An aircraft carrying a woman who needed urgent medical attention was refused permission to land at Southampton Airport because it was closing.
The woman was being flown on an Aurigny medical evacuation flight from Guernsey because she needed treatment in the UK. The flight was diverted to Bournemouth.
The airport said the National Air Traffic Service (Nats) was unable to staff its request to stay open.
Nats said it was working "to try to ensure this does not happen again".
Aurigny said the patient had suffered head injuries and was being transferred with a nurse to Southampton General Hospital on 31 October.
The flight was due to land at Southampton Airport at 2310 GMT - behind schedule - due to delays while the patient was being stabilised, followed by a "technical delay".
"Permission to land after 2300 was refused by Southampton [Air Traffic Control]," the airline said, adding it then arranged to fly the woman to Bournemouth Airport, 30 miles (48km) away.
"The ambulance waiting at Southampton Airport was then driven to Bournemouth to collect the patient," an airline spokesperson added.
The woman was then taken to hospital in Southampton as originally planned, where she remains in intensive care.
In a statement, Southampton Airport said: "Some of these flights are outside of the airport's normal opening hours and are facilitated wherever possible.
"On this occasion Nats were unable to provide staffing cover beyond our closing time."
A spokeswoman for Bournemouth Airport said it was able to accept the flight because it took a "limited number" of aircraft outside normal operating hours and had both air traffic control and fire personnel on duty.
Nats said in a statement: "We're working with [Southampton] Airport to try to ensure this does not happen again."