And last week, the airline created its biggest scandal since last April when a passenger's 10-month-old puppy died after the passenger was forced to place it in the overhead bin during a United flight from Houston to New York.
RELATED: All of United Airlines' recent PR nightmares
All of United Airlines' recent PR nightmares
All of United Airlines' recent PR nightmares
1. United Airlines Flight 3411
Footage of Dr. David Dao being dragged off United Airlines Flight 3411 from Chicago, Illinois, to Louisville, Kentucky, went viral on April 10.
The incident, in which Dao lost teeth and broke his nose, sparked international uproar and turned into a public relations nightmare for the carrier.
Dao will be suing the company, according to his attorney.
2. Second United Airlines passenger comes forward
Amid the social media firestorm set off by Dr. Dao's incident, a second passenger came forward to say that he, too, recently experienced mistreatment on a different United Airlines flight.
Geoff Fearns, 59, told KCAL he was removed from his first-class seat on a flight from Kauai, Hawaii to Los Angeles, California last month.
Although Fearns said he tried to resist the flight attendant's orders at first, he eventually caved once she threatened to have him put in handcuffs.
3. Scorpion falls from overhead bin and bites passenger
A Canadian couple's Mexican vacation came to an unfortunate end when they were flying home to Calgary from Houston on April 11.
Richard and Linda Bell were on a United Airlines flight when a scorpion fell from an overhead bin onto Richard's head.
He dropped it on his plate, then picked it up again, when the scorpion stung him.
The animal was stomped on and thrown in the toilet.
Emergency services were called in, but Bell was reportedly not in distress. He declined medical treatment.
4. Woman claims she was sexually harassed by drunk man on United Airlines flight
A New Jersey woman said that United Airlines flight attendants continued to serve alcohol to a visibly inebriated passenger after she complained that he sexually harassed her.
Jennifer Rafieyan was traveling from Newark, New Jersey, to Phoenix, Arizona, with her 12-year-old daughter when the drunken passenger was escorted onto the plane.
Over the course of the flight, Rafieyan said the man repeatedly groped her and rubbed her legs and knees, while occasionally kissing her hands and putting his head on her shoulder.
Rafieyan reported the passenger to a crew member after her daughter got up to use the bathroom, but it did little to help her situation.
"She said, 'I'm so sorry. We felt really bad putting him next to you, but there was nothing we could do. He was doing the same kind of stuff to the other flight attendant,'" Rafieyan recalled.
5. Couple kicked off United flight on way to their wedding
Michael Hohl and Amber Maxwell had boarded their flight when they noticed a passenger napping across the row they were supposed to be sitting in.
Instead of waking up the snoozing man, the pair decided to sit a few rows in front of their assigned seats.
Hohl said that after he and Maxwell sat down, a flight attendant asked if they were in their assigned seats. When the couple said no and explained why they had moved, Hohl said the attendant declined their request for an upgrade and asked them to return to their original seats.
Hohl said that although he and Maxwell did as they were told, a U.S. Marshall later boarded the flight and asked them to get off the plane.
6. United Airlines CEO's heart transplant comes under scrutiny
Following United Airlines CEO Oscar Munoz's apology over Flight 3411, people began questioning whether his wealth played a role in the heart transplant he received last year.
Munoz had a heart attack on October 15, 2015, one month after he took over as United's new CEO.
Less than three months later, he received a new organ.
Since the waiting list for a new heart was reportedly up to 4,200 people at the time, questions have risen about how he was able to get a new heart without waiting very long.
7. Dad accused of trafficking his own daughter on United plane
The wife of a Mexican man who was accused of trafficking his own 3-year-old daughter on a United Airlines flight spoke out about the incident on April 17.
Maura Furfey, a Spanish teacher and mother of three, says that her husband and daughter were returning from a trip to Mexico to visit her husband's mother and great-grandmother, "who they see but once a year."
Apparently another passenger, who Furfey says was "obviously inebriated," expressed concern to an airline employee that the fair-skinned child didn't look like her Mexican father, raising suspicion that he had kidnapped her.
The mother of three says she burst into tears when she learned the details of what her family had gone through.
8. United Airlines stock plummets $800 million amid controversy
United Continental lost about $800 million in total value the day after the video of Dr. Dao being dragged off Flight 3411 became a major news story.
Shares in the company declined about 3.8 percent in mid-morning trading, a steep drop for a major company like United.
9. Woman claims United Airlines employee forced her to back of plane in tears without explanation
A New York woman filed a $150,000 lawsuit against United Airlines, claiming she was forced from her business class seat to the back of the plane by an employee without any explanation during a flight last year.
Karen Shiboleth, a 24-year-old Columbia graduate, was traveling to London to attend a master's degree program at Kings College on September 10, 2016.
Shiboleth claims that ten minutes prior to take off, a United employee boarded the craft and demanded she vacate her seat in United BusinessFirst and move to the back of the plane.
The lawsuit alleges that nobody would explain to Shiboleth why she was being moved, and that when she expressed her confusion, the employee took her arm "without consent" and forced her to a middle seat in the back of the plane.
To make matters worse, the unidentified worker reportedly called her a "c--t" during the interaction, bringing Shiboleth to tears.
10. Professional golfer claims his clubs were snapped on United Airlines flight
An Australian professional golfer took to Twitter on April 24, claiming his golf clubs were destroyed during a recent United Airlines flight.
Veteran golf pro Matthew Goggin said he opened his checked bag after his trip, only to discover that his precious clubs were snapped in two.
"First time in 20+ years I've opened my bag to find this..." he wrote. "I was going to complain but I must admit I'm a little intimidated by United."
11. Giant rabbit mysteriously dies aboard United Airlines flight
Simon, a 35-inch behemoth, was traveling from London's Heathrow to Chicago's O'Hare to meet his new "celebrity owner" when he mysteriously died in the airline's care.
Annette Edwards, Simon's breeder, says that both she and Simon's buyer are extremely upset and confused by the incident.
"Simon had a vet's check-up three hours before the flight and was fit as a fiddle," Edwards said. "Something very strange has happened and I want to know what. I've sent rabbits all around the world and nothing like this has happened before."
Simon was the son of the world's current largest rabbit, Darius, who is a whopping 51 inches long.
The 10-month-old rabbit was reportedly on track to out grow his father and eventually steal his title.
Airline expert George Hobica says the airline's failures start at the top, with CEO Oscar Munoz.
"It's just a lack of integrity in their leadership," Hobica told Business Insider.
Munoz, who previously ran the freight rail company CSX, became the airline's CEO in September 2015, after his predecessor, Jeff Smisek, resigned in the midst of a bribery scandal. The airline was a mess when Munoz began his tenure, as years of cost-cutting measures and tense negotiations with labor unions had damaged employee morale.
Beginning with his first year, the company's operational metrics improved as it decreased delays and lost a smaller amount of baggage while increasing its number of flights. In its fourth-quarter earnings report in January, the company said it "achieved a record-setting year for operational reliability, including best on-time departure performance, fewest cancellations, and best baggage handling performance" in 2017.
RELATED: Best airlines in the US
9 best airlines in America
9 best airlines in America
9. Hawaiian Airlines
Previous rank: 8
Why it's here: Hawaiian finished last on the TPG list. The Honolulu-based airline's premium ticket prices and Hawaii-centric route network fell victim to TPG new metrics which increased focus on airfare and network size.
Previous rank: 4
Why it's here: JetBlue suffered the most significant drop in this year's rankings. The New York-based airline struggled with on-time arrivals, baggage and change fees as well as customer satisfaction. JetBlue's position as a boutique carrier hurts it rankings with respect to the size of its route network as well as the lavishness of its frequent flyer program.
7. Spirit Airlines
Previous rank: 10
Why it's here: Spirit jumped three spots in the rankings due to its improvement in areas such as the number of lost baggage while also benefiting from the missteps of its rivals and the merger of Alaska and Virgin America.
Previous rank: 5
Why it's here: American Airlines didn't make many moves apart from a one spot from after the Virgin/Alaska merger. The airline struggled with on-time arrivals, fees, lost baggage, and customer satisfaction.
5. Frontier Airlines
Previous rank: 9
Why it's here: Frontier Airlines made a surprising jump up the rankings. The ultra-low-cost carrier benefitted from its route expansion and its improvement in baggage handling.
4. United Airlines
Previous rank: 2
Why it's here: United Airlines rocky 2017 caused it to fall two spots, but not for the reasons you'd expect. United saw marked improvement in operational effectiveness with the number customer complaints down 17% while also decreasing the number of people involuntarily bumped from flights. However, the airline couldn't keep up with its rivals in areas such as airfare and the quality of its airport lounges.
3. Delta Air Lines
Previous rank: 7
Why it's here: Delta made big strides in airfare, the involuntary bumps, and its frequent flyer program while maintaining its high rankings in on-time performance, lost baggage, and the size of its route network.
2. Southwest Airlines
Previous rank: 6
Why it's here: Southwest improved four spots over the past year thanks to lower airfare and the expansion of its sizable route network. The airline's stellar customer satisfaction score and its free checked baggage policy also helped.
1. Alaska Airlines
Previous rank: 1
Why it's here: Alaska Airlines maintained its top spot by scoring in the top three in several key criteria including airfare, on-time arrivals, customer satisfaction, baggage handling, and its frequent flyer program.
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Executives and low-level employees have a strained relationship
But the company's operational and financial performance has still lagged behind some of its rivals, and efficiency doesn't always result in great customer service. While Munoz has taken steps to improve United's culture, it may not be enough, according to Charles Leocha, president of the airline passenger advocacy group Travelers United.
Leocha has talked to United employees over the years, and he's heard that the historically strained relationship between the airline's management and low-level employees remains, despite recent improvements.
"I've heard that it's far better than it used to be, but there's still a lot of animosity," he told Business Insider.
The company's response to its employees showed that it may be more sensitive to their concerns under Munoz, but the fact that it changed its bonus system in the first place, while trying to persuade its employees the changes were good for them, reveals that there's more work to be done.
Munoz has taken some positive steps, but he still has work to do
In March, the airline introduced "core4," a new training program for employees who interact with customers. The program was designed to improve their efficiency and prevent customer service issues from escalating into scandals. But a recent report from Inc. indicates that additional training may only solve part of the problem.
"Morale isn't good," a United employee told Inc. "There's so much bad blood after the lottery bonus scandal. Everyone is wondering how they could even suggest something like that. And we still don't know whether they're going to take our bonuses away anyway."
When a company's employees feel mistreated, they're more likely to mistreat their customers, according to Hobica.
"An underpaid and overworked staff will be unhappy, and they'll take it out on customers," he said.
Munoz, then, is in a difficult position. His 93% employee-approval rating on Glassdoor is higher than those of the CEOs for American, Delta, and Southwest Airlines. The Inc. report noted that many employees blame United president Scott Kirby for their troubles, rather than Munoz.
But Munoz is the CEO, and whether he deserves a majority of the blame or not, he'll be held to account for the airline's combination of financial underperformance and public-relations missteps.
Under Munoz, United began a process of introspection that has yielded positive results. But, so far, it hasn't been enough. United's challenge is to continue looking inward and eventually find answers, Hamlin Transportation Consulting President George Hamlin told Business Insider.
"It needs to be fixed, or it will get worse," he said.