Ever since BA introduced the flat bed in January 2000, "flat is better" has become something of an axiom in long-haul air travel. If you are flying long-haul on business, reasoning goes, you want spend as much of the flight possible sleeping. And how humans sleep best? Lying flat, of course.
BA certainly think so. The airline employed an ex-Nasa flight expert in the development of its flat bed and concluded that a good night's sleep depended on reaching the rapid-eye movement (REM) stage of sleep. REM kicks in after between 60 and 90 minutes of undisturbed sleep. That, BA says, is only achieved when people can shift position.
Talk to neurophysiologists about sleep, however, and the picture becomes much more complex. Not everyone needs sleep flat; not everyone can especially those who suffer breathing problems. We all know people who can sleep perfectly happily in chairs and trains. Yes, most of us will sleep better on a flat surface, if you are more than 5ft 10in tall and always fall asleep on your back at home, may find an economy class seat more comfortable than BA's 6ft flat bed.
That's because, unless your point to the sky rather than curling over, the BA bed effectively prevents you from stretching out - the capsule at head and the top of the bed front act like headboards. That would not concern you greatly if you habitually sleep on your side. But anyone who sleeps on their front, cushioning their head on their arms, will find the constricted space at the head equally uncomfortable.
A position that suits one traveller may leave another insomniac. A flick through some of the reviews posted at flatseats.com (www.flatseats.com/Reviews/psngrentry.htm) reveals a healthy difference of opinion on just about every seat in the sky.
Virgin Atlantic was quick to seize upon the narrow dimensions of BA's bed when airline launched its upper class suite. Their new seat is designed to flip over to become bed with a separate mattress thus ensuring there are no joints where the extended seat meets the ottoman supporting lower third of the bed.
Most importantly, for taller and stouter passengers, the bed is up to 10in longer and wider at the shoulders than BA's. On both airlines, it is worth asking for a seat on the upper deck. Virgin's beds are longer there and BA tends to assign noisy families seats downstairs.
Japan Airlines recently weighed in with a new twist: their new business class seat is flat but not horizontal, extending to an angle of 170 degrees. The airline JAL claims the difference goes unnoticed during a flight because aeroplanes fly at a slight angle and all its seats face forward.
The "shell flat seat", as JAL calls it, also has a built-in massage function for the lower back - and it is certainly detectable on land, although whether it can really be felt amid the general vibration of an airline cabin, it's hard to say.
The thought of a totally flat bed may be reassuring, but not everyone is convinced of the need for it. "When it's a question of 20 degrees, I would be surprised if you could tell the difference," says Dr Oliver Bernath, a neurologist who used to run a sleep clinic in Los Angeles before joining McKinsey as a consultant. What really helps travellers to achieve good quality sleep, he says, is light - or the lack of it.
"Light will interfere more with the body clock. It's important to get the right light." The sooner the cabin lights are dimmed and the later they go up before landing in the morning, the better you are likely to sleep.
BA confirmed that the recent introduction of "sleeper" services from New York and Dubai appeared to have gone down well with business class travellers. Passengers dine in the BA lounge before departure, and cabin lights are dimmed immediately after take-off, with no full meal service on board. "It was very well received," says a spokeswoman. "We do a nightcap service [on the plane]. And then we serve breakfast as late as possible."
Finally, of course, there is the effect of noise. Earplugs are an obvious recourse. If you sleep on your back or front, you could also try noise-cancelling headphones: Maplin ( www.maplin.co.uk) are currently selling a very reasonable fold-away pair for just under £20. Be warned: "People are more likely to snore if they sleep flat," notes Dr Bernath, ominously.
