The Times’ Methodology

This is how The Times:

Calculated Fleet Age

From a Boeing publication entitled “World Jet Airplane Inventory,” ages of individual aircraft were computed based on the year they went into U.S. commercial service. Aircraft that were sold abroad or imported from abroad were also taken into account.

Compiled Service Difficulty Reports and Airworthiness Directives

All SDRs filed with the FAA’s Safety Data Branch over five years were obtained. The SDRs were from 1980 through 1984, which included years during which the effects of deregulation might be expected to become evident. Last year was excluded because some SDRs were still in “open” status while others were missing because of lag time required by FAA processing.

Within those five years, SDRs on the six preponderant types of aircraft were isolated. A compilation was made of those reporting defects in what the Air Transport Assn. defines as structural components. These components included parts of the airplanes, such as fuselages, pylons, wings and tails. By computer, The Times counted the structural SDRs filed during each of the five years for each of these six aircraft types.

Computed Maintenance Spending

Financial reports for 1980 through 1984, filed by the airlines with the Department of Transportation, were obtained from I. P. Sharp Associates, a firm that provides computerized data from government and industry. Sharp singled out airline spending for all structural maintenance on the six preponderant aircraft in the fleet. The expenditures included labor and materials for structural inspections and repairs performed by airlines themselves or outside service stations under contract to the airlines.

With guidance from the American Institute of Certified Public Accountants, The Times calculated yearly totals for each of the six aircraft. It applied bookkeeping methods used by the airlines to account for structural maintenance based on cash spending as well as on amortizations and deferrals. Each calculation was adjusted for inflation by using the consumer price index, the most conservative approach to indexing. Wages for airline mechanics, a substantial portion of maintenance costs, increased faster than the CPI between 1980 and 1984, according to Department of Labor wage surveys.

These experts were retained by The Times for technical assistance:

Jerry J. Presba, aeronautical engineer; FAA designated airworthiness representative; retired FAA technical support chief and regional service difficulty coordinator.

Isaac H. Hoover, airlines structures engineer; FAA designated engineering representative; retired FAA deputy regional director and program manager for airframe safety research and development.

James M. Dimin, retired airline manager of fleet reliability and power-plant engineering; former engineering specialist and design specialist.