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COLONIAL AIRLINES, INC

TO: ALL PILOTS

FROM: Director of Flight Operations

SUBJECT: Summary of Notice to Pilots - Jan 29 1951

USE OF FULL TAKE-OFF POWER. (MBW 1-29-51)
A lively argument can always be started as to whether or not engine durability is increased by using reduced power during take-off when conditions do not require the full rating. The Manual of Engine Operation on page 97 has given aid to those who feel that "easing off" is best. This letter is being written to withdraw this support and place Pratt & Whitney Aircraft's printed word on the side of those who would use the full rating regardless of load or runway length Any aircraft engine, to obtain certification must amply prove its ability to withstand the loads resulting from applying take-off power. The CAA type test requires 10 hours continuous operation at this output; the equivalent of over 1000 take-offs. There need be no thought that the engine is close to the brink of destruction at this time. Airplane-wise, reduced power would seem to be the equivalent of starting one third down the runway. While it is not the function of this letter to suggest methods of airplane handling it would seem best to reach one-engine-out safety speed as soon as possible.
Engine-wise, there is very little to recommend in support of reduced power. The only load reductions are the pressure loads imposed in the combustion chambers and the difference would not affect engine life. The same pressure loads oppose the rpm produced loads on the reciprocating system because pressure cusions the centrifugal and inertia forces. If the pressure load is reduced, the wear due to high rmp is increased. This factor is further accentuated by the increased time required to reach the rpm reduction point. Sustained high rmp is a major factor in keeping engines from staying young and it takes more "rmp minutes" and "piston ring miles" along the cylinder walls to complete the first rake-off phase if the manifold pressure is reduced. It is also advantageous to reach an airspeed that provides cooling airflow as soon as possible.
If detonation is the fear, consider that reduced manifold pressure means less induction airflow which in turn means a leaner mixture. As the impeller speed remains the same, the mixture temperature is still at its maximum and the slight help from lowered pressure is offset by the leaner mixture. The mixture temperature factor is of major magnitude and a theoretical case could be made for reduced power with tropical temperatures (120 F plus) provided that rpm as well as manifold pressure is lowered. Less rpm means lower supercharger temperature rise which, detonation wise, would offset the leaner mixture resulting from the diminished airflow. Data from closely controlled detonation runs show that if rpm and manifold pressure are reduced together the maximum safe power will be greater under extreme conditions than that permissible with solo reduction of manifold pressure. However, as propeller efficiency is adversely affected, it is not possible to make any specific recommendation in this regard and this procedure should never be attempted without sufficient data to insure that all necessary margins are covered.

VAR RANGE. (MBW 1-29-51)
Some of the pilots seem a little vague as to how VAR ranges operate. For your information, here are a few points to be remembered:
1. There is no cone of silence, this is replaced by a cone of noise. 
2. Because of the automatic volume control in the receiver, we do not get a fade as we get further away from the station; instead, we get an increase of noise.
3. The aural course is about 2° instead of 3° as in the case of LF ranges.