speed below 10,000FT?

yes stay under 250knots.

groundspeed is in mph. not only are knots and mph different but at higher altitudes the air is thinner - less air enters the pitot tube and it reads a slower speed.

Anonymous wrote:

do they really keep under 250kn nuder 10,000ft in both climb and descent?
I was flying out of Houston the other day and the in-flight monitor said like 318MPH during climb, which even converted still more than 250kn.

I alwasy keep under 250 on the flightsim, but look like real pilots are speeding??!!?!

Yes, but they haven't always. Years ago, there were sporadic collisions, which had a trend of occuring below 10,000 feet where traffic density was greatest. At this point, aircraft were often doing over 300kts which made ATCs job of separating traffic hard - 250kts restriction speed being safer for all involved 😉

Does that speed vary for different aircraft and weights? I mean to say does the A380 and 747 also need to obey that? It would be difficult if the aircraft was heavy.

that's what flaps are for. an a380 or 747 gets off the runway at 150 - so 250 isn't an issue.

for jets such as the 737 the economical climb is around 230knots.

Mc_GaNgStA wrote:

Does that speed vary for different aircraft and weights? I mean to say does the A380 and 747 also need to obey that? It would be difficult if the aircraft was heavy.

Sometimes not. If they are heavily loaded, then V2+10 has the potential to exceed 250kts, for which the Captain will ask permission from ATC to exceed the restriction of 250kts, which will nearly always be approved. The fact that it is only a very small minority of aircraft in this position doesn't cause it to be a problem 😉

so is it 250kt True or Indicated airspeed? (not like I really know the difference anyways!)

Hinch hinted at the cause for the speed you saw on the monitor but there is more to consider.

The speed on the monitor is ground speed in statute miles per hour, usually derived from the GPS system. So, you have to convert first from knots to miles per hour. 250 knots converts to 287.7 (rounded) knots, Second, you have to consider the effect of wind on groundspeed. A headwind will result in lower ground speed and a tail wind will result in a higher ground speed at the identical airspeed. If the wind is directly on the tail, there is a mile for mile increase in ground speed.

For instance, in your example, if the a/c airspeed was exactly 250 knots, you could estimate the wind speed was the equivalent of 26.3 knots on the tail (subtract 287.7 mph of airspeed from actual groundspeed and convert the difference from mph to knots).

Anonymous wrote:

so is it 250kt True or Indicated airspeed? (not like I really know the difference anyways!)

Indicated airspeed. That's the only speed that's useful to know in an aircraft; it is a measure of the dynamic stress (air pressure on the aircraft due to moving through the air). Especially in jets, which can easily exceed a safe speed, because excessive dynamic stress can tear the wings off. And that usually results in someone having a bad day.

Until you're flying very high and fast, when mach number becomes more useful.

Ed

in the UK you can fly at Vref +100 under 10,000 without needing special clearance on departure.

so a transatlantic 747-400 would likely be climbing at 265KIAS without needing to request it specifically.
Once you get out of the SID/ATC traffic seperation vectors, ATC will normally clear you to your next waypoint and at the same time also clear you to speed up without you needing to ask specifically for it. (traffic permitting).

On the way back down 250knots is the norm unless cleared by ATC otherwise.