Enrico what a legend !!! Will try it once i have time tomorrow

 

So how come when i'm at cruise this was recently when i was doing tutorial 2, i lowered the speed on one of the legs and the aircraft slowed down for that speed i put in? Or does that fit into kriva theory?

Pcubine they engaged last night not sure why they didn't before!

 

Hi Vernon,

 

the leg or waypoint you are talking about is OEV18, (see pages 0.00.105 and on, tutorial #2) where the tutorial says we must use FLAPS 15 maneuvering speed, which implies we have to slow down the aircraft. Well, this is a different phase of flight,where we are descending, and we can enter lower speeds in the FMC, in this case the aircraft will slow down before reaching OEV 18, or at least try to, you might have to lower the gear as the tutorial suggests, or, if that is not enough, you might read " DRAG REQUIRED" on the FMC scratchpad.

In this case, the FMC, which in itself is a calculator, will recalculate a new T/D and speeds to meet the required speed restrictions.

The case we see with the SID, has the aircraft in a climb phase, and here, due to close proximity to EGLL, the procedure wants you to fly at or below 250 up to a certain point, and then slow down to max 210, before accelerating again. Here if you enter a lower speed, as is the case, the aircraft won't decelerate, you have to intervene, we are in a different phase of flight, that is how it works.

 

Legend is my name....lol...just kidding, I am just plain Enrico. :wink:

As the first speed restriction is 250 or BELOW, why not modify this speed restriction to 210 ? This way, there is no need to reduce speed for the next speed restrictions ?

Hey Rotor, 

 

This is a very interesting question, indeed. We should ask the UK CAA, (Civil Aviation Authority),why they set up the speed restrictions like that. Although I might kinda know why. 

 

Consider that, for every IFR procedure existing in a terminal area, whether a SID, STAR, IAP, they where designed and thoroughly tested by test pilots from the local Civil authority,in this case the CAA, to make sure they are safe and speed up traffic in and out of airports. My belief is that  by letting the aircraft fly up to 250 kts right after take off, they want to make sure the aircraft can get up and out of the airport traffic in a fast and orderly way. Once the aircraft has reached a safe altitude, and is stable, then they slow it down, but not to much, 210 kts. So, the way I see it, the purpose of a higher speed restriction before a slower one is to get the aircraft up and safe from terrain, and to get it out of the airport area. Bear in mind that the main purpose of ATC is to assure a safe and orderly traffic in the sky,

 

There is one more reason for this departure: noise abatement. At Gatwick you have to be at or above 1210 ft once you pass 6.5 km form the start of roll, in order to generate no more than 94 dBA from 07:00 to 23:00 LT over the area. In order to do that, the procedure wants you to fly a climb gradient of around 243 ft per nm to at least 3,000 ft, to ensure progressive noise reduction. Around Gatwick the Civil Authority has placed noise monitoring devices that monitor the noise level of aircraft. Well, as 250 kts is the general speed restriction below FL 100 , they let the crew fly up to that speed to meet those noise requirements. Once you are far from the airport, there is the issue of traffic from nearby airports, mainly Heathrow, and that is why they keep you low till BIG vor, at a lower speed, max 210 kts,the latter again due again to noise abatement.This time though you are already airborne, and do not have to climb above 6,000 ft till after BIG. So the aircraft does not need all the power to climb, and 210 kts is considered a general safe speed.

 

This pretty much sums it all up.

 

Enrico  

Legend!!! Thanks guys