2 United Airlines planes touch tails at SFO, causing damage to wing

SAN FRANCISCO INTERNATIONAL AIRPORT (KGO) -- A minor collision was reported between United Airlines planes at San Francisco International Airport Monday night, putting Labor Day travel on hold.

A jolt that felt like an earthquake -- that's how some United Airlines passengers described the moment when the two planes collided, causing significant damage.

One plane damaged another while it was pushing back from the gate, causing the two tails to collide. Passengers on the Boston-bound flight shared on social media that it felt like an earthquake.

"I think that's probably a good description," NTSB News Talk Host Max Trescott said. "You know, we're used to sitting in an airplane at the gate and things are very calm and quiet, and this definitely would feel very unusual. I think earthquake is probably a good description."

Thankfully, United Airlines said in a statement there were no injuries and passengers on both planes deplaned normally before they continued with their travel.

MORE: Delta plane wing clips empty aircraft during pushback from gate in Atlanta

ABC7 News spoke with Aviation Expert Max Trescott about the collision. "What happened is a somewhat uncommon event, but it's not totally unheard of," Trescott said. "What's unusual is that the aircraft hit another aircraft. Usually what happens when this occurs, and that probably happens once a year around the world, it rolls into the tug and so there's a lot less damage."

The FAA is investigating what went wrong, but Trescott has some theories.

After loading up with passengers, planes are pushed back from the gate by what's known as a tug, driven by the airline's ground controller. At this time, pilots don't have control of the plane because there is no reverse.

Trescott says NTSB reports found a number of incidents due to a failure or improper maintenance of the tug, including in Australia this past July.

"This may have been a case of either an operator turning the wheel at too sharp an angle, moving at too high a speed," Trescott said. "Most likely it was some operation type of error, but it could have been also a failure to properly maintain the tug."

It was a common airport procedure, pushing back from the gate. But in this case, there was an uncommon result.

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