For the last few weeks, in addition to its usual payload of passengers, medicine, and supplies, Alaska Seaplanes has carried some unique cargo: midterm election ballots.

The regional airline is a piece of a complex logistical puzzle that sees Alaskans' ballots cast by mail and in person carried across the vast expanse of America's largest state, which is primarily connected by water and air rather than roads.

This considerable task explains why, a week after most US states knew their results in the midterms - in which the Democrats won back both chambers of Congress from the Republicans - Alaskans are still waiting for the Senate race to be called.

The victor in this close contest between the incumbent Republican Dan Sullivan and his Democratic challenger, former congresswoman Mary Peltola, could remain unknown until 18 November, when officials expect to have counted all eligible ballots.

"We do feel a sense of pride of making sure we do the job right - the really complicated job of getting all these ballots across thousands of miles in Alaska," Andy Kline, the marketing director of Alaska Seaplanes, which serves the south-eastern part of the state, told the BBC.

"We feel like we're part of the last leg of that journey of those ballots."

Some precincts in Alaska are able to communicate their initial results to centralised election offices on election night, allowing state officials and news outlets to report some preliminary vote tallies.

But it takes some time for the full picture of how people have voted to emerge.

As well as having the logistical challenge of counting votes from across a state more than six times the size of the UK, there is a delay waiting for mail ballots to arrive, says Charles Stewart, an election expert at the Massachusetts Institute of Technology.

These ballots can arrive up to 10 days later, or 15 days for overseas voters, if postmarked by election day.

Stewart said that election officials had "chosen to err on the side of getting it right rather than a rush to report the second and third tranches of ballots that get counted".

Regardless of whether ballots were cast in person or by mail, all of them eventually wind up in the state capital of Juneau – which is only reachable by plane or boat – for scanning and counting.

While more urban districts can get their materials on a plane late on election night, it takes longer for smaller or more remote parts of Alaska.

In some places, "you get someone who's basically running the election for their family and their neighbours because it's such a small village", says Scott Kendall, an election lawyer who previously worked on two campaigns for Alaska's other Republican senator, Lisa Murkowski.

In these smaller areas, ballots are sealed up in special envelopes or containers and sent it through the mail - which is where companies like Alaska Seaplanes comes in.

Ballots are put on the planes and sent to Juneau, where they then get dropped at the post office and delivered.

"It's part of our daily routine, just another couple of boxes," Kline said.