Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Vehicle
General None Reported / Taken
Human Factors; Aircraft
After parking at gate; flight crew were informed of damage to left horizontal stabilizer.  It appeared to have been struck by a tall ground vehicle.   I considered the aircraft inoperable after reviewing the damage.  The FO noted no damage during his external inspection; and felt that he would have easily noted the damage had it appeared during that time.  We concluded the damage was likely caused by a catering truck at ZZZ; after the walk around was already complete.  The crew was not informed of the damage and continued the flight to ZZZ1.  We had no idea.A failure on the part of service crew in ZZZ to notify the flight of damage when it occurred.  This resulted in the flight continuing when not air worthy.  The flight and landing went without incident; until ZZZ1 reported the damage to the flight crew after arriving at the gate.It is impractical for the flight crew to perform an external inspection after all external service equipment is removed and the cabin door is closed.  The last opportunity to look over the aircraft is the push back crew.  Perhaps wing walkers could walk all the way back to the tail on their respective sides and examine the airplane for anything unusual.  This information could then be forwarded to the tug driver; who would in turn forward to the flight crew.  Something like 'external equipment clear; inspection complete; no damage noted.'
Air carrier Captain reported they flew an unairworthy aircraft after it had been struck by a catering vehicle on the horizontal stabilizer pre-flight.