Date: 201812
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ground ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: All operations were normal and CA (Captain) and FO were in the green. A/C (aircraft) was planned to be heavyweight and CA/FO operational discussions while at the gate passenger boarding included emphasis on maximum taxi weight awareness and [takeoff performance] numbers with further highlights of environmental conditions (weather); taxi routing; and runway use. These items were further reviewed during the 'departure briefing'. Aircraft pushback began with pushback clearance from ground initially stating (from memory) 'cleared to push; push into the alley; hold short of taxiway [X]' and was quickly updated to 'cleared to push onto taxiway [X]; tail west.' Once the A/C was in the pushback 'drop off' position (on [X]; tail west); FO was completing engine start. FO heard the CA tell the Tug Driver 'Thank you for the pushback; have a great day' and the Tug Driver acknowledged. FO heard the CA call 'I have a salute' and the ground crew (Marshaller and Wing Walker) were observed to no longer be in front of the aircraft and had cleared the area (not in sight/returned to terminal area). FO completed 'After Start Flow' and set flaps to '1' per the [takeoff performance] for XXR. 'Flaps 1 Taxi' call was made and FO called ground for taxi and ground replies 'Taxi to XXR; [via taxi route.]' Both CA and FO are 'heads up' and clearing ahead and the anticipated turn. CA carefully applied (we are aware that we are pretty heavy) taxi thrust (aircraft and almost immediately a noise was heard from the vicinity of the nose wheel. CA immediately chopped thrust to idle. CA and FO think/say 'That was odd.' Additional clearing of the area was accomplished. CA and FO discuss likely possibilities and conclude nose wheel area noise was result of a taxiway anomaly/depression. CA carefully applied taxi thrust (heavyweight awareness) and CA and FO both observe the Tug Driver/Tug pulling away backwards at what appears to be an unusually high speed and directly to a tug-parking area at the terminal (by gate.) Simultaneously upon first flash of the orange Tug (entered field of view); CA chopped thrust to idle. A/C brakes are set; A/C position is NOT moved; ATC-Ground is notified that we will hold our position on taxiway [X] for a maintenance inspection and post that inspection; will taxi back to gate. Appropriate procedures; coordination; and paperwork were accomplished with Operations; Dispatch; ATC; Ramp; and Maintenance to resume the planned flight with delayed generated by this incident. Both the CA and the FO; having completed the thorough follow-up actions; coordination; and paperwork; felt solidly in the green and were confident with their decision to continue with [the flight.]From the information I have available; it appears that the Marshaller and Wing Walker (ground crew) gave the all clear signal and completely vacated their position in front of the A/C prematurely. The Marshaller/Wing walker vacated their position in front of the A/C prior to the Tug/Tug Driver vacating his position from below the nose of the A/C. The tug appeared to be the 'new' style of tug with low profile and the 'lobster/clamp' style of appendage to 'grab' the nose wheel (i.e. not the 'tow-bar' style). Of note; it was/is completely impossible to see any portion of this tug from either the CA or FO positions; which is common for several tug types and serves to further emphasize the criticality of the Marshaller/Wing Walker NOT giving the all clear signal and NOT vacating their position in front of the aircraft. In summary; it appears that non-standard/improper procedures were executed by the Marshaller/Wing Walker/Tug Driver and CA/FO had no way of knowing the Tug/Tug Driver were still below the nose of the A/C.We can all - always - learn from every unusual/abnormal incident any one of us may experience during operations. It appears there was likely a breakdown in procedures of the ground crew (Marshaller/Wing Walker/Tug Driver). For this incident; I humbly submit that I; as the FO (even though flows/procedures/timing/engine starts may have me in a 'heads down' mode) can better back up the 'CA+FO Team Effort' (i.e. operations safety) by being more consistently deliberate in monitoring the 3 parties of the standard pushback (Marshaller; Wing Walker; Tug Driver) to ensure that all three have vacating the vicinity of the A/C.


Second narrative: After pushback and engine startup we received a salute from the ground crew that pushback was complete and we were cleared to taxi. I acknowledged with a taxi light and a salute and the ground crew left. As I brought the power up to taxi we felt a 'clunk' and immediately stopped the plane. The First Officer and I looked at all systems indications and did not find anything unusual. We felt that perhaps we were just in a low spot of the taxiway or an expansion joint and attempted taxi again. As I brought the power up to taxi we saw the push tug come out from underneath the aircraft. We immediate stopped. Realizing that we must have come in contact with the tug on the initial application of power we contacted operations and maintenance. We had maintenance inspect the nose gear for damage then returned to gate. I made a maintenance entry and after inspection and sign off by maintenance we continued the flight.I had a pin and a salute to commence taxi. I have no idea why we were given the okay to depart while the tug was still below the aircraft. I have no way to see if the tug is still there. I know that I did not see the tug depart and should have been more aware of its location; but my focus was on the crew telling me we were cleared to taxi. The area of visibility available to me does not include a tug underneath the nose of the aircraft.As far as I know we complied with all procedures correctly. I can't speak for the breakdown in communications between the ground crew and why they cleared us to taxi. For my part my focus as to the clearance to taxi has always been to receive a pin and a salute. Now I will be more conscious as to the location of the tug when I receive the salute.


Synopsis: A321 flight crew reported starting to taxi after pushback and salute with the tug near the nose gear.