Before a small plane crashed into power lines and tower in Maryland, an air traffic controller warned pilot his altitude reading was too low

(CNN) -- Moments before a small private airplane crashed into power lines in Maryland on Sunday evening, air traffic controllers urgently warned the pilot that the aircraft was flying too low, according to archived recordings.

"N201RF, if you hear this transmission, low altitude alert," said a controller from Potomac Terminal Radar Approach Control in the transmission recording, accessed from LiveATC.net.

The controller repeated the current air pressure to give the pilot a more accurate read of his height above sea level.

Earlier in the flight, the pilot apparently missed assigned directives from the controller who explained he was worried the single-engine Mooney airplane would stray into the path of commercial flights approaching nearby Washington Dulles International Airport.

Air traffic control recordings detail that the pilot was cleared for an approach to land at Montgomery County Airpark in Gaithersburg by sole reference to instruments in the airplane, not outside visual cues. The weather at the time of the crash was reported as poor with low clouds and bad visibility.

The pilot was identified by Maryland State Police as Patrick Merkle, 65, of Washington, DC. The passenger is Jan Williams, 66, of Louisiana, state police said in a news release.

The two were stuck in the plane for nearly seven hours after it crashed into power lines and a utility tower in Montgomery County, Maryland, according to fire chief Scott Goldstein.

Both were taken to the hospital with serious injuries, including orthopedic and trauma injuries from the crash and hypothermia, Goldstein said. At a later news conference he said their conditions had improved and one person had been released.

The rescue began at 5:30 p.m. when crews responded to reports of a small airplane that had flown into the power lines, according to Pete Piringer, chief spokesperson for Montgomery County Fire & Rescue Service.

When units arrived at the scene, they found a small plane "embedded" in the tower about 100 feet above the ground after striking the lines from another, nearby tower, according to officials.

"The aircraft did strike the power lines of the north tower (while on approach to an airport) before it then collided with and became embedded in the structure of the south tower," Goldstein said Monday.

Fire authorities talked with the pilot and passenger throughout the rescue and nearby roads were closed, according to officials. The crash scene is about 4 miles northwest of the Montgomery County Airpark, state police said.

Rescuers had to wait for the tower to be "grounded or bonded" before they could get to the duo in the plane, Goldstein told reporters Sunday evening. They were also concerned the plane might shift, but it didn't as it seems it was held in place by the tower, Piringer added Monday.

It involved crews ascending to put clamps or cables onto the wires to make sure there was no static electricity or residual power, the chief said. The airplane also needed to be secured to the tower structure, he said. Foggy weather conditions made matters more complicated, he added.

A utility contractor finished grounding power lines near the plane at 11:30 p.m., Goldstein said, and the contractor helped rescue crews secure the plane within the next 45 minutes. .

Crews used a cherry picker -- in this case, a truck with a 170-foot crane with a platform to lift humans -- to reach the people trapped, according to photos tweeted by Piringer.

The first person was removed from the plane at 12:25 a.m. and the second person was removed about 10 minutes later, Goldstein said.

At around 4 a.m. Monday, the plane was removed from the tower and placed on the ground, Piringer tweeted.

About 120,000 customers were without power Sunday evening following the crash, but all impacted customers had their power restored as of early Monday, according to the Pepco utility company, which provides electric service to roughly 894,000 homes and businesses in Washington, DC, and surrounding areas in Maryland. Montgomery County is just north of Washington, DC.

Schools in Montgomery County will be closed Monday due to power outages, district officials said Sunday night.

The district earlier said more than 40 schools in the Montgomery County Public Schools system and six central offices were without power, affecting services such as maintenance, buses and food service.

Two hospitals, MedStar Montgomery Medical Center and Holy Cross Hospital, operated in a limited capacity Sunday evening due to the power outage, Goldstein said.

Officials from the Federal Aviation Administration and leadership from Maryland State Police were on scene, Goldstein said Sunday night. The FAA put an aircraft restriction in place during rescue efforts, state police said.

The FAA said the aircraft departed from Westchester County Airport in New York. The agency will assist the National Transportation Safety Board, which identified the plane's model as a Mooney M20J, with its investigation.

William Smouse, who lives about a mile from where the crash took place, told CNN affiliate WJLA on Sunday evening he was going out to dinner with his son when he saw "two big flashes" and then fire engines driving by.

Smouse said the incident was "pretty scary" and his house is located in an area where planes and jets often pass through.

"I think about it a lot, where they come in, and, literally, they are like 200 or 300 feet over us," he said.

By Emma Tucker, Rashard Rose, Pete Muntean and Nicky Robertson, CNN   

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