USA vs Canada ATC question

[heeypilot]

i was in the USA on a commercial flight.. we were holding short of the runway with a few to go in front of us and literally as soon as one jet was cleared for take off and rotated at the end of the runway, the plane on the runway behind it would start to roll right away. the aircraft ranged from 737's, to 757's, etc. most of the time there would be an immediate right or left turn after take off. looked pretty cool from the ground. do they not have wake turbulance seperation requirements in the US? just curious

[gumbofats]

I think there are 2 requirements for separation.

Don't know the procedures at said airport but for wake turb...I think it's

4456

4 is heavy behind heavy
4 is light behind medium
5 is medium behind heavy
6 is light behind heavy

light being 12500 lbs and less
medium being 12500 - 300 000 lbs
heavy being 300 000 + and at least here and I'm guessing ICAO standard including the 757 because of it's nasty wake characteristics and STOL ability.

So, strictly speaking about wake turbulence separation....

Medium behind medium has no wake turblence restrictions.
Heavy behind medium has no wake turbulence restrictions.

So for your example there are many combinations that could follow quickly behind each other. A 757 could easily follow a 737. A 737 could follow a 737. Depends on their order....

Also wake turbulence is always at the discretion of the pilot. It can be waived or increased, based on preference, experience, knowledge, or lack of knowledge of the pilots who are taking the risk.

I am pretty sure if a controller ever omits the protection mileage then a pilot should do whatever is prudent.....and I've never heard of a situation where there was ever a debate towards the more conservative end of this concept. In fact, many times pilots will request additional seperation and controllers are keen to give it even in the face of potential messes. No matter who forgot the rule of thumb from the books, we all say "OK LET'S JUST DO THE SAFEST THING".

As for the other (lateral) seperation aspect. I can only speculate that if it was tight.....they might have had different departure procedures. In which case headings (which are common at single SID departure sights) wouldn't be required. Or a visual was possible.

Hope that helps, it's just my understanding.

As an aside the coolest instructions I ever heard from a tower controller went something like this. Aircraft "A" "put the hammer down"...break....Aircraft "B" keep "A" in sight and follow him out!

Same aircraft type and both mediums.

Fly well,

Gumbo

[justplanecrazy]

Gumbo, you got the seperation standards right for Canada. In the states I believe the weight classes are heavier than here.

As far as keeping lateral seperation, that's where the turns come into play. You normally need 3 miles lateral regardless of weight. If you get a turn immediately after departure, then you can use a mile. If its a slower behind a faster, the front guy doesn't even have to be in the turn before you launch him as long as you keep your mile. By the time the guy ahead is rolling if you clear the second guy for take off, you'll end up with a mile so it'll seem like there's no seperation at all but they are running some.

The only problem is if you have a heavier aircraft in front, then you have to apply the wake turbulence seperation regardless of turns. Some pilots will request to waive the wake turbulence and some controllers will accept, some won't. I don't because I feel that IFR wake turbulence seperation will be determined the responsibility of the controller not the pilot if it ended up in a court room, because unlike VFR they can't manouver to avoid it, they're on fixed headings etc. If you're waiving 3 min's from an intersection or 2 min's behind a heavy, I'll blast you off with the regular wake turbulence sep standard, 4,5, or 6 miles, but I'll never waive the mile distances. Some controllers have a different interpretation of wake turbulence waivers and will only provide lateral seperation of 1-3 miles and no wake seperation at all.

I hope that clears it up.

[justplanecrazy]

Oh and in Canada everything from a 737 - 757 is a medium so no wake turbulence would be applied except for the 757 is considered a heavy if he's in front as they produce some pretty sick wake turbulence. In the US they probably consider it a medium regardless cause I believe their Heavy weights are the ICAO standard and heavier than Canada's. Canada is in the process of adopting the ICAO weights, so you can expect to see some changes if you really look for it.