Q:

Why have some governments banned outbound international flights in response to COVID-19?

Why have some governments banned outbound international flights in response to COVID-19?
For example, the Philippines initially announced (but later reversed) a ban on outbound flights:

Airports in Luzon [large island in Philippines where the capital, Manila, is located] will stop all outbound international flights starting Friday after the government gave a 72-hour window to all those who wish to leave the country after heightened measures were put in place to control the spread of COVID-19.
https://www.cnnphilippines.com/news/2020/3/17/Philippines-international-flights-coronavirus-Luzon-quarantine.html

The New York Times has an article on travel bans that identifies a few other cases of countries with outbound travel bans, including:

Namibia: "suspending inbound and outbound flights from Qatar, Ethiopia and Germany for 30 days"
Bolivia: "cessation of all flights to and from Europe"
Peru: "The measure means all international flights will be canceled. "

I understand the ban of inbound international flights to prevent contaminated individuals from entering the country, but banning outbound flights seems less obvious to me.

A:

Another possibility, ignoring fears of infection, is that the country doesn't want their citizens to become stranded in another country if flights are suspended at a later date. For example, on Monday, March 30th, the UK Foreign Secretary Dominic Raab announced a £75m plan to charter flights to repatriate stranded Britons, and also advised any citizens still in countries where commercial flights remain available to fly home as soon as possible.
If a country's citizens become stranded abroad it will usually end up being the government's responsibility to fly them home.

A:

There are a number of reasons that a country would want to restrict outbound flights.
Firstly, there is the issue of getting to the airport to catch the flight.  Someone catching a flight will interact with a transport provider (taxi driver, car rental company, etc), check-in staff, security staff, passport control, gate staff, and others.  These additional contacts increases the risk of transmission if someone has the disease.
There is also concern about what is coming in from overseas.  If the flight is being operated by a foreign airline, a plane and crew would have to come in from overseas to operate it.  If the flight is being operated by a national airline, the plane and crew that goes out will have to come back.  Either way, the crew will interact with enough ground staff to risk transmission if they get infected overseas.

A:

I expect there are three rationales behind this:

In the face of pandemics, there is a definite "run for the hills" panic mentality that can set in, sending hordes of people to airports. But airports — like any form of mass transit — are not the most sanitary places in the world, and are not designed for social distancing. An outbound airport crush would be a perfect place to transmit covid-19 to others.
Airports aren't only for arrivals and departures; many flights at major airports are layovers where planes refuel or passengers transfer to connecting flights. Someone waiting for an outbound flight in an airport might be casually exposed to any number of people passing through from one nation to another, without any way of knowing where those people had been traveling.
People who are likely to flee their homeland because of a fear of disease are equally likely to flee back to their homeland if they become afraid in the country they travel to, and nations have an obligation to repatriate their own citizens. That opens the opportunity for someone to unwittingly flee into a hot zone and then demand return, potentially as vectors for the disease.

Airports are just not good places to be during pandemics, for anyone, and restrictions on outbound flights as well as inbound will minimize the dangers those locales pose.

