SINGAPORE - A man who flew a drone without a permit in an open field in Punggol was aware the area was a "no-fly zone" but admitted it had "slipped his mind" when confronted by an officer from the Republic of Singapore Air Force (RSAF).

Tay Miow Seng, 41, also unlawfully flew the device at a maximum altitude of 431m - nearly seven times higher than the 64m limit in the area.

He pleaded guilty in court on Friday (Dec 27) to flying the drone for recreational purposes at the field within 5km of Paya Lebar Air Base without a valid Class 2 activity permit.

He also admitted to operating the device in a manner likely to endanger the safety of aircraft.

Deputy Public Prosecutor Dwayne Lum said if Tay had applied for the permit, the Civil Aviation Authority of Singapore would have required him to operate the drone under safe operating conditions to ensure the safety of persons, aircraft and property.

He added that these include obtaining clearance from the RSAF before operating the drone, to ensure its flights do not interfere with its operations.

The court heard that Tay and his friend Ed Chen Junyuan, 37, had each been flying a drone in the open field near Block 128C Punggol Field Walk around 9pm on June 26 this year. Both are Singaporeans.

The off-duty RSAF officer received an alert, informing him that a drone had been seen in the area by the Paya Lebar Air Base Aeroscope system.

Said the DPP: "The alert was broadcasted to all principal staff of the air base. It also stated the police had been alerted by the air base command centre and were being dispatched to the vicinity of the drone sighting."

The RSAF officer boarded his car, drove towards the open field and told the duo it was a "no-fly zone"

Tay admitted to him it had "slipped his mind" as he was excited to teach Chen how to operate his drone.

Police officers arrived at the scene about 10 minutes later and detained the two men.

Chen, who pleaded guilty in October, had become the first person to be convicted of the offence of flying a drone without permit. He was fined $2,000 last month.

Tay, represented by lawyers Josephus Tan and Cory Wong, will be sentenced on Jan 20 next year.

First-time offenders caught flying a drone without a valid permit can be fined up to $20,000. Repeat offenders can be jailed up to 15 months and fined a maximum of $40,000.