By The Straits Times | Created at 2026-09-07 11:36:24 | Updated at 2026-09-07 12:34:09
1 hour ago
JAKARTA – Flight disruptions between Singapore and Jakarta could continue even after airports reopen if further eruptions occur or airlines decide it is not yet safe to fly, aviation experts warned.
Additionally, whether flights can operate will depend not simply on whether Anak Krakatau, a volcanic island located in the Sunda Strait, continues erupting, but on how much ash it produces, how high the ash rises and, crucially, where winds carry it.
“An airport can be closed, then reassessed, reopened, monitored, and if conditions deteriorate, restrictions can be imposed again,” Polana Pramesti, an aviation analyst from the Indonesian Aviation Association, told The Straits Times.
Even after an airport reopens, schedules may take time to return to normal.
“Reopening an airport is not as easy as just restoring a schedule,” said Susanna Jenkins, associate professor at Nanyang Technological University’s Asian School of the Environment.
“Aircraft and crew end up in the wrong places, crew duty-hour limits kick in, and there is a backlog of displaced passengers competing for seats on flights that were already busy,” she added.
Singapore was the international route hardest hit by the initial closure, ahead of Hong Kong, Sydney, Seoul, Doha, Amsterdam and Kuala Lumpur, according to Indonesia’s aviation authorities. All 33 flights scheduled to depart Singapore for Jakarta on Sept 6 were cancelled.
Seven Indonesian airports, including Jakarta’s main Soekarno-Hatta International Airport and Halim Perdanakusuma Airport, were due to remain closed until 11.59pm local time on Sept 7 (12.59 am, Sept 8 in Singapore). An eighth airport, Atung Bungsu in South Sumatra, resumed normal operations at 9am.
The disruption to flights has snowballed since Sept 6. Transport Minister Dudy Purwagandhi said about 2,300 flights and 263,000 passengers had been affected as at 9am on Sept 7, up from about 1,700 flights and 170,000 passengers the previous day.
Jenkins said Singapore-Jakarta is a very busy international route, so a prolonged closure at Soekarno-Hatta would cancel many flights at once and disrupt other services across airline networks.
Why flights could stop and start
Polana said the size of an eruption alone does not determine whether flying is safe; what matters more is whether ash reaches the airspace or airports.
Three factors have to be considered together: the amount or concentration of ash, the height of the ash column and the direction and speed of the wind.
“Volume or concentration describes how great the hazard is. Altitude determines which flight levels are threatened. Wind describes where and how quickly the hazard moves,” Polana said.
Volcanic ash can melt inside the intense heat of a jet engine and stick to critical components, potentially causing engines to lose power, while its abrasive particles can damage the fuselage and scour windscreens.
Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) said ash was detected as high as 50,000 feet (15.2km) to the west of Anak Krakatau on Sept 6, while ash spreading eastwards reached 20,000 feet.
Alvin Lie, chairman of the Indonesian Air Transport Service Users Association, said ash at higher altitudes can threaten aircraft already in flight, rather than only those taking off or landing.
“If the column is high, above 20,000 feet, it will affect aircraft at cruising altitude,” Alvin told The Straits Times. “If the height of the column is low, below 20,000 feet, what is affected are aircraft taking off and landing only.”
Commercial aircraft cruising between 30,000 and 40,000 feet could therefore be exposed when ash reaches those levels, he said.
Where the ash travels depends on the wind, Alvin said, adding that wind speed determines how quickly it reaches a particular area.
The changing wind conditions were evident on Sept 6. Transport Minister Dudy Purwagandhi said that by late afternoon, winds at 15,000 feet had shifted from westwards to eastwards, prompting the authorities to extend the closure of eight airports.
Polana said volcanic ash advisories typically forecast its movement about six, 12 and 18 hours ahead, but become less certain if the eruption or winds change.
Jenkins said eruptions can be episodic, with repeated explosions producing ash clouds over days, weeks or even longer, adding: “The time frame for how long these recurring eruptions that produce ash continue for is very varied and not easy to forecast before or during an eruption.“
Why reopening is not enough
Even after ash stops falling, an airport cannot necessarily reopen immediately. Alvin said ash must first be cleared from runways, taxiways, aprons and surrounding areas so aircraft engines do not blow it back into the air. Aircraft covered in ash may also have to be cleaned.
“Everything has to be cleaned, and only then can the airport reopen,” he said.
Even when an airport is declared safe, individual airlines still decide whether to resume flights, delay them, reroute aircraft or cancel services based on their own safety checks.
The consequences can spread beyond Jakarta. Alvin said about two-thirds of Indonesia’s domestic flights are linked to the capital through Soekarno-Hatta or Halim, creating a domino effect across the country’s aviation network when both are shut.
Indonesia saw a smaller example just days earlier, when Kualanamu International Airport, which serves Medan, temporarily closed on Sept 1 after ash from Mount Sinabung was detected at the airport.
Improvements since Eyjafjallajokull eruption
Aviation is far better equipped to deal with volcanic ash than it was a few decades ago.
Jenkins pointed to the 1991 eruption of Mount Pinatubo in the Philippines, when ash travelled across the South China Sea. At the time, she noted, there was no coordinated global system for warning aircraft about volcanic ash.
Today, volcanic ash advisory centres in Darwin and Tokyo cover the region, while satellite detection and dispersion modelling help airlines track ash and forecast where it will travel.
The 2010 eruption of Iceland’s Eyjafjallajokull, which led to more than 100,000 flight cancellations across Europe, “was a turning point”, Jenkins said. The episode improved understanding of how different concentrations of ash affect aircraft engines and led to a more graduated approach to closing airspace.
“The result is that today’s closures tend to be shorter and more geographically targeted,” she added.
For Singapore travellers, reopening Soekarno-Hatta would not mean flights immediately return to normal.
“When an airport is opened, it means that operationally the airport can be used, but it does not necessarily mean that all flights will immediately return to normal,” Polana said. “Recovery of the flight network can take several hours or even longer.”
