When Singapore decided to build a new and bigger passenger terminal at Seletar Airport - which opened in November - the plan was to introduce an Instrument Landing System (ILS).

Such a system, installed at many other airports, uses ground instruments to help air traffic controllers guide pilots coming in for landing.

Without an ILS, pilots have to rely on just their vision, which means they cannot land in bad weather, for example.

Pilots typically prefer an ILS because it offers a more precise landing path, experts said.

Malaysia, however, protested and its carrier Firefly suspended all flights to Singapore from Dec 1, the day it was supposed to move its operations from Changi to Seletar Airport.

Malaysia claimed the new landing procedure would restrict developments at Pasir Gudang town which is near Seletar Airport.

Singapore has denied this, saying that the use of ILS at Seletar Airport does not change existing height limits.

The flight path and height limits are in accordance with safety and operational standards prescribed by the International Civil Aviation Organisation (ICAO), the Republic has said.

In objecting to the proposed ILS at Seletar Airport, Malaysia has also claimed that Pasir Gudang port will be subjected to higher risks.

Experts, though, have dismissed this, saying that for more than three decades, Singapore has safely managed the nexus between aircraft operations and ships transiting the Johor Strait to Pasir Gudang port.

Systems such as the Civil Aviation Authority of Singapore Vessel Height Measuring System are in place to safeguard both aviation and maritime activities.

Flights get held back while tall vessels cross the Strait of Johor.