[Shermy]

Smoke could have been because the pilot was misusing the plane, his aim to crash into the building, not airplane maintenance. He called an SOS because he thought he might have to abort, had second thoughts and knew he could get to the target.

[Travis McGee]

Smoke seen coming from plane before impact reports: early 4th hand "eye witness" reports relayed via cell phone and in translation about such details have a VERY low reliability factor.