234 BELL SYSTEM TECHNICAL JOURNAL 



near the Chicago airport is an excellent object upon which to demon- 

 strate the altimeter performance. The instrument is useful as a 

 position indicator when approaching an airport on a course which 

 crosses an obstruction of appreciable height and size since the mo- 

 ment of passage over the obstruction is clearly indicated. In fact, 

 use as a position indicator may be one of the altimeter's most valuable 

 applications. 



A study of the circumstances in connection with a number of 

 crashes in the west during recent years has revealed that in most of the 

 cases the airplanes crashed after having been within a few feet of the 

 ground without the pilot knowing it for several minutes before they 

 struck. In such a situation the terrain clearance indicator should be 

 capable of warning the pilot in ample time to avert a crash. 



The writers wish to express their appreciation of the contributions 

 of a number of other members of the technical staff of the Bell Tele- 

 phone Laboratories to the success of this project. 



References 



1. H. Loewy, U. S. Patent 1,492,300. 

 H. Loewy, U. S. Patent 1,585,591. 



C. F. Jenkins, U. S. Patent 1,756,462. 



E. F. W. Alexanderson, U. S. Patent 1,969,537. 



F. H. Drake, U. S. Patent 1,987,587. 



2. U. S. Patent 2,011,392 issued August, 1935 to J. O. Bentley. 



3. Page 29 of "Solving the Problem of Fog Flying," a publication of the Daniel 



Guggenheim Fund for the Promotion of Aeronautics, 1929. 



4. "Altitude Measurements by Reflected Electro-Magnetic Waves" by Murray 



Hively and R. C. Newhouse, Ohio State University Library, 1929. 



5. "An Electro-Magnetic Altimeter" by R. C. Newhouse and J. D. Corley, Ohio 



State University Library, 1930. 



6. U. S. Patent 1,517,549 issued December, 1924 to Lloyd Espenschied. 



7. U. S. Patents 2,045,071 and 2,045,072 issued June, 1936 to Lloyd Espenschied. 



8. "A Negative Grid Triode Oscillator and Amplifier for Ultra-High Frequencies," 



A. L. Samuel, Proceedings of Institute of Radio Engineers, 25, Oct. 1937 (1243). 



9. "A Research of Direct Reading Altimeter for Aeronautical Use by Radio Re- 



flection Method," Sadahiro Matsuo, Journal I. E. E. Japan, No. 571, Febru- 

 ary, 1936. 



10. "A Direct-Reading Radio-Wave-Reflection Type Absolute Altimeter for Aero- 



nautics," Sadahiro Matsuo, Proceedings of Institute of Radio Engineers, Vol. 26, 

 1938 (848). 



11. Trans. A. I. E. E. 49, 1930 (1331). 

 Proc. I. R. E. 19, 1931 (659). 



Review of Scientific Instruments 6, 2, January, 1935. 

 Journal of Scientific Instruments 14, 1937 (136). 



