It was 1:30 am on November 4, 1957 that Chief Pilot Captain Jean Vincent de Beyssac and his co-pilot were flying from Porto Alegre to Sao Paulo, Brazil, a distance of approximately 550 miles to the NNE. After about an hour they were near the town of Ararangua with some 400 miles to go. Their most likely flight path was along the coast of the Atlantic where automobile and town lights could help in their nighttime navigation. Their airplane was a two engine, propellor-driven, C-46 cargo airplane operated by Varig Airlines.
Flying above an undercast at about 2,300 m (approx.) 7,000 feet AGL the captain first noticed a red light at an unknown distance on their left side and at a lower altitude. He instructed his co-pilot to get out of his seat and come look at it. The apparent shape of the UAP wasn't indicated but it seemed to be enlarging so Capt. de Beyssac began to bank left in its direction (apparently) out of curiosity. As he did the light suddenly "...leapt through an arc of about 45 degrees and appeared much larger in size. He felt that the light was approaching them. Its direction of travel was not specified but is assumed to have moved generally toward the NE along with the airplane. He continued his left turn, passing through a 40 degree heading change. Then the UAP began to "...glow more brilliantly" and the crew smelled smoke in the cabin. (No fire alarms went off). While the pilots were diverted trying to locate the source of the smoke the UAP faded from sight. Later it was discovered that the right engine's magneto (or generator?), Automatic Direction Finder (ADF), and the radio (both receiver and transmitter) had burnt out, allegedly simultaneously. Capt. de Beyssac immediately: (1) reported the incident to ATC at Porto Alegre, (2) activated his emergency locator transmitter (perhaps expecting further problems), and (3) reversed directions and returned to his departure airport an hour later.
Note: A NARCAP Research Associate in Brazil who flew with Captain de Beyssac (Varig, B-707) wrote me recently (May 2009) that the witness is now over eighty years old and lives in Porto Alegre.The NARCAP correspondent said that he had also corresponded with son Luiz de Beyssac in 2009 seeking further details. He sent the enclosed photo.
As you know, this aerial encounter was written up by a number of authors over the years. Also see http://www.ufologie.net/htm/varig57.htm
A powerful electro-magnetic surge could produce the effects reported but would certainly open circuit breakers in the process.
Hope this helps,