(CNN) -- "Your flight has been delayed due to a mechanical problem" -- it is something a passenger never really wants to hear especially during Thanksgiving week.
More than 24 million passengers are expected to fly in the U.S. during the Thanksgiving holiday which runs from November 16 through the 27.
CNN went behind the scenes with maintenance crews at United Airlines at its base in Houston to find out how they work to keep planes flying safe and on time. More than 600 flights will go through Houston this Wednesday alone.
Before any flight takes off, a mechanic examines the plane to make sure there is nothing wrong.
"We do just a walk around inspection, then we go upstairs and check the gauges and the log books and if there is anything broken we will fix it at that point," United Airlines technician Michael Baumgarten told CNN as he inspected a 737 just arrived from Guatemala. "We look at all the critical things -- anything at all broken, leaking, worn out. Any problems at all."
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He peers into the engine, sticks his head into the wheel wells and eyeballs the wings.
"After looking at a million of them you will pretty much recognize anything at all out of place," he said.
When a problem is detected in the air, a pilot can enter details of the issue into the plane's in-flight computer so maintenance can be standing by when it lands to make a quick fix.
Often this work can be as simple as a broken in-flight entertainment system or just a seat cushion wet from a spilled drink which can be quickly replaced without causing a delay.
If repair work requires a long time, planes are moved to the hangar area.
During CNN's visit, the airline's new 787 Dreamliner was there so teams could check out a couple of the systems on a layover.
"We are kind of getting to know it," maintenance supervisor Larry Thomson said standing outside the cockpit. "It's very electronic, a lot more than any airplane we've ever had before. The systems are completely different than any airplane we ever had."
In the passenger compartment, a computer by the door can show technicians on board problems with a simple
"We could run a test on all the monitors on the airplane and it would tell us if there is a problem," Darrell Miller said.
He is the manager of United Airlines technical operations and has spent more than 25 years working his way up with Continental and United.
"It has changed a lot from pushing all of the light switches on every light to see if it works," he said.
Inside the hangar sits a 737 in the midst of a brake job. The airline is installing new carbon fiber brakes which will lighten the load and save the airline money.
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In a neighboring building, a 757 is partially disassembled and surrounded by scaffolding for a major overhaul.
"They get deep into it," Miller pointed out. "This is probably the highest level of maintenance you would do," he said.
"They will open the airplane up, inspect everything, replace a lot of components, lubricate everything and put it back together."
Planes go into the hangar for these massive month-long overhauls every four or five years.
"When these guys get it done, it will be in excellent shape," he said.
Though much of United's maintenance is done in Houston and San Francisco, there are crews at 45 other airports around the world to work on the airline's planes.
In some cases they even have contracts to do work on competitors' aircraft.
There are about 8,000 United mechanics worldwide, as well as 2,000 other members of its Tech Ops division, including engineers, maintenance planners and inspectors.
Their goal, they say, is to make sure their planes are safe and they get you there on time and this busy holiday season is no different
"It's the same responsibility as it is every day," Baumgarten told CNN. "Our job doesn't change if a plane is going to go one mile, empty, full -- our job is exactly the same."
"Every plane has to go out safe."
By Aaron Cooper, CNN
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