Investigations are underway after two Cathay Pacific captains suffered loss of eyesight on two separate flights earlier this year.
In both incidents, first officers were forced to take control of the planes and land them under emergency conditions.
- Cathay Pacific confirms A350-1000 to be introduced on NZ routes
- How safe is air travel in 2019?
- More safety concerns over Boeing Dreamliners as whistleblowers complain to FAA
While no passengers suffered injuries and the planes weren't damaged, Hong Kong's Civil Aviation Department (CAD) has classified both episodes as "serious incidents" as part of their investigations.
The latest instance took place on Cathay Pacific flight CX170 between Perth and Hong Kong on February 21, 2019.
"The captain informed the first officer that he felt out of breath and his vision was impaired. The captain then declared he was incapacitated," the CAD report reads.
A passenger assisted in providing oxygen to the captain while the senior flight attendant helped the first officer in the cockpit of the plane.
The plane then descended to a lower altitude to reduce cabin pressure, helping the captain recover, before being granted priority access to Hong Kong International Airport where it landed without incident.
In January, flight CX583 between Sapporo and Hong Kong was disrupted after the captain suffered a sudden loss of vision.
After handing over control of the flight to his first officer he voluntarily strapped himself down in his chair "to prevent any possible interruption with the operation of the aircraft".
As with February's flight, the plane was granted priority approach to Hong Kong International Airport and landed safely.
On January 28, 2016, a British Royal Air Force pilot lost sight during a training flight in a jet in North Yorkshire. Another jet was scrambled with an instructor on board that helped the impaired pilot to land safely.
At the time, the Telegraph reported that his vision was affected by the sudden deterioration of an eye infection.