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COLONIAL AIRLINES, INC. January 12, 1949 All Pilots G.R. Janas [[Underlined]] DC-3 Heater Operation Supplementary to he comments which were recently issued concerning the operation of the DC-3 heaters, the Maintenance Dept. suggested that we bring the following items to your attention in regard to dropping the water from the expansion tank. Even though the boilers have been primed and the water has not yet been dropped, the initial pressure indication on the expansion tank gauge is usually that of air pressure only, which is caused by the expansion of steam in the system and the inability of the air relief valve to discharge the air rapidly enough. Thus it is possible to have pressure on the gauge and yet have the heating system cold. If the water is dropped under these conditions it is possible that it will freeze in the plumbing immediately below the expansion tank. It is therefore requested that the pilots open the manual drain and air vent valve and wait until steam issues therefrom before dropping the water. G.R. Janas GRJ: gmo cc:B.T. Dykes C.F. Watts T. Volz