The elevators used to transport visitors 750 feet underground at Carlsbad Caverns National Park are back in service after undergoing routine maintenance throughout the last several days.

The two elevators will return to use a day earlier than planned on Friday, should a morning inspection go well, said park spokeswoman Valerie Gohlke.

All 16 of the steel cables used to raise and lower the elevators were replaced as part of the $118,000 maintenance project.

On Wednesday, the park announced the elevators would be back in service on Thursday. However, it was discovered on Thursday morning that the steel cables had stretched more than anticipated and adjustments were needed, Gohlke said.

The maintenance work began Feb. 6. The elevators were brought back online Feb. 11 and 12 before work resumed on Monday.

The cables must be replaced every 5 to 7 years.

A mandatory annual inspection of the steel-lined hoist way at the end of the month will take      them out of service for another couple days. Those dates have not yet been confirmed.

Trouble with the elevators began in November 2015 when one of the park’s two passenger elevators stopped working at the bottom of the shaft when a component inside its motor broke down.

Due to the magnitude of the repairs needed, the freight elevators, which were also out of service at the point, were repaired and back in use by May 2016.

Park officials originally estimated the passenger elevators would be repaired by March 2016, but that date has been pushed back several times.

Currently, the park hopes to begin construction on the passenger elevators in May and have a completely renovated and modernized pair of passenger elevators ready for use by May 2018.

That project will involve replacement of all machinery on both passenger elevators, including the cars, motors and counterweights.

Funding to repair the passenger elevators, installed 60 years ago, was awarded last year.

Work on the freight elevators will involve the replacement of steel guide rails in the shaft, which are 85 years old.