The hijack attempt is prevented on board a Malaysia Airlines flight out of Melbourne.

The 25-year-old man who tried to break into the cockpit and threatened to blow up the Malaysia Airlines flight is the latest in a string of people who see planes as the ultimate target.

Despite increased security measures, terrorists continue to develop technology and the authorities are scrambling to keep up. “There’s still a possibility someone could repeat the 9/11 scenario, break into a cockpit and hijack a plane,” Deakin University counter-terrorism researcher Greg Barton told news.com.au.

Everything changed after 9/11. Pictured, first responders at the Pentagon after American Airlines Flight 77 crashed into the building. Picture: AFPSource:AFP

Before 9/11, most plane hijackings were carried out with the intention of diverting an aircraft to a new location. Bombs were typically planted by people who were not on the flight, as was the case when Pan Am Flight 103 was brought down in 1988 over Scotland by an explosive device apparently concealed in a radio in an unaccompanied suitcase. The Lockerbie bombing killed all 243 passengers and 16 crew members on board, as well as 11 residents on the ground.

Checks were introduced to ensure the owners of every piece of luggage were on board and improve scans. But the Twin Towers attack changed everything. “The logic was that people wouldn’t blow themselves up. Now that logic doesn’t apply,” said Professor Barton. “You could hijack a plane to turn it into a weapon for a suicide mission.”

A laptop smuggled aboard a Daallo Airlines plane flying from Mogadishu in Somalia to Djibouti exploded at a window seat. Picture: VOASource:Supplied

FROM SUITCASE BOMBS TO THE ‘MOTHER OF SATAN’

After hijackings became a regular occurrence in the 1970s and 1980s, cockpit doors were locked and armed, weapons checks introduced and new rules established for when flight attendants could come and go.

Following the tragedy of September 11, 2001, such security measures were vastly expanded.

As explosive devices became smaller, concerns switched to cabin luggage, with items swabbed for trace chemicals and scans developed specifically for laptops and electronics and for high-density items such as guns.

Attempts to use nitroglycerine led to 2006’s new rules banning containers holding more than 100ml of liquid in cabin luggage.

Terrorists then developed harder to detect homemade bombs known as TATP or “mother of Satan” that rely on widely accessible industrial chemicals including acetone peroxide. These were used in the 2005 London bombings, by “shoe bomber” Richard Reid, in the November 2015 Paris attacks, the 2016 Brussels bombings and now in Manchester.

In 2015, Islamic State published an image of a soft drink can with what appeared to be a detonator and a switch, claiming the crude device had been used to bring down a Russian MetroJet plane over the Sinai Peninsula. The explosion killed all 217 passengers and seven crew members.

A piece of wreckage of Russian MetroJet Airbus A321 at the site of the crash in Sinai, Egypt, that killed all 224 people on board. Picture: EPA/Maxim Grigoriev / Russian Emergency MinistrySource:AAP

On February 2, 2016, a laptop smuggled aboard a Daallo Airlines plane flying from Mogadishu to Djibouti exploded at a window seat, blasting open a huge hole and ejecting the man authorities believe brought the bomb aboard. The plane was well below the cruising altitude where a sudden decompression would have been worse, and pilots were able to return to Mogadishu safely.

The military has become increasingly worried about the ability of terror groups to smuggle bombs on to planes, several US officials told CNN, based on intelligence from al-Qaeda and IS.

“Evaluated intelligence indicates that terrorist groups continue to target commercial aviation, to include smuggling explosive devices in electronics,” the Department of Homeland Security told CNN in March.

Metropolitan State University aerospace professor Jeffrey Price told Bloomberg: “There’s been, for about four years now, an articulated threat that people will try to smuggle bombs in laptops.”

“They’ve been building very thin explosives,” said security consultant John Halinski, a former deputy administrator at the US Transportation Security Administration. “They are so thin the X-ray machines can’t see them.”

“It’s real,” Homeland Security Secretary John Kelly said of the intelligence in an April 5 testimony to the Senate Committee on Homeland Security and Governmental Affairs. “I think it’s getting realer, so to speak.

‘HAIR-RAISING’ EVIDENCE OF THREAT

With concerns over security at some airports, a ban on laptops and tablets in the cabin was introduced on flights into the US from eight different countries in March and looks set to expand globally. The UK has introduced a similar rule for planes flying from six countries.

The intelligence that contributed to the ban was specific, credible and reliable, three officials told CNN. One called it “hair-raising.”

The FBI said it revealed laptop bombs would now be far more difficult for scans to detect, with bombmakers now sophisticated enough to hide homemade explosives in laptops that can function long enough to get past screeners.

Bombmakers have developed technology that means a small, innocent-looking battery or hard drive can be an explosive, with the Manchester bomber carrying a relatively small backpack that was able to kill 21 people and injure 59, while the 25-year-old on flight MH128 was reportedly carrying a large, black, metallic object.

Al-Qaeda has the greatest expertise, thanks to master bombmaker Ibrahim al Asiri, who is thought to have shared his knowledge with other groups.

While moving a bomb into the hold rather than the cabin isn’t totally safe, terrorists would not be able to ensure it was next to the fuselage and other luggage might contain the impact.

It was the laptop ban that triggered controversy for Donald Trump when The Washington Post reported he had revealed classified details of the aviation threat to Russia. National Security Adviser H.R. McMaster denied the President had revealed intelligence sources.

The 9/11 tragedy led to a massive expansion in security measures. Picture: AFPSource:AFP

WHY TERRORISTS LOVE PLANES

While hijacking or blowing up carefully guarded planes is far harder than attacking a “soft target” like a public space, it holds lasting glamour for prospective terrorists.

“There’s always been a desire for terror groups to bring down planes in flight,” said Prof Barton. “We’ve had some spectacular examples. Lockerbie was one of those tragedies.”

The MetroJet killings demonstrate what is known as “attack utility”, or where an attack will have the greatest impact, CNN reports. It’s not just about body count but maximising the damage to society and the economy.

The al-Qaeda downing of a UPS cargo plane after takeoff from Dubai airport in 2010 and a bomb disguised as a printer cartridge discovered at Britain’s East Midlands Airport are examples of how terror groups hurt nations’ finances by forcing them to spend more and more on aviation security.

Osama bin Laden noted that 9/11 was intended to cause economic harm and trigger reactionary spending and the 2004 Madrid bombing and the 2005 London bombings both drove down those countries’ respective stock markets. After the Charlie Hebdo attacks in Paris, there was widespread cancellation of reservations at restaurants, bars and hotels.

Other challenges include weeding out the airport insiders — baggage handlers, flight attendants and even pilots — who might assist in a terror attack. There was particular concern about explosive devices placed next to fuselage.

Experts have suggested employee security screening and regular background checks, at great expense.

These days, everyone is a suspect. And that’s what the terrorists want.