DENVER — Dozens of flight attendants for Frontier Airlines held a picket at Denver International Airport on Thursday afternoon to protest contract negotiations that have stalled.

The flight attendants’ vice president of the union Andrienne Prince said she remembers what flight attendants gave up in 2008 when the airline filed for bankruptcy.

“We took cuts in vacation, sick time, hourly wages. … The company doesn’t feel like they should invest in their employees,” she said.

This should be the best of time for Frontier since the airline has plans to add nine additional planes by the end of 2017, plus hire 800 more flight attendants and 300 pilots.

“They’re doing phenomenal. They’re as profitable as they’ve ever been,” Capt. Brian Ketchum said.

Yet Ketchum, who represents the pilots’ union, said the airline isn’t sharing profits with employees.

“Everything seems to be focused around cost-cutting and outsourcing,” he said.

“In October, the pilots’ union demanded a federal mediator because of stalled negotiations.

It’s not just the employee unions who are frustrated.

“In the future, I would probably try another airline before I go back to Frontier,” passenger Lynn Carroll said.

Carroll sat on the tarmac for 94 minutes after her plane landed at DIA.

“We kept saying well why aren’t they just putting us into another gate, and that’s when we found out there aren’t enough ramp people to accommodate us,” Carroll said.

It was the same experience for passenger Ernest Sandoval.

“They need to know that their customers shouldn’t be treated like freight,” he said.

He too sat on the tarmac for 90 minutes with his 12-year-old daughter, who has autism.

“Once her anxiety starts going, our anxiety starts going and it`s just multiplying,” Sandoval said.

Passenger Bill Holzman said he couldn’t believe how his delay at Los Angeles International Airport kept multiplying, after a Frontier gate agent told him his morning flight would only be delayed an hour.

“We didn’t actually get on the plane until 9:12 p.m. that evening, so 12 hours at the airport with no communication,” Holzman said.

The Department of Transportation tracks performance issues for the 12 major airlines.  The most recent stats cover July and August, and found Frontier ranked last for on-time performance and 11th for mishandled baggage.

The figures show the airline was seventh for oversales, which is when an airline bumps a passenger because the plane is overbooked. And the airline ranked near the bottom for overall consumer complaints, 11th.

Frontier CEO Barry Biffle said the airline now ranks third best when it comes to fewest cancellations.  He said that shows it’s committed to customer service.

“Our on-time performance is better this year than it’s been in years, yet we have lower costs,” Biffle said.

Frontier blamed the tarmac troubles on its ramp operations vendor Swissport and fired the company in September. The airline hired a new contractor, Simplicity USA, to take over ground services.

“I`m disappointed in the failures we had,” said Biffle, who was photographed slinging bags on the tarmac because ramp operations were understaffed.

Some employees criticized Biffle for working the front lines when a vendor failed to perform this summer.

“If we weren’t out there, I would hear the opposite. Where were you?” Biffle said.

Employees on the picket line said low fuel costs and low wages are the reason why there are lower costs.

One thing the sides agree on is that the airline is finally making money for the private equity firm Indigo that owns it.

“It is true, that this airline failed for 20 years, went thru bankruptcy and never made money. We joked a year ago, that we made more money in the first year that we took over the company than they made in 20 years. Well, that’s easy to do when you never made money,” Biffle said.

Biffle joined Frontier in 2014 and said the airline has implemented new changes to better communicate with passengers, including a new website, mobile app and text alerts. The DOT’s performance numbers for November airline rankings will be available in two months.