Commercial Fixed Wing
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Deviation / Discrepancy - Procedural Hazardous Material Violation; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Company Policy; Human Factors; Procedure
We received an ACARS message that told us a box of horse tranquilizers may have been left on the aircraft from the previous flight.  We did a search of the cockpit and found it in the storage area next to the Captain's seat.  This bin usually contains the EFB charger and cable; extra headset; Ipad mount; and maybe a water bottle or two.  It was a small black box; it blended in very well with the other jumble of black things.  I missed it on the my cockpit inspection. Horse charters are unusual.  Flight crews don't do them often and the requirement for the PIC to maintain control of the dangerous drugs the handlers carry is easily forgotten on block in. Treat that box of tranquilizers in the same way we deal with gear pins and pitot covers.  Place a light weight; bright orange; pouch with a long orange flag in the logbook. The pouch and flag should say 'DANGEROUS MATERIALS' in big letters on the outside.  Require a logbook write-up when the pouch is used.  The write-up is cleared when the pouch is re-stowed.  If the flight crews; AMTs; and cleaning crews see that pouch and flag; they will notify OPS.
Captain reported a Dangerous Goods container was erroneously left on board from a previous flight.