SID Speed limits of less than 250Kt?

[cossack]

<a href="http://www.pprune.org/ubb/NonCGI/ultimatebb.php?ubb=get_topic;f=57;t=003556" target="_blank">Here</a> is an idea posted by me in Questions that seems to have gone a bit quiet. . .. .Could slower speeds on SIDs be used as a tool to increase departure rates?. .. .Anyone in here have any thoughts on the subject?. .. .Thanks

[Pegasus77]

As departures on most major airports are based on radar separation, I think it wouldn't make any sense flying slower, only takes up more time to get the required separation.... In case of timebased separation, A/C would become stacked even closer together.. . . . <small>[ 09 March 2002, 17:00: Message edited by: Pegasus77 ]</small>

[HEATHROW DIRECTOR]

Faster the better from a separation point of view... Contrary to previous answer, many major UK airports (Heathrow, Gatwick, etc) have departure intervals based on time, which frequently produces considerably less than "radar separation".

[cossack]

I think where this idea came from is an effort to increase the number of departures possible from a runway that is relative restricted on SID routes due to noise. . .. .E.g. All SIDs except one are considered "same route" for departure separation purposes and this one route is type limited to turbo-props and light jets. Therefore all same type departures on these other routes are 2 minutes apart except for an on-going trial where two other routes are 1 minute splits (not wheels up but 60 seconds between rotations!) What you have is a slow aircraft on departure that requires a 4-minute interval prior to the next fast departure. No turns off the SID are permissible due noise and you have nothing to fill the gap. Pretty restrictive on a departure only runway isn't it? . .. .If all aircraft were restricterd to a maximum of 210Kt you could reduce the departure interval between slower and faster and when radar separation was established lift the speed restriction. Many jet aircraft don't accelerate to 250Kt until above 3000 feet anyway, so the difference would hardly be noticeable in aircraft performance terms but could perhaps yield a useful benefit in departure flow rates.. .. .The present time based departure separations are excessively restrictive because the following aircraft can accelerate (but perhaps won't immediately) to 250Kt and will erode the distance to the previous departure, hence the 4-minute interval.. .. .Other ideas.... .. .What about departure separations based on distance? They aren't used in the UK to my knowledge but are elsewhere. The 2 minute rule has been around for a long time, since when aircraft performance has improved greatly. You wait 2 minutes now and you get 8 miles and 5000 feet! . .. .The receiving controllers (Area) who work on a radar range that is less than ideal for close-in work due to sectorisation and are required to use 5 mile separation due to an off-site source being used. Perhaps use of a Departure Radar Controller (catcher) responsible for initial separation and routing would be better?. .. .There is more than one solution to this problem but most of them are quite radical and political. . .. .Sorry if I've gone on a bit. I guess its all this spare time we have between departures to think of better ways of getting the job done!. .. .Time for a lie down.... . . . <small>[ 11 March 2002, 09:50: Message edited by: cossack ]</small>

[Sniff]

Cossack - One thing to mention is that on take off, many aircraft will not be clean if asked to fly 210Kt. Even my 737 when departing over 53T is unable to do this, and the DC10 is another matter still I believe.. .. .On a 737 - At our accel alt (we use 1500' but some fleets will use 1000') the speed cursor will drive to 250kt, and the aircraft accelerated through flap retraction. It is not uncommon to be 250kt by 3000'.. .. .Most SID speed restrictions that I have found are mostly to do with a tight turn after departure, requiring a smaller radius of turn. Examples that spring to mind are DUS and ARN.

[Euroc5175]

The introduction of RNAV SIDs, using the existing P-RNAV design criteria, could result in speeds of less than 250knots being required to enable some of the initial large turns required by existing Noise Preferential Routes to be flyable.

[HalesAndPace]

Sniff, how do you adjust the "automatics" for the SIDs (quite a few of them, for noise abatement purposes) that state maintain V2 + 10 knots until 3000 feet agl, or, those with steep gradient requirements?

[1261]

The departure radar controller (using airport radars and hence needing only 3Nm separation) has been talked about for the Scottish TMA; in my opinion it's by far the most efficient way of getting large numbers of aircraft out of the terminal area as quickly as possible - especially if you've two (or more) airports in close proximity.. .. .But it'll never happen, because it'll need extra bodies.....

[Sniff]

If you need a V2+15 climb, then you don't engage the automatics! Seriously though, to get into the accel mode, we would press VNAV. This reduces to climb power, and starts the acceleration. If you just want to climb, then at 1500' pressing N1 on the mode control panel engages climb thrust, and the flight director/autopilot will maintain V2+15 (about) until 3000' when you engage VNAV to start accel. Most of these procedures were designed (I think) for Chapter II aircraft, which will be gone soon!