Why a Boeing 737 Max filter on Kayak spiked in usage for airplane selection

As some of Alaska Airlines' 737 MAX aircraft take flight again on Friday, online travel booking website Kayak has seen an uptick in users who are filtering out the airplane when searching for flights.

Kayak first rolled out its aircraft filter in March 2019, but the company said it saw 15 times the typical use of the tool between Saturday, Jan. 6 and the following Thursday, specifically for 737 MAX planes immediately following the Jan. 5 Alaska Airlines incident, in which a door plug fell off of a 737 MAX 9 aircraft a few minutes after takeoff.

Kayak filter for Boeing 737 Max models

Kayak recently added a capability to its filter for users to specify 737 Max 8 and 737 Max 9 models, which are still in flight, and moved the filter higher on their website's landing page to make the tool more prominent for travelers.

"KAYAK makes it easy for concerned travelers to avoid 737 Max flights. We've increased the prominence of the MAX filter on site. Airlines do often substitute equipment – so travelers should double check before departure," Kayak CEO Steve Hafner told ABC News in an emailed statement.

FAA approves inspection process for Boeing 737 MAX 9 aircraft

Earlier this week, the Federal Aviation Administration (FAA) approved a thorough inspection and maintenance process for the 737 MAX 9 aircraft, which Alaska Airlines said it is ready to perform.

"Each of our aircraft will only return to service once the rigorous inspections are completed and each aircraft is deemed airworthy according to the FAA requirements," a representative for Alaska Airlines said in a written statement to ABC News. "We have 65 737-9 MAX in our fleet. The inspections are expected to take up to 12 hours for each plane."

The first of the airline's 737 MAX 9 aircraft will resume flying commercial service on Friday, the statement said, adding that more planes will be added "as inspections are completed and each aircraft is deemed airworthy."

Alaska Airlines said its maintenance technicians, at the FAA's request, "completed preliminary inspections on 20" of those aircraft, and that data from those inspections was provided to the FAA for further analysis.

"Those findings informed the FAA's final orders for thorough inspections of the door plug on each of our 737-9 MAX aircraft," the airline stated. "We are now ready to implement those final orders."

What happened on Alaska Airlines' Boeing 737 Max 9 flight

After an investigation into the Jan. 5 incident, the National Transportation Safety Board found that the fuselage door plug of Alaska Airlines Flight 1282, which was a Boeing 737 Max 9, fell off a few minutes after the aircraft took off from Portland International Airport. That resulted in a depressurized cabin which exposed passengers to open air at about 16,000 feet above the ground.

No one was seriously injured and the plane made an emergency landing safely.

ABC News' Sam Sweeney contributed to this report.