A lot of people are asking me at the moment about how safe it is to fly when swine flu appears to be spreading. So, to get the authoritative word on the possibility of catching swine flu on planes, I asked the experts at Virgin America about air quality and here's their response:

'For Virgin America's Airbus A319, the volume of the cabin is 120 sq meters. The density of air (at sea level) is 1.2 kg/square meter. That means the total weight of air at sea level is 144 kg. Fresh air comes in at the rate of 0.849 kg/second. Therefore the air in the cabin is completely replaced every 2.8 minutes.

'Also, the new Airbus A320-family planes recirculate and resterilize 100 percent of the cabin air every 3 minutes. Fresh air is pumped into the aircraft from outside (where it is sterilized at -75 degrees, then heated to 800 degrees in the engines and cooled upon re-entry). The air vents flow vertically from overhead as well and then are vented downward, so that air is not circulated horizontally.

'All of this means that you are essentially in a safer environment than in a theatre, restaurant or other enclosed space. Additionally, all the Virgin America aircraft are equipped with HEPA filters rated at 99.97 percent efficiency for filtering out 0.3 micron particles. The filters are similar to those used in hospital applications.'