Section 161.013-7 - Signal requirements(a) An electric light must have a flash characteristic of the International Morse Code for S-O-S and, under design conditions,(1) Each short flash must have a duration of 1/3 second;(2) Each long flash must have a duration of 1 second;(3) The dark period between each short flash must have a duration of 1/3 second;(4) The dark period between each long flash must have a duration of 1/3 second;(5) The dark period between each letter must have a duration of 2 seconds;(6) The dark period between each S-O-S signal must have a duration of 3 seconds.
(b) The flash characteristics described in paragraph (a) must be produced automatically when the signal is activated.