Three Brazilian navy vessels were dispatched early Wednesday to the wreckage site of the Air France flight 447 after it crashed into the Atlantic on Sunday night after taking off from Rio de Janeiro destined to Paris.

Search operations will be focused on trying to recover the black box which according to Brazilian defense minister, Nelson Jobim, there may be “great difficulty in finding it”. Jobim said the depth will vary “between 2,000 and 3,000 meters” as the “black box does not float”.

According to reports published in Brazilian newspaper Folha, at the point where the flight was last seen through radar, the pilots were not flying at the altitude specified in its flight plan. The reason for this remains unknown.

The plane, carrying 228 people, lost contact with ground controllers after leaving Rio de Janeiro for Paris on Sunday night. The crew made no distress call before the crash, but the plane's system sent an automatic message just before it disappeared, reporting lost cabin pressure and electrical failure.

Air France will release the official passenger list today which will however be incomplete after families of victims asked for names not to be disclosed.