Delays and cancellations at Denver International Airport are sometimes unavoidable because of winter or summer storms, or even global technology outages.

So what do airlines offer passengers for the inconvenience?

All U.S. airlines are required to follow through on promises made in customer service plans and to refund travelers if their flights are canceled or “significantly delayed,” according to the U.S. Department of Transportation.

“Each airline has its own policies about what it will do for delayed or canceled passengers,” federal transportation officials said. “If an airline has made a commitment to provide a particular service or compensation, then the Department can hold the airline accountable.”

However, airlines only have to adhere to their customer service plans when the delays and cancellations are “controllable” — such as for maintenance or crew problems, cabin cleaning, baggage loading and fueling, according to federal transportation officials.

When flights are delayed or canceled because of the weather, disasters or air traffic control conditions, airlines do not have to honor any promises in their customer service plans.

Even if airlines don’t have to follow through on promises of meals and hotels during uncontrollable situations, they still have to follow federal rules surrounding refunds.

If a U.S. airline cancels a flight or significantly delays takeoff — regardless of the reason — airlines are required to refund ticketed passengers if they choose not to accept the alternative offered — such as rebooking on another flight — federal officials said. This includes passengers with nonrefundable tickets.

The DOT has not specifically defined what constitutes a “significant delay,” claiming it depends on the length of the delay, the length of the flight and the passenger’s specific circumstances. Federal transportation officials review delay-based refund claims on a case-by-case basis.

Other federally protected refunds include:

Class of service change: A customer is entitled to a refund if they are involuntarily moved to a lower class of service. For example, if the passenger purchased a first-class ticket and was downgraded to economy class due to an aircraft swap, the consumer is owed the difference in fares.

Optional service fees: A consumer is entitled to a refund of fees paid for an optional service — including baggage fees, seat upgrades or in-flight Wi-Fi — if they were unable to use the optional service because of a flight cancellation, delay or schedule change or if they were involuntarily denied boarding. If passengers purchase an optional service and the amenity does not work or is not available on the flight, they are also entitled to a refund, according to the U.S. DOT.

Baggage fees: A passenger is entitled to a refund if the customer paid a baggage fee and their luggage was lost by the airline.

• Airlines may have different policies to determine when a bag is officially lost. Most airlines will declare a bag lost between five and 14 days after the flight.

• If an airline unreasonably refuses to consider a bag lost after it has been missing for an “unreasonable period of time,” the airline could be subject to enforcement action by the DOT.

• Airlines are also responsible for repairing or reimbursing a passenger for damaged baggage and/or its contents when the damage occurs while the bag is under the airline’s control. When the damage to the bag cannot be repaired, airlines will negotiate a compensation amount based on the value of the bag and its depreciation.

• More information about baggage policies, what airlines can restrict from their policy and how much airlines owe customers for damaged and lost bags is available on the U.S. Department of Transportation’s website.

So, if airlines have to honor their customer service plans, what does each company promise customers?

Southwest

If a flight is canceled and the airline could have prevented it, Southwest will:

• Rebook a passenger on same airline at no additional cost.

• Provide meals, meal cash or meal vouchers for passengers waiting three hours or more for a new flight.

• Offer hotel accommodations and transportation to and from the airport for passengers affected by an overnight cancellation where the next available option isn’t until the next day.

• Give passengers a flight credit or travel voucher when the cancellation results in passengers waiting for a new flight three or more hours past their scheduled departure time.

If a flight is “significantly delayed” — which is determined on a case-by-case basis — passengers have essentially the same options as with cancellations.

“If you ask, we’ll give you a voucher for food at airport vendors who accept our vouchers,” Southwest officials stated. “If there’s no place to use the voucher or no vouchers available, we may honor reasonable requests for reimbursement of meal costs.”

Passengers stranded by extended overnight delays and cancellations also have to ask for hotel lodging and transportation — Southwest officials said the airline won’t announce it, but it will provide accommodations if the situation was caused by something officials “determined was within (the airline’s) control.”

To get reimbursed for meal, hotel and transportation expenses, passengers can fill out the form on Southwest’s website within one year of their flight.

Frontier

If a flight is canceled and the airline could have prevented it, or a flight is significantly delayed, Frontier will:

• Rebook the passenger on the same airline at no additional cost.

• Provide meals, meal cash or meal vouchers for passengers waiting three hours or more for a new flight.

American Airlines

If a flight is canceled and the airline could have prevented it, American Airlines will:

• Rebook the passenger on the same airline or another partner airline at no additional cost.

• Provide meals, meal cash or meal vouchers for passengers waiting three hours or more for a new flight.

• Offer hotel accommodations and transportation to and from the airport for passengers affected by an overnight cancellation where the next available option isn’t until the next day.

If a flight is “significantly delayed” — which is determined on a case-by-case basis — the options are essentially the same as with cancellations.

“If the delay or cancellation is caused by events beyond our control (like weather), you are responsible for your own overnight accommodations, meals and incidental expenses,” airline officials stated.

“If you decide not to fly because of a flight cancellation or a significant delay, you can request a refund for the remaining ticket value and related optional fees.”

Delta

If a flight is canceled and the airline could have prevented it, Delta will:

• Rebook passengers on the same airline or another partner airline at no additional cost.

• Provide meals, meal cash or meal vouchers for passengers waiting three hours or more for a new flight.

• Offer hotel accommodations and transportation to and from the airport for passengers affected by an overnight cancellation where the next available option isn’t until the next day.

If a flight is “significantly delayed” — which is determined on a case-by-case basis — the options are essentially the same as with cancellations.

United

If a flight is canceled and the airline could have prevented it, United will:

• Rebook passengers on the same airline or another partner airline at no additional cost.

• Provide meals, meal cash or meal vouchers for passengers waiting three hours or more for a new flight.

• Offer hotel accommodations and transportation to and from the airport for passengers affected by an overnight cancellation where the next available option isn’t until the next day.

If a flight is “significantly delayed” — which is determined on a case-by-case basis — the options are essentially the same as with cancellations.

United offers refunds in cash, bank orders, bank checks and through electronic funds transfers. They can only give refunds in the form of a travel voucher with the passenger’s written agreement.

For international flights, United Airlines puts delayed and canceled flights into three different categories: flights delayed by two or more hours, flights delayed by five or more hours and flights delayed by at least eight hours or canceled altogether.

If a flight is delayed by at least two hours or a passenger is involuntarily denied boarding on a flight, the airline starts offering compensation, according to United’s Notice of Rights policy, including:

• Meals, meal cash or meal vouchers for passengers waiting three hours or more for a new flight.

• Hotel accommodations and transportation to and from the airport for passengers affected by an overnight cancelation where the next available option isn’t until the next day.

The airline says it may “limit or decline (passengers’) right to care if (the) provision of care would itself cause further delay.”

Once the delay hits five hours, passengers get to choose between two compensation options outlined in the airline’s policy.

• A refund for the full cost of the ticket for the parts of the flight not made and — if the flight “no longer serves any purpose in relation to your original travel plan” — the parts of the journey already flown. If the delay happens during a layover, United is also responsible for providing the earliest possible flight back to your home airport. Or,

• A rescheduled flight under “comparable transport conditions” to your final destination as soon as possible or at a later date that works better for passengers’ schedules. If United offers a flight to an airport nearby — but different than — your original destination, the airline is responsible for covering transportation to or near the original airport.

If the flight is delayed eight hours or canceled, United says passengers may be eligible for monetary compensation, flight vouchers or rewards points.