A reusable fabric mask is recommended, but "simple disposable masks or scarves" will also work, Lufthansa says
Three of Europe's biggest airlines are making the wearing of face masks mandatory for all passengers.
German carrier Lufthansa began asking customers to wear "a mouth-nose cover" on board from Monday, May 4.
"Despite numerous adjustments to service procedures, it is not always possible to maintain the required distance on a flight," it said. "Therefore, this measure serves as additional protection for all passengers."
A reusable fabric mask is recommended, but other types of coverings "such as simple disposable masks or scarves" can also be used.
Mask should be worn in the airport too, Lufthansa said.
Air France and KLM say they will ask customers to wear a mask "throughout their journey" from May 11.
The request is in line with French instructions making the wearing of a mask compulsory on public transport, Air France said, and customers will be notified by email, sms or via its website.
The announcements come as airlines around the world are examining ways to adapt health and hygiene protocols in a time of pandemic.
Last week, Ryanair's Chief Marketing Officer, Kenny Jacobs, told the Irish Independent that face masks are "definitely" part of its plans.
"Masks will be required either at all times, or at times when the [Covid-19] numbers are going in the wrong direction," he said.
In the US, carriers like Delta, American Airlines and United are also requiring passengers and crew to wear masks.
Airlines are currently carrying a fraction of the passenger numbers they normally would, and it remains to be seen what airport health measures - such as temperature screening or Covid-19 tests - will be put in place.
99pc of Ryanair's fleet is grounded, for example, while KLM has targeted a 15pc resumption of flights this month, with daily services including Barcelona, Madrid, Rome, Prague and Milan.
With low load factors, many have been spacing out passengers to achieve physical distancing on board, but there is debate as to whether leaving seats empty can be effective, or economic, in the future.
Lufthansa's policy of keeping neighbouring seats free in Economy and Premium Economy Class "will no longer apply, as wearing the mouth-nose cover provides adequate health protection", it says.
"Due to the current low occupancy rate, seats will nevertheless be allocated as widely as possible throughout the cabin."
Meanwhile, Aer Lingus said it will be reviewing processes and procedures after images of a crowded flight with no social distancing appeared on social media.
"In light of the unexpectedly high loads on the Belfast-London Heathrow service this morning and the level of demand for the route, Aer Lingus is reviewing its processes and procedures applicable to the operation of this service," it said.
"The safety and security of Aer Lingus' customers and crew is our top priority and any process changes that are identified as being required will be implemented as a matter of urgency".
Airlines have also been implementing enhanced cleaning systems, having crew wear masks and PPE (Personal Protective Equipment), and introducing ground changes such as Plexiglass protection screens and physical distancing in boarding queues.
"In principle, infection on board remains very unlikely," Lufthansa said.
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