Air Florida's maintenance chief at National Airport yesterday told federal investigators that he saw snow on Flight 90's left wing after it was de-iced at the departure gate. He said he thought it was dry snow that would blow off and did nothing about it.

Juan Cruz, testifying at National Transportation Safety Board hearings into why Flight 90 crashed Jan. 13, said he had never received training in de-icing and assumed that the American Airlines crew who de-iced the plane on contract knew how to do the job correctly.

Testimony Thursday indicated that as Cruz looked on, the crew de-iced the Boeing 737 unevenly and violated Air Florida's maintenance manual by failing to cover the engine inlets to protect them from the de-icing spray.

One of federal investigators' prime theories about the crash is that Flight 90 took off laden with ice or snow that damaged its wings' ability to generate lift. After 30 seconds in the air, the plane struck the 14th Street bridge and plunged into the Potomac River, killing 78 people.

Testimony at the hearings has brought to light widespread ignorance of de-icing regulations within the aviation industry and broad disagreement over how to de-ice and how much protection antifreeze fluids give against buildup of new snow.

Cruz's testimony and written statements indicate he did not make a detailed inspection of the jet after the de-icing was completed. Investigators are trying to determine whether anyone gave the plane a thorough going-over just before it left the gate.

Cruz told investigators he thought the captain is responsible for making sure the plane is free of ice or snow. But after listening to an excerpt from Air Florida's manual which appear to assign responsibility to "Air Florida Maintenance Personnel," he said that they referred to him.

Though Air Florida requires that engine inlets be covered during de-icing, Cruz said he had never seen that done. "I have never discussed with American the procedures for de-icing the airplane." American Airlines does not operate any 737s.

Cruz said he had never seen two bulletins from Boeing warning airlines that 737s can pitch up abruptly when taking off in icy conditions, posing control problems and increasing the chances of stalling. Boeing has found that ice on a 737's leading edges can help cause the pitch-up and has cautioned against using reverse thrust before take-off, because snow the engines melt can refreeze on the plane as solid ice.

Yesterday Cruz testified that through a tractor driver he had suggested to the pilots that they use reverse thrust to help pull the plane away from the gate. They did so, kicking up swirls of snow that board investigators believe may have refrozen on the plane.

In other testimony yesterday the president of Trump Inc., the manufacturer of the de-icing equipment used on Flight 90, said he was "shocked" to learn that tests showed American Airline's antifreeze concentrate to be 80-to-83 percent pure. His company assumes 93-to-95 percent purity in determining water-antifreeze mixes, Ted Trump said.