A helicopter trip to a hospital may not be the only shock a patient faces after a bad accident. The next one could hit when the bill arrives.

Rides in so-called air ambulances can lead to bills of more than $20,000 depending on a person’s coverage, and insurance experts say big invoices are becoming more common as costs rise and coverage shifts.

Air ambulances transport around 400,000 people each year in the U.S., according to industry estimates. Most trips are from one hospital to another. But they also play a vital role in getting seriously injured or ill people fast help during what doctors call “the golden hour” — the initial window after an accident when a patient’s chances for recovery are better. Here’s a deeper look at the issue:

A SPIRALING EXPENSE

Median prices for helicopter air ambulance services doubled from around $15,000 to about $30,000 from 2010 to 2014, according to a U.S. Government Accountability Office report last year.

Patients with private insurance can get stuck with most of that bill if the helicopter that picks them up is not in their coverage network. In those cases, the air ambulance company can bill the patient for the leftover balance after the insurer pays part of it. The GAO report said it was unclear how often patients are billed like this.

The main reason patient costs are rising is because the expense of running air ambulances has more than doubled in the past decade, but reimbursement from the government-funded Medicare program hasn’t changed, said Blair Beggan, a spokeswoman with the trade group Association of Air Medical Services. She added that Medicare reimburses about 58 cents for every dollar air ambulance companies spend transporting patients, and some commercial insurers have been reducing their reimbursement to bring it closer Medicare rates.

That, Beggan said, can force air ambulance companies to leave insurer networks.

The GAO report noted that air ambulance providers don’t face the type of competition that could restrain costs. Patients have little control over the decision to call for an air transport and can’t avoid companies that may be too expensive and outside their insurance network.

SOME PREVENTIVE MEASURES

There are limited safeguards for avoiding a big bill.

Some air ambulance companies will sell memberships that cost less than $100 a year. Those will take care of flight expenses, but they often apply to only one company. A patient still might wind up stuck with a big bill if a competing company responds to the call.

Some insurers will offer riders to employer-sponsored health coverage that allow workers to pay a few extra bucks a month in order to have any air ambulance flight covered as though it were in their network.

HANDLING THE BIG BILL

Don’t panic if a five-figure invoice arrives in your mailbox from an air ambulance company. There may be a way to resolve it, or at least knock down the amount.

Start by contacting your insurer to make sure the claim has been processed correctly. Some air ambulance companies provide patient advocates who do this.

An insurance broker also may be able to double-check the claim’s accuracy or check for any potential discounts.

An air ambulance company will sometimes knock 10 percent off the bill without asking the customer to prove that it would be a financial hardship, said Marietta, Ohio, broker Kristen First. Even deeper reductions may be available for patients who produce tax filings, check stubs or other items showing how much of a strain the bill would impose.

First said her agency had a customer do that, and the air ambulance provider chopped a bill of about $25,000 down to $3,500.

(AP)