Date: 202105
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Second aircraft: Commercial Fixed Wing
Aircraft component: Winglet
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Aircraft
Detector: Person Flight Crew
When detected: Taxi
Result: Aircraft Aircraft Damaged; Flight Crew Returned To Gate
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Aircraft was directed to taxi from gate 1 to Runway XXL via Taxiways 1; 2; 3; 4. While on Taxiway 3; turning right to join Taxiway 4; both crew members noted an aircraft that appeared to have just been pushed back from gate 2. It was also agreed by both crew members that the tail of the aircraft appeared to be just inside the ramp boundary line. Approaching the aircraft at gate 2; the FO noted that the right wingtip was on the boundary line. The Captain then stated that he was going to deviate left of the taxiway centerline for additional clearance and the FO acknowledged. Approaching the aircraft; the FO was monitoring the right wingtip. From the cockpit angle the wingtip appeared to have approximately five feet of clearance and this was communicated to the Captain. The FO continued to monitor the wingtip until it appeared to initially pass the tail of the other aircraft outside of gate 2 and then announced it was clear to the Captain. It was at this time the right winglet struck the horizontal stabilizer. (Aircraft  speed was approximately 5 knots.)  The FO then called out to stop multiple times. The Captain stopped the aircraft and made an announcement for the Flight Attendants and Passengers to remain in their seats. The Captain verified with the Flight Attendants that everyone was OK. The crew then coordinated with Ground Control and Operations to return to gate 3. An ACARS message was also sent to Dispatch while waiting for a gate assignment. It is the FO's initial assessment that the wingtip must have started to pass on the opposite side of the horizontal stabilizer of the aircraft outside of gate 2; but incorrectly determined that it was on the near side based off the cockpit angle and understanding that the Captain had deviated left of the taxiway for more clearance. There were no distractions and the crew communicated clearly.  Actions that could have prevented this incident would have been if the crew had stopped on Taxiway 4 and waited for the aircraft at gate 2 to move and provide more clearance. Additionally; the FO could have better assessed the wingtip spacing.


Second narrative: We were cleared to taxi from [gate] 1 to [Runway] XXL via [taxiways] 2; 3 and 4. As we were joining 4; I noticed an aircraft facing terminal at [gate] 2; which appeared to be just inside of the movement area line. I mistakenly assumed it was an aircraft that had just pushed and that he was waiting to taxi. My expectation bias was that he would not have been pushed deep enough to interfere with Taxiway 4. As we were NE bound on [Taxiway] 4; I steered aircraft left of taxi; centerline to give more clearance around other aircraft. I asked FO how we looked on wingtip clearance. The FO stated; 'We are clear by 5 to 10 feet.' As we were passing behind the aircraft I felt that a main tire hit a pothole. As I asked what that was; I felt another 'bump'. The FO stated 'Stop. Stop.' I brought the aircraft to a stop and the FO told me we struck the other aircraft. I would estimate we were at a speed of 7 to 8 knots when the contact occurred. We began our taxi on #2 engine. I believe the second engine start was complete prior to contact. There was a typical level of chatter on ZZZ Ground frequency; which was busy. After the contact; I stopped the aircraft on Taxiway 4 and set the parking brake. We reported the incident to Ground Control. While I made a PA to the cabin to remain seated; the FO notified operations to coordinate a gate return and contact Maintenance. We returned to Gate 3 without further incident.Task Loading - I did a poor job of managing task loading. ZZZ is very busy and congested on the ground. With multiple aircraft moving in a densely packed area; I should not have opted for Single Engine Taxi (SET).  This would have reduced the workload on both crew members and perhaps allowed for better situational awareness as we were moving towards the departure runway. Risk Management- I did not properly balance the risk of aircraft contact with continuing on the taxiway. Had I stopped and waited on the other aircraft to move well clear of taxiway; I would not have assumed that unnecessary risk. This also relates to rushing and trying not to clog up a taxiway. I should have set the brakes and not moved forward until aircraft in question was well clear.


Synopsis: Air carrier flight crews reported that during taxi from the gate the aircraft's right winglet struck the horizontal stabilizer of another aircraft at an adjacent gate. The flight crew of the other aircraft reported they were waiting for the marshallers to get into position at the gate and felt the aircraft move when it was struck.