Urine, blood and even saliva can show that someone was exposed to THC, but they cannot reliably establish when it was used or whether the person was impaired at a particular point several hours earlier, according to Marcotte. Saliva is more closely linked to recent use, but can still detect THC many hours - and potentially a day or two - after consumption, he says.

Experts believe the question is not simply: Was the pilot using marijuana?

It is threefold: Was cannabis consumed? Was the pilot impaired while flying? And did that impairment contribute to the aircraft's sudden loss of altitude?

The first may soon be answered. The other two are considerably harder. .

Basically it's about measuring impairment and not just presence of cannibanoids