Not long after several planes were hijacked and used to wreak devastation on downtown New York and Washington, DC, a quarter of a century ago, air travel for millions of people all over the world changed beyond recognition – forever.
Two of the planes, hijacked by men linked to al-Qaeda, were flown into the Twin Towers at the World Trade Centre at the south end of Manhattan Island in New York City, causing the buildings to collapse and killing nearly 3,000 people.
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A third hit the Pentagon, the building in Washington that houses the United States Department of Defense, while a fourth, believed to be headed towards the White House, crashed into an empty field in Pennsylvania after passengers on board wrested control of the aircraft from the hijackers.
It was the deadliest terrorist attack in US history, and all the planes had been boarded and seized with relative ease by the hijackers.
Here’s a look at how life for air passengers has changed since then.
Across the US, all air traffic was immediately grounded. Canada closed its airspace but exempted military, police and humanitarian flights, according to a government document.
In other countries, airports were closed and flights to the US were cancelled, causing many people to be stranded for days.
Canada reopened its airspace in stages, with domestic flights allowed to resume on September 12, followed by international flights a day later, and final restrictions removed the day after.
On September 13, the US also reopened its airspace.
What new travel rules came into place afterwards?
ID and baggage checks
Before September 2001, travellers could turn up for a domestic flight in the US and walk straight to their gate without showing identification, while their friends and family were permitted to accompany them to the gate to say goodbye at most US airports.
In some instances, travellers were able to transfer from US domestic flights to international flights without going through any further security checks, either.
That all changed immediately after September 11, and, in November 2001, then-US President George Bush signed the Aviation and Transportation Security Act (ATSA) into law, requiring all passengers and their baggage to undergo checks by federal officials. The act created the Transportation Security Administration (TSA).
Armed marshals and reinforced cockpits
The Federal Air Marshal Service was expanded, with more armed air marshals placed on flights. Cockpit doors, which had often been unlocked during flights before, were required by law to be reinforced, fitted with bulletproof materials, and remain locked from the inside to keep potential attackers out.
Other countries swiftly adopted the new standard for reinforced cockpits, with British airline carrier Virgin Airways becoming one of the first to announce the measure in October 2001.
Now, reinforced cockpit doors are standard on commercial airlines, although not all are bulletproof.
Knives
Immediately after 9/11, knives and box cutters were banned from carry-on baggage. Before the attack, the Federal Aviation Administration had allowed passengers to carry knives which were less than 10cm (4in) long on board the aircraft.
Shoe checks
In December 2001, British-born Richard Reid attempted to detonate explosives he had hidden in his shoe on an American Airlines flight from Paris to Miami.
He was thwarted when other passengers on board restrained him, but the incident prompted the TSA and some airlines worldwide to begin asking passengers to remove their shoes for security screening on a voluntary basis.
In 2006, the TSA made shoe checks mandatory.
Pilots with handguns
In 2003, the first pilots were certified under the US Federal Flight Deck Officer programme to carry handguns if they wanted to after undergoing training to defend commercial aircraft.
Limits on liquids
In 2006, United Kingdom authorities uncovered and foiled a plot to detonate liquid explosives on board aircraft travelling from London to various US and Canadian cities.
According to the UK government at the time, the planned attacks could have caused more deaths than September 11.
As a result, the US banned all liquids, gels and aerosols from carry-on luggage. In September, it relaxed the rule to allow liquids, but only 100ml (3.4oz), and they had to fit in a small clear bag to allow security officials to view them.
Full-body scanners
In 2009, on a flight from Amsterdam to Detroit, a man named Umar Farouk Abdulmutallab attempted to detonate a bomb that he had hidden in his underwear. Al-Qaeda in the Arabian Peninsula (AQAP), a group based in Yemen, claimed it was behind the attempted attack.
Although the attack failed, the TSA began installing full-body scanners that use advanced imaging technology to detect anything hidden under clothes.
These scanners are now used across Europe, Japan, the UK and other countries.
Facial recognition software and electronics checks
In 2017, some airlines began trials of facial recognition software to allow passengers’ faces to serve as their boarding passes. The trials later became part of a new biometric boarding system, which is used at major airports internationally. The same year, rules were implemented requiring travellers to place electronics larger than a mobile phone into security trays for checking in X-ray machines.
How has this affected air passengers?
With more thorough baggage and security checks than before, passengers now spend more time in the airport, meaning journeys take longer.
According to a 2007 research journal by Alexander G de Barros and David D Tomber, a few years after the main measures were first implemented, the added screening protocols had made the processing rate at passenger screening points drop from “500 to 600 passengers per hour per lane before September 2001, to 100 to 150 passengers” after 9/11.
Moreover, passenger numbers in North America fell by up to 30 percent straight after September 2001, according to a research journal in 2003 on ScienceDirect, a platform that provides access to peer-reviewed reports.
Passenger footfall steadily increased, however, as people adapted to the new way of travelling. By 2005, it had reached 735.1 million international and domestic travellers boarding planes, surpassing pre-9/11 levels in 2000 of 665.4 million, according to the US Bureau of Transportation Statistics.
Post-9/11 security screening led to more people being subjected to questioning and searches at airports, however.
In 2007, the US Pew Research Centre think tank found that 30 percent of the 1,000 people they interviewed had been singled out by airport security because they were Muslim.
While visas were still being processed, security checks were far stricter.
In 2009, the Electronic System for Travel Authorisation (ESTA) was implemented for countries that participated in the waiver programme. This allowed the US to carry out background checks before passengers boarded their flights.
Which restrictions have been eased over time, and which have remained in place?
Some rules and restrictions have been relaxed, but others remain.
Those still in place include:
- Reinforced and bulletproof cockpits still exist worldwide for commercial airlines. Older planes have also been adapted for this new rule.
- X-ray-checked baggage screening. While baggage was scanned pre-9/11, it became much more extensive following the attack.
- Passenger identity screening with checks against government databases.
- Access to boarding gates restricted to passengers only.
- Screening of passengers at a physical security checkpoint – now often both before reaching the departure gate as well as at the gate itself.
- Prohibiting dangerous objects such as knives in carry-on luggage.
Those which have been relaxed include:
- 100ml liquids rule – while this still exists in the US, in other countries such as the UK, the rule has been relaxed to allow up to two litres (68oz) of liquids in hand luggage.
- Shoe removal – in the US, this rule was relaxed last year, with an exception for steel-toe boots, as they can impact the scanners and have to go through an X-ray machine along with bags. Most European airports also allow travellers to keep their shoes on unless they trigger scanners.
- On Wednesday this week, TSA announced that a number of people without plane tickets will be allowed to pass through security and go to gates to see off loved ones if they have registered on a PreCheck programme.
