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COLONIAL AIRLINES, INC.
MAINTENANCE DEPARTMENT

S.L.# 166
1/17/49

To: All Maintenance Personnel
From: Director of Maintenance 7 Overhaul
Subject: Freezing of DC-3 Steam Heating System

Recent instances of freezing of steam heating system have resulted in pre-departure delays. That such delays may be avoided in the future, your attention is directed to the instructions contained in this letter. 

Prior to taxiing the airplane to the gate, carefully follow this procedure for servicing of the heating system.

1. Prims boiler with two quarts of hot water just before starting right engine.
2. Close shut-off valve at the bottom of the expansion tank, and pour four quarts of hot water into tank.
3. Close expansion tank filler neck valve.
4. Open by-pass valve and close pressure line shut-off valve.
5. Close nose valve and check that main steam valve is "on".
6. Do not open expansion tank shut-off valve until the following checks have been made.
   1. After first indication of pressure on steam gage, open manual bleed valve ("G") and leave open until steam is being discharged from the bleed line.
   2. Close normal bleed valve and check steam pressure.
   3. When steam pressure is 15-20 psi, open expansion tank shut-off valve and release water trapped in expansion tank.

Caution: Heating systems have been frozen as a result of premature release of water trapped in the expansion tank. This water then became frozen in cold lines. First indications of pressure on the gage may be false, and due to improper venting of air trapped in the system. System must be bled manually until live steam escapes through the blood line. This is an indication that system is functioning properly. Following this step, a stable gage pressure of 15-20 psi, is a reliable indication that water trapped in the expansion tank may be safely released into the heating system. 

Chas. F. Watts.