of the airport pavement. Several weeks later I received a second phone call from an FAA pavement engineering specialist giving me a “heads up.” He notified the airport manager the 2002 and 2005 pavement studies were not acceptable and that he had requested FAA funding of $100,000 should the county wish to conduct another study. This notification by the FAA has never been acknowledged by the county or the airport administration.
Now to the proposed ordinance. I have no stake in airport development. I am not a glider pilot, I don’t mind aircraft noise and I flew with the heavy commercial airplanes out of San Jose International Airport for 28 years. As written, the new ordinance propounds to give control of any airport expansion and development to the citizens of the county. If they so wish they can retain the airport as a small general aviation center and rural setting, and also keep and/or expand the airport as an international center for gliders. A careful reading of the ordinance exposes a clever deception to this false concept of citizen control.
Airport capacity, in terms of aircraft weight, is governed by the pavement on major aprons and taxiways, not the runways. Runway pavement should be the thinnest on an airport. At the Minden-Tahoe Airport, Runway 16-34 has the thickest pavement. It appears that past airport management has clandestinely increased the strength of the runway under the guise of repair. This strengthening of the main runway in violation of the existing county ordinance is borne out by repair records as well as a report from a consultant that has worked on the airport. His client was told the airport pavement was being upgraded and could support heavier aircraft.
The fatal flaw in the proposed ordinance, as written, is the authority given to the county to increase the supporting capacity of taxiways and aprons to match that of the stronger Runway 16-34. This upgrading can be accomplished without permission, review or oversight from the community. I understand the FAA is ready to fund such paving projects should the county make such requests.
Even though the county has never acknowledged my review work, the insertion of this clause in the ordinance is evidence of their true understanding of the pavement issue. With this short clause the apparent past wishes of county voters can be sidestepped. Pavement capacity can be increased to allow for frequent use of large jet traffic, which if it occurs, will mean the displacement of sail planes from the airport. Heavy jet traffic and gliders cannot share the same airspace.
If you wish to limit jet traffic in the Valley and keep and or expand glider activity, vote against the ordinance until the offending pavement clause has been deleted.
It is truly unfortunate that our county government withholds information, and endeavors to confuse and distort issues regarding our airport. How big and for what use do the county voters wish for the Minden-Tahoe Airport?
Wayne E. Ferree is a north Carson Valley resident.