57-03-03 DOUGLAS AND LOCKHEED: Applies to Lockheed Constellation Series and Douglas DC-7 Series Airplanes. \n\n\tCompliance required by April 1, 1957, for Constellation aircraft and by May 1, 1957, for DC-7 aircraft. \n\n\tUnder certain cold weather operating conditions the perforated paper covering around the Purolator micronic filter elements are subject to accumulation of ice as a result of entrained water crystals in the fuel freezing on this covering. This interferes with proper fuel filtering by causing the fuel to pass through the bypass valve in the filter unit. To make the micronic filter less susceptible to clogging by ice, the perforated paper covering around the filter element is to be removed. Removal of the perforated cover does not affect the filtering characteristics of the filter element. Filter elements without the paper covering are identified as Purolator P/N 30868-3.