I've said it before, and the next media report of "smoke" in the cockpit, I'll probably say it again. If the engine is the problem, then pilots and passengers might have been exposed to oil FUMES, or MIST, which occurs frequently when an engine leaks oil in the compressor stage forward of the bleed air inlets.
That compressed air can be 600 degrees or much hotter. Common jet engine oils contain trycresyl phosphate, which is a neurotoxin. MOST IMPORTANTLY, this is a flight safety issue. The flight crew can be intoxicated by the fumes, and their cognitive function, and motor coordination seriously degraded. That could have influenced the pilots' non-standard communications in this instance. I thought what he said was exceedingly clear, emergency, smoke, roll trucks. The controller didn't mis-hear his words, he just didn't think it was real. I don't care if he said something as non-standard as "5912 is on fire, we're landing, roll trucks," the controller can interpret and declare the emergency, and should default to "this is real" not "this is BS."
The crew and passengers should be tested for TCP exposure, and the airline should be required to inform everyone of what substances they were breathing, so they can get appropriate medical attention. Doctors will misdiagnose unless they know about exposure to organophosphates. Blood tests should be done within the first 48 hours if possible. Pilots are largely unaware of toxic bleed air contamination, and can take a cavalier attitude, which is unfortunate.
The protocol for blood testing is here:
http://www.baileygreer.com/library/L..._ALL_FORMS.pdf
The medical protocol for physicians to use after a fume event is here:
http://www.baileygreer.com/library/F..._Bleed_Air.pdf