The black box recovered from the wreckage of the plane crash that killed Brazilian socialist presidential candidate Eduardo Campos failed to record his flight, the air force said Friday.

The two hours of recordings it contained were not related to Wednesday's doomed flight, according to the military branch in charge of the investigation into the crash.

"The reasons why the recording does not correspond to the flight will be studied during the investigation," the air force added, noting that the voice recording was not "crucial" to the probe seeking to determine the causes of the crash.

Campos, 49, died when his campaign jet slammed into houses in Santos city in bad weather, killing all seven people on board and setting buildings alight.

He had been running third in opinion polls for the October election.

A popular former governor of the northeastern state of Pernambuco, Campos was married with five children, the youngest just six-months-old.

His remains are due to be buried in the coming days in Recife, capital of Pernambuco. An open air mass is also planned.