Page:CAB Accident Report, Pennsylvania Central Airlines Flight 19.pdf/77

 persons virtually impossible on the airplane under consideration. While the electrical effect of lightning frequently produces a magnetic field which may temporarily or permanently influence metal parts, compasses, or other instruments, there is no record of serious results therefrom on aircraft in flight.

The electrical effect of lightning has been known to produce a sudden and tremendously increased noise or vibration in the receiving unit of telephones or radios of such intensity as to produce acoustical shock, especially under circumstances where earphones are held closely to both ears. In such an event, characteristic marks are usually left upon the diaphram of the receiving unit. Although the earphones of the plane were not recovered for examination, the testimony of experts indicated that an electrical charge sufficient to produce acoustical shock upon the pilot probably would not reach the earphones due to the design and installation of the radio system in the airplane involved in the accident.

There is no reason to believe that any electrical effect of lightning other than accoustical shock may have been even a contributing cause of the accident.

The optical effect of lightning, or of any sudden and bright light, is well known. Mrs. Everhart testified, that the lightning flash which occurred in the vicinity of the airplane while she was watching from a distance of about 1½ miles was so brilliant that she was blinded for a brief time during which she lost sight of the airplane. Experts testified that the nature of lightning illumination was especially injurious to human eyesight and a considerable number of pilots have reported temporary impairment to their eyesight from lightning flashes near their aircraft while in flight for varying lengths of time depending upon such conditions as the brilliance of the flash, whether the pilot was looking directly at the lightning, the