The reported cannabis finding involving an Air India pilot has arrived at precisely the wrong moment for a serious aviation investigation. An aircraft suffered a sudden loss of altitude, passengers and crew were injured, and public anxiety is naturally high. In such circumstances, a drug test can quickly become the most convenient explanation. It should not become the explanation before the evidence warrants it.

The distinction matters because aviation safety depends not merely on identifying something potentially wrong, but on establishing whether it was actually relevant to an incident. Cannabis can impair attention, motor control and the ability to manage complex tasks. That makes its possible presence in a pilot’s system a legitimate matter for investigators. But detection is not the same as impairment, and impairment is not the same as causation. This is where the limitations of cannabis testing become important. Unlike alcohol, for which blood concentration has a reasonably established relationship with impairment, the presence of THC does not provide investigators with a dependable clock.

Depending on the test and the individual, traces may remain after the effects have disappeared. A positive result can therefore........

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