When United States President Donald Trump flies to Singapore to meet North Korean leader Kim Jong Un, air traffic controllers at Changi Airport will be looking out for not one but two of the American President's official blue-and-white Boeing 747 jets.
The decoy - the one not carrying Mr Trump - will likely fly over the island and land elsewhere, quite possibly at the US Air Force base in Japan.
At Changi Airport, snipers are likely to be stationed on the rooftop of buildings, even if Air Force One - the US President's official aircraft - ends up landing at Paya Lebar Airbase, sources told The Straits Times.
The same scene is believed to have played out when then US President Barack Obama was here in 2009, and when President George W. Bush visited in 2003, and again in 2006.
All three times, Air Force One landed at Paya Lebar Airbase, which is considered a more secure airport than Changi.
For security reasons, the use of decoy flights - sometimes two or more - is not unheard of when the US President travels, The Straits Times understands.
It is also a common misconception that Air Force One is the name of an actual aircraft, when in fact, it is a radio call sign for any US Air Force plane carrying the President.
In 2003, for example, when President George W. Bush visited Iraq, Air Force One is believed to have been a Gulfstream jet.
Planning for a presidential flight is a covert operation, with decisions such as where to land and which flight path to take sometimes made at the last moment.
"There is always plan A, B, C, so we have to be prepared for any scenario," said a source familiar with security protocols for such visits.
"When Mr Trump flies in, we will be ready for him to land at Changi or Paya Lebar and even Seletar airport for that matter.
"The decision will eventually be made by security agencies, including US Secret Service agents who will be on the ground here as well as in the control tower," said the source, who asked not to be named as he is not authorised to speak to the media.
In some situations, the landing site is finalised only about an hour, or even less, before the plane touches down.
It is believed that when President Obama flew to Singapore in 2009, the original plan was for him to land at Changi Airport. But this was changed about 45 minutes before landing, and the aircraft went to Paya Lebar instead.
Before Air Force One can get here, the plane, which does not have the range to fly from Washington to Singapore non-stop, will have to break its journey to refuel, although this can technically be done mid-air.
On flights to Asia, it typically stops at US military bases, for example in Alaska, Germany or Japan.
In an article, The President's Secret Air Force, which was carried in US-based Politico Magazine in May last year, writer Garrett M. Graff said that while the blue-and-white Boeing 747 is the most visible symbol of presidential travel, "there is much more that unfolds behind the scenes".
"A presidential trip involves hundreds of military and government personnel and often requires dozens of flights, including a backup for Air Force One and transport planes that move the motorcade, helicopters and communications gear," the article said.
The air fleet includes a few special presidential aircraft, known as C-20Cs. These are believed to be Gulfstream jets - similar to the one that carried President Bush to Iraq in 2003 - that can cover long distances.
"The planes don't really officially exist. But for years, they have gone nearly everywhere the President travels, paralleling presidential trips, serving as his chameleons, blending in anonymously at airports close by presidential visits - but never at the same airport where Air Force One itself is landing," the article added.
And then there are the cars.
When Mr Trump visited Asia in November last year, the US Secret Service tweeted out two photos of at least six vehicles - including the presidential limo nicknamed "The Beast" - being brought along inside a US Air Force C-5 Galaxy Transport.
The Beast and an identical decoy are often part of the President's overseas travel, and they come equipped with a whole range of security features. The cars are bulletproof and bombproof, airtight with an independent air supply in case of a chemical attack, and carry blood that matches the President's blood type.
Mr Michael Daniel, an international aviation consultant, said: "Preparing for presidential flights can take weeks, even months.
"For high-level engagements such as the upcoming summit in Singapore, security is top of the agenda for the US Secret Service, so you can expect that there are and will continue to be intense discussions and collaboration between the different US government agencies and the Singapore authorities," he said.
