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STORY: Engines from the plane that crashed in Brazil killing all 62 people on board were sent to Sao Paulo for examination, as investigators worked to establish why the aircraft fell out of the sky.

::How did the crash occur?

Here's what we know so far.

The ATR-72 turboprop passenger plane was bound for Sao Paulo from Cascavel, in the state of Parana, and crashed at around 1:30pm in the town of Vinhedo some 50 miles northwest of the city.

Brazil's air force said the aircraft operated by the airline Voepass was flying normally until 1:21 p.m., when it stopped responding to calls, and radar contact was lost at 1:22 p.m. The plane did not report any emergency.

The sky was apparently clear when the plane started spiraling in an unusual circling motion visible on this flight tracking software.

::What are experts looking for?

A U.S. aviation safety expert told Reuters that investigators would look at aspects like weather and examine to what extent the engines and controls were functioning properly, to help identify what caused the loss of control.

They do have the black box from the plane to assist them which consists of the Cockpit Voice Recorder and the FDR Flight Data Recorder.

::What are some potential causes?

Videos of the crash analyzed by aviation experts led some to speculate that ice had built up on the plane. On Friday, the airline said ice was predicted at the altitudes in which the plane was flying, but that it should have been within an acceptable level.

A Brazilian aviation engineer and crash investigator said he is almost certain ice caused the accident, judging from videos he has seen.

An American professor in a university department of aeronautics and astronautics said it may have been an engine failure on one side, mismanaged by the crew, which could heave led to the rotation downward.