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Originally Posted by MetroMPG
But is it strictly necessary to take off & land into the wind?
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Yes. Even just a 10-knot tailwind will significantly increase your takeoff and landing distances, potentially to the extent that you will not have enough room to abort or go-around if necessary. There are some very specific regulations that define how much room you must have (based on the manufacturer's official aircraft performance specifications for a particular loading and configuration). Safety is a major priority, because things do break and you always need a way out. Having the engine crap out on your car as you barrell down an onramp is inconvenient but is not likely to kill you. Having an engine crap out just before rotation speed on a runway that is not long enough (given the conditions) to abort the takeoff very well may kill you and your passengers.
Quote:
Originally Posted by MetroMPG
Is there a threshold wind speed below which it's not necessary?
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Yes and no. I can take off from my local airport (KGGG) in a light plane that might normally only require a 1500' distance to take off with a 20-kt tailwind because I have over 2 miles of runway in front of me. I'll have plenty of space to take off and it's not overstressing the plane at all. But the risks are higher. I'll be going a lot faster on the ground before having enough speed to take off (even though my indicated airspeed at rotation will be the same), and the consequences of a mistake are proportionately greater. The same applies for landing: the groundspeed will be significantly higher (requiring a lot more braking) and the distance required will be much longer (i.e. compare stopping distances in your car at 60mph and 80mph: the distance required at 80mph will be greater than the proportional increase in speed might lead you to believe).
Is it possible to land and take off with a tailwind? Sure, if you have enough room. Is it safe? Well ... Aircraft operators and pilots need to establish a habit and attitude of safety. Even with all of the automation and computer asisstance with which modern aircraft are equipped, a moment of inattention from the pilot can spell disaster.
With respect to aviation, safety needs to come before economy, always. I have a feeling that, in the long run, it's more economical that way.