The airline industry is betting against Spirit Airlines.

“If Spirit suddenly goes out of business it will be incredibly disruptive, so we’re adding these flights to give their customers other options if they want or need them,” said Patrick Quayle, United’s head of network planning and alliances.

Frontier, which is gunning for Spirit’s position as the largest U.S. ultradiscounter, has seized on Spirit’s pullback, announcing plans to add service along several routes Spirit serves.

“We want to be America’s low-fare airline,” said Frontier Chief Executive Barry Biffle. “And we see an opportunity.”

Spirit, which filed for chapter 11 bankruptcy last week, has assured customers they can continue to book future flights and use their tickets. Chairman Robert Milton said in a recent interview the airline has no intention of liquidating: “It needs its costs restructured and to get its mojo back.”

Spirit for years played the role of an airline industry maverick, charging ultralow fares with fees for almost everything.

A Spirit spokesman on Thursday described United’s plans as “wishful thinking” from an airline that wants to drive a low-cost competitor out of business in order to charge more.

“While we appreciate the obsession certain airline executives have with us, we’re focused on competing and running a great operation,” he said.

But even a weakened Spirit is good news for competitors, which stand to benefit from reduced supply of seats.

In years past, Spirit has played the role of an industry maverick. It was willing to fly its bright yellow planes into big cities and go head-to-head with the legacy airlines. Its nickel-and-dime approach to sales—charging bargain basement fares with fees for almost everything—sometimes annoyed customers. But it also forced competitors to lower fares, and in many cases, adopt similar practices.

Now Spirit plans to shrink its fleet and retrench to key cities such as Orlando, Fort Lauderdale and Detroit. It announced this week that it is pulling out of 11 cities and scrapping plans to add service to one more—about 4.5% of its planned flights.

A three-year saga of failed mergers, changing postpandemic travel patterns, and new competitive weapons deployed by big airlines brought Spirit to this point. Spirit’s losses since the beginning of 2020 have more than wiped out all the profits it made since 2006, when it shifted to embrace the ultradiscount model.

Struggling to find its footing after a federal judge last year struck down a $3.8 billion acquisition by JetBlue Airways, Spirit filed for its first bankruptcy in November. But it didn’t seek to use the power of chapter 11 to renegotiate contracts with aircraft lessors or other obligations, as other airlines have historically done after filing for bankruptcy.

The company opted instead for a quick balance-sheet fix that minimized its time spent under court protection, hoping to avoid a lengthy and expensive process. The earlier bankruptcy only affected Spirit bondholders, which swapped nearly $800 million in debt for equity ownership of the business, while leaving more than $2 billion of debt outstanding.

Spirit recently said it is pulling out of 11 cities and scrapping plans to add service to one more.

“Unfortunately, the industry-wide headwinds that preceded the Prior Chapter 11 Cases did not abate; rather, they intensified,” Chief Financial Officer Fred Cromer wrote in a court filing over the weekend. Instead of the $252 million in profit Spirit had projected for 2025, it reported in August that it had lost more than $256 million since mid-March.

Spirit had started to warn of its dire straits last month and was scrambling to bolster its cash balances. It drew down $275 million on its revolving credit facility and completed a series of sale-leaseback transactions in July and August that brought in approximately $250 million.

Then last week, AerCap, Spirit’s largest lessor, notified the carrier it was terminating leases for 36 planes scheduled for delivery in the coming years, and said Spirit was also in default on more than three dozen planes already in its fleet.

Worried that the disclosure of the notices would panic other creditors, the airline decided it had no choice but to file for chapter 11 bankruptcy protection again.

Spirit denied that it had defaulted on any of the leases. It said it is negotiating with AerCap to resolve the issue and is prepared to litigate the matter. An AerCap representative didn’t respond to requests for comment.

The company is burning through cash fast. Spirit disclosed a projection showing that it expects to burn $179 million for the first month of the bankruptcy case. Cromer said in court papers that the airline is continuing to work with certain bondholders on an agreement that would allow access to “significant additional liquidity.”

Spirit has said this time will be different.

In a bankruptcy court appearance Tuesday, Spirit lawyer Marshall Huebner characterized the recent filing as “really Spirit’s first chapter 11, not its second.” Spirit intends to use the powers of the bankruptcy code to walk away from certain contracts, shrink its aircraft fleet and reduce its operating costs, Huebner said in court.

Once the process is complete, “Spirit will once again be the disruptive maverick that has long challenged—and changed—the U.S. aviation industry,” Cromer wrote.

Write to Alison Sider at alison.sider@wsj.com and Alexander Gladstone at alexander.gladstone@wsj.com

The court allowed Singh’s application, but directed him to return to India and be present for the next date of the trial — September 24.

Singh, who was the first accused to have been granted bail, was earlier directed by the court to surrender his passport before the Central Bureau of Investigation (CBI), which is investigating the case and not to travel abroad as one of the conditions of his bail.

Last month Singh had sought permission from the Panaji district and sessions court to travel to Indonesia for two weeks while also undertaking to return back to India by September 23, the day before the next date of hearing.

“In view of the itinerary given by accused No 2, I am of the opinion that permission can be granted to the accused No 2 to travel abroad,” sessions judge Irshad Aga, said.

Singh along with prime accused Sudhir Pal Sangvan are accused in the murder of the BJP leader on August 22. Phogat, died allegedly due to an overdose of an “obnoxious chemical” suspected to be MDMA that was allegedly mixed with a drink and forcibly given to her during an evening out at a nightclub at Anjuna in north Goa.

The case was initially registered as an “unnatural death” after she was declared dead at the St Anthony’s Hospital at Anjuna in Goa, but subsequently registered as murder based on a complaint filed by her brother Rinku Dhaka, who accused Sudhir Sangvan, the prime accused, who was also her personal assistant of being responsible for her death.

Following an uproar, the case was handed over to the CBI.

Earlier, on account of the trial being prolonged, the court had allowed both the accused to travel outside the state (Goa) and visit their native place in Haryana and relaxed the bail condition that stated they were not to leave the state.

Singh submitted that he and his wife intend to travel to Kuta from September 9 to September 13. From Kuta, they will travel to Canggu for four days till September 17 and thereafter, they will travel by road to Uluwatu and stay there till September 22. The accused submitted that they will return to India on September 23.