526 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



conditions and of the transmission and reception of such intelligence 

 to such degree as shall serve for a reasonably adequate determination 

 of the quality of the weather over any proposed route with reference 

 to this standard; and if, over the proposed route, the weather falls 

 outside this characterization, the flight should be canceled. 



Now from the viewpoint of the plane and its services, in what way 

 may accidents arise? Without attempting too much detail, we may 

 say that accidents find their causes chiefly in — 



1. Faulty aerodynamic characteristics. 



2. Failure of the structure. 



3. Failure of motive power. 



4. Failure of, or inadequate, navigational equipment. 



5. Inadequate or erroneous information received from the services on the 



ground. 



6. Human errors. 



Again with regard to weather conditions, those which present 

 major hazards are : 



1. Rain, snow, and fog, especially the two latter in degree requiring blind 

 flying. 

 • 2. Violent winds, air vortices, extreme turbulence. 



3. Temperatures below freezing under atmospheric conditions which may 



involve the loading of the plane with ice or frozen snow. 



4. The electrical state of the air — not primarily with reference to the hazard 



of a lightning stroke, but chiefly by reason of the interference with the 

 services of radio communication. 



A brief word with reference to these sources of potential hazard. 



With our present knowledge of the aerodynamic characteristics re- 

 quired for safety and with the intensive study which is being given to 

 refinements in these matters, we may, I think, feel confident that 

 present design is, and future design will be, free of fault in its 

 aerodynamic characteristics in any degree likely, with proper hand- 

 ling, to involve a major hazard in service. 



With regard to the structure of the airplane, I think we may also 

 say that the problems involved in the design and construction of the 

 major parts of an airplane structure are now so well in hand that, 

 in commercial service especially, major structural failures should 

 become almost unknown. In this particular we may claim close 

 approach to an entirely reassuring condition — a condition indicated 

 by the rarity, in recent years, of accidents resulting from major 

 failures of the structure of the plane itself. 



Failure of the motive power, including engine and propeller, may 

 have its source either in the structural elements themselves (for 

 example a broken crankshaft or propeller blade), the exhaustion of 

 the fuel supply, or in stoppage due to disturbance in the somewhat 

 delicate conditions involved in carburetion and ignition, or, again, 

 in failure in the adequate lubrication of all rubbing surfaces. 



