SOUTH PORTLAND — Almost every day, Sarah Wilcox and her daughter Morgan, who’s 5, pull into a dirt parking lot off Aviation Boulevard to watch the planes landing and taking off at the Portland International Jetport.

Morgan said she likes watching the big planes the best.

“It keeps her entertained,” said her mother.

The two South Portland residents are among the regulars at the lot, where a dozen or so vehicles can be found during the airport’s busy hours. Known as plane spotters in the aviation community, these enthusiasts say a front-row seat overlooking the runways at the jetport is more exciting than it may look to the uninitiated. They say their hobby is like bird watching, only it focuses on manmade, rather than feather-aided, flight.

Although the jetport is Maine’s busiest airport, it’s a far cry from the world’s great aviation hubs such as Chicago’s O’Hare and London’s Heathrow airports. Still, it has its charms, say those who like to keep a close eye on it.

At noon on Friday, the parking lot was filled with the sounds of chirping crickets while monarch butterflies flittered about, between the ear-splitting roars of the landings and takeoffs.

“Watching the comings and goings of the planes and even the ground crews, I just enjoy it,” said Jake Carr of Scarborough, who stops by once a week or so to eat his lunch.

The parking lot, at the junction of Westbrook Street and Jetport Plaza Road, opened in the fall of 2009. People used to park on the airport access roads, but police began to crack down after the Sept. 11 terrorist attacks.

Paul Bradbury, the jetport manager, said he realized that it made sense to keep the jetport’s fan base happy and found a place for plane spotters to gather. A plane spotter’s guide to the various types of airplanes that use the airport was installed, and the crowds descended.

The top deck of the jetport parking garage is another great plane-spotting site, say enthusiasts, but it costs money if you drive in.

Kevin Porter of Gorham, who founded an online Yahoo group for Portland jetport enthusiasts, said not all airports are as welcoming to plane spotters.

“Orlando hates spotters,” said Porter, a senior at Embry-Riddle Aeronautical University in Florida, where he is studying to become a crash investigator.

Porter’s love of aviation was sparked when he was in high school by a career program at the jetport. Now, he’s a hard-core spotter. He owns a radio that enables him to listen in on the chatter between flight crews and air traffic controllers in the tower.

Adrian Dowling of South Portland said his first love was trains, but he switched to airplanes a few years ago, after moving near the jetport. He swings by the parking lot once or twice a week, and if he sees something unusual or interesting, he will alert other spotters in the Yahoo jetport group.

“It started out as an annoyance because of how loud they are, but it evolved into a fascination,” said Dowling of the aircraft.

Dowling can identify some airplanes by their sound alone, a skill he attributes to a musical education. He said his favorite plane is the MD 88, an aircraft used for Delta flights that holds his grudging respect.

“It wakes me up every morning at a time that is really earlier than I prefer. It is dramatic and impressive. You feel it in your chest, your feet, and it makes the ground shake,” said Dowling.

Others say watching the jetport makes them feel connected to the world. Scott Andrews of Portland, a writer, goes to the parking lot to work. He said it offers him an escape from the confines of his home office.

“This is a place where something is happening, but not too distracting to work,” Andrews said.

Mary Cyr, a lifelong South Portland resident, grew up watching planes on the access roads. She recently rediscovered the pleasure after taking a job near the jetport. Cyr didn’t know about the parking lot until police pointed it out after rousting her from her usual spot in a nearby cul-de-sac.

She said she gets a vicarious thrill watching planes filled with people bound for other places, and there is always an element of danger.

“It’s kind of peaceful but exciting,” said Cyr.

Being a plane spotter isn’t all fun. Porter, who photographs planes, said that before the parking lot was built, he had regular run-ins with police who responded to reports from passers-by who were suspicious about his intentions.

“But the airport administration understood I was spotting,” Porter said.

Dowling said he is acutely aware that some people consider plane spotting a little weird and very geeky. But he failed to see the appeal of more conventional hobbies, such as stamp collecting.

“My eyes glazed over,” he said. “It was like eating dried oatmeal.”