Madrid - One week after a Spanair MD-82 passenger plane crashed at Madrid airport, killing 154 people, the causes of the accident remain unknown, Spanish media reported Wednesday.

The pilot did not report anything to the control tower after take- off, the daily ABC said.

The plane hit the ground tail first outside the runway, according to a commission investigating the accident.

The tail then broke off and the plane bounced for 1,200 metres, hitting the ground three times and suffering increasing damage.

Witnesses have said the plane did not have the engine power to take off. The reverse system, which helps aircraft to slow down when landing, was turned on on one of the two engines. The reason for this is unknown.

The engines are still in relatively good condition, making it possible to examine them, said Francisco Javier Soto, head of the commission. The black boxes were sent to Britain for analysis.

The commission expected to issue a preliminary report within a month.

Sixteen people remain at hospital after two were released. A funeral mass will be held for the victims on September 11. (dpa)