(CNN) As travelers around the world absorb the implications of Tuesday morning's terror attacks on the Brussels Airport and Maelbeek metro station, there are calls to improve airport security to prevent future attacks.
There are already more police and military personnel at major international airports in Europe, the United States and around the world in response to the attacks, and travelers are being told to arrive earlier because of increased pre-flight security.
That's a typical response after a terrorist attack, says aviation security expert Richard Bloom. But that's not the only answer to preventing future attacks.
Detecting threats well before they arrive at the airport is key.
"The United States and Israel have two of the best aviation security operations in the world," says Bloom, who is Embry-Riddle Aeronautical University's chief academic officer and director of terrorism, intelligence and security studies.
"They engage in intelligence gathering operations and identify people who are a threat way before they get anywhere near the airport," he says. "The farther away you handle it, neutralizing the threat, the better off you are."
Airport security isn't terribly complicated, says Bloom, who consults with airports about security. He advises clients that they need to collect and analyze data about possible threats, study their facility's vulnerabilities and figure out the risks to the airport.
Based on that risk and available funds, government and airport officials can decide what to spend on human and technological security options.
The gold standard for airport security is Israel, which exists in conflict with many of its neighbors in the Middle East. As a result, its airport screening process is especially rigorous, starting when travelers buy plane tickets to and from the country.
In addition to the intelligence-gathering and passenger scrutiny that travelers can't see, there's a security check on the road leading into Israel's largest airport, Tel Aviv Ben Gurion International Airport.
There's another check before travelers enter the terminal, and then they go through the pre-flight security screening that's required in airports around the globe.
Yet adopting similar measures in other parts of the world is partly a question of cost and scale.
The Brussels Airport alone handled 23.4 million passengers last year, according to Airports Council International, the global trade representative of airports.
In Israel, about 16.3 million passengers flew into and out of Ben Gurion last year, ACI figures show.
By contrast, some 800 million revenue-paying passengers flew on U.S. carriers last year, according to U.S. government data.
The United States has 485 commercial service airports, says Airports Council International, which represents more than half of them.
That's why bringing Israel's system to the United States would be cost-prohibitive, says aviation security consultant Jeff Price of Leading Edge Strategies.
"If we want to do (in the United States) what Israel does, the cost would be extraordinary," says Price. "Budgets would be as least 10 times higher."
Financial hurdles aren't the only barriers to adopting a more stringent set of visible and invisible layers of airport security.
Critics have accused both Israel and the United States of racial profiling in aviation security procedures.
Last year, Israel's High Court refused to ban racial profiling in a court case brought by the Association for Civil Rights in Israel. The court did leave the door open for ACRI to file a case in the future.
The United States' Transportation Security Administration, established after the September 11, 2001, terrorist attacks, touts its evolution from a "one-size-fits-all security screening approach to a risk-based, intelligence-driven strategy."
Yet that strategy, which includes a Behavior Detection and Analysis program that the agency says is scientifically substantiated, has long been criticized by passengers, security analysts and civil liberties advocates as flawed and discriminatory. The American Civil Liberties Union sued for records related to the program in 2015 to gauge the program's effectiveness.
In Europe, each nation administers its own aviation security with European Union member states and a handful of closely aligned countries operating under overarching rules established by the European Commission in 2002.
Implementation of those standards varies, even within European countries, from airport to airport, says Price, declining to name specific airports.
In the meantime, experts predict tighter security measures at airports worldwide.
Ordinary travelers likely won't notice most of them, such as increased intelligence-gathering, more explosives detection devices and random security screenings of flight crews and airport personnel.
Brendan Koerner, a contributing editor at Wired and the author of "The Skies Belong to Us," which details the hijackings of the 1960s and 1970s that led to increased security at U.S. airports, expects "a wholesale reconsideration of where the security curtain, so to speak, begins in airports."
"As of right now, of course, you can pull your car right up the curb at any major airport, just feet away from the doors that lead to the ticketing areas," says Koerner.
He expects more barriers between the drop-off areas and main doors to reduce the chances of improvised explosive device attacks via vehicle.
But there's just no way to prevent all attacks, the experts say.
"I'm not sure how much more we can ramp up security without seriously infringing on the freedoms that are so integral to our lives," says Koerner.
"An armed guard at every door throughout the world? That seems unworkable and, to be frank, precisely the sort of overreaction that the Islamic State wants to invite."
And even that might not prove 100% effective.
"Even when you do everything right, bad things still can happen," Bloom said.