Sixteen seconds. That is about how long the crowd at the National Day Parade gets to see the state flag in all its glory during the flypast each year.

But for the Republic of Singapore Air Force flight crew behind the feat, it is a different experience.

Yesterday, The Sunday Times went on board a Chinook helicopter to peek behind the scenes of the flypast segment at the first National Education show.

It was watched by more than 24,000 spectators, including primary school pupils from 59 schools.

The parade reviewing officer was Second Minister for Finance and Education Indranee Rajah.

STEP 1: ROLLING

Two days before the parade or rehearsal, the flag is rolled at Sembawang Air Base.

Measuring 30m by 20m, it is larger than a tennis court when unfurled and takes about 25 men to painstakingly roll, tuck and secure it.

STEP 2: RIGGING

The flag is then transported to Pulau Sudong for rigging onto a Chinook helicopter. Shackles, along with three ballasts each weighing about 226kg, are attached to it. The entire set-up weighs over 1,000kg.

STEP 3: RELEASE

It takes up to 1½ hours from the time of the flag pick-up to its release.

Along the flight route, the crew keeps a watchful eye for landmarks that can help gauge how much time they have to get to the correct position.

It needs "utmost cooperation between the crew and the pilots", said First Warrant Officer Vijaikumar Rangabashayam, an air crew specialist.

The helicopter makes its entrance overhead the Padang somewhere around the middle of the national anthem. 1WO Vijaikumar is prone on the floor of the helicopter, near an open hatch where he can get a good view of how the flag unfolds and the adjustments the pilot may have to make.

Even when the Chinook has flown past the Padang, people are still watching it along its route, and the integrity of the flag is maintained until it is out of sight.

STEP 4: RECOVERY

The Chinook circles back the way it came and drops the flag in Pulau Sudong, where the shackles and ballasts are removed and the flag is folded back up.

Said 1WO Vijaikumar: "You feel a sense of pride when you see your own state flag flowing majestically in the wind. It's an honour to be part of the team that does it."

Correction note: This article has been edited for accuracy.