Moments before the crash of a corporate airplane that killed all eight people on board, the control tower had warned the crew that the plane was too low, a federal safety official said.

The Circuit City (search) plane was at 300 feet at the time but should have been at least 900 feet above the ground as it approached the Pueblo (search) airport, said chief crash investigator Frank Hilldrup of the National Transportation Safety Board (search).

"There was something called a minimum safe altitude warning. We believe (pilots) got a warning ... basically 'check your altitude,"' Hilldrup said Friday.

The twin-jet Cessna Citation C-560 was stopping to refuel when it crashed Wednesday during a flight from Virginia to California. Both pilots, four employees of the electronics retailer and two representatives of other companies were killed, the company said.

An aviation expert, Michael Hynes of Hynes Aviation Services, said the warning probably did not come in time for the pilots to avoid the crash.

"I don't think the tower alert would have made a difference," he said, estimating that the pilots only had seven seconds to react, based on typical landing speeds.

Hilldrup has indicated the pilots did not make a distress call.

Attention in the investigation has focused on wing icing because there was freezing drizzle and fog in the area, and the crews of three other planes had reported icing conditions. Ice accumulating on wings can disturb the smooth air flow needed to keep an airplane aloft.