Pilots first heard about a Chinese live-fire naval exercise near Australia last week when already in the air, receiving messages that forced some to change paths through a busy air corridor, satellite text messages to and from pilots seen by Reuters show.

The incident highlights how airlines are increasingly having to react at short notice to geopolitical disruptions and military hazards, such as missile and drone barrages between Israel and Iran last year.

It also shows how China’s military, in its first drills in the Tasman Sea between Australia and New Zealand, is raising tensions by being more assertive across the Indo-Pacific region, including near Taiwan.

Planes first heard about a live-fire drill when a Virgin Australia pilot picked up a Chinese navy broadcast on the 121.5 MHz emergency radio channel pilots use to communicate between planes at 9.58 a.m. Sydney time last Friday (2258 GMT on Thursday), according to Australian officials.

The pilot reported the broadcast to an air traffic controller, who passed the message to Australia’s military, according to Airservices Australia.

“At that stage we didn’t know whether it was a potential hoax or real,” said Peter Curran, deputy CEO of the air traffic control agency, at a parliamentary hearing this week.

Air traffic control started sending hazard alerts to nearby aircraft, including a Singapore Airlines flight from Christchurch to Singapore and an Air New Zealand flight from Auckland to Melbourne around 11:30 a.m., according to previously unreported text messages.

Half an hour later, the Air New Zealand pilots told the ground: “Hi, lots of chatter on 121.5 including Chinese navy. Same pos[ition] and ht/radius as you advised. Cheers.”

An airline dispatcher told the Air New Zealand pilots 20 minutes later there was “unannounced live firing in Tasman to the nth of you by Chinese military.”

“Below is all we know. Broadcast on 121.5... just FYI we have been notified of a Chinese live firing exercise as follows. Posn. 37S 15702E. Radius 40nm. SFC-45000. Until 0300Z. No ack required.”

The messages were sent between aircraft and ground stations using an Aircraft Communications Addressing and Reporting System (ACARS) system.

LEGAL BUT ‘IRRESPONSIBLE’

Civil aircraft have been shot down by military assets highlighting the risk of live fire, including Malaysian Airlines flight MH17 over eastern Ukraine in 2014, a Ukrainian flight departing Tehran in 2020 and a suspected incident involving an Azerbaijani jet over Russia in December.

The Chinese warships were beyond Australia’s 200 nautical mile (370 km) exclusive economic zone on the high seas, where countries routinely do live-fire exercises, and China has said the warning it provided complied with international law, which Australia has acknowledged.

However, Australia and New Zealand have said the drills fell short of best practice for notifications.

“In that sense, it was irresponsible,” Australia’s defence force chief Admiral David Johnston told a parliamentary committee.

Pilots are typically alerted to military drills, rocket launches and other airspace issues through Notices to Airmen, or NOTAMs, which are usually filed at least 24 hours in advance.

“We/re don/t have a NOTAM in effect for Chinese exercise. Have not seen or heard any of that,” an airline dispatcher told two American Airlines flights approaching Sydney and Brisbane from the U.S. at 3:37 a.m. and 3:39 a.m. on Saturday morning.

Steve Cornell, a Qantas captain and a vice president of the Australian and International Pilots Association (AIPA), said the unexpected incident would have increased the workload on pilots and air traffic control.

“The issue with this one was the short notice, or no notice effectively, really,” Cornell told Reuters. “All of a sudden it came to the attention of the pilots and they had to self-manage maneuvering around this zone.”

Routings were changed for 49 flights last Friday, Airservices said.

Eight hours after Airservices first heard of the live-fire warning, air traffic sent a hazard alert to an Emirates flight from Christchurch to Sydney, but said they have “reports that the activity has finished”.

However a second live-fire warning came on Saturday afternoon, New Zealand’s defence ministry reported.

On Sunday, an airline dispatcher told a Virgin Australia flight about to depart Queenstown, New Zealand for Brisbane: “FYI the govt has confirmed Chinese navy now well south in southern ocean”.

The ships are now south of Australia and heading west, New Zealand’s military said on Friday.