Was wondering if someone could explain to me how it is determined whether or not to use the full length of a runway vs. an intersection for departures. Two examples that raised this question for me: 1) flew out of ORD last Saturday and we were instructed to taxi to 28R and depart via the N5 intersection but as were in line, ATC pulled us out and told us to taxi all the way to the end for a full length departure. I was listening on the LiveATC app and our pilots seemed somewhat confused and asked why and ATC basically said they just wanted us to go down there. 2) at OKC a few weeks ago, we had to hold for flow into DFW and as we were sitting at the end intersection to 17R a WN flight taxied up and took the intersection which was only a few feet ahead and then back taxied to the end did a 180 and departed. I was scratching my head because it was only a few feet and just seemed like a waste of time. Do certain airlines mandate their pilots use the full length even if given an intersection? Appreciate any insight!

1) Oftentimes a heavy aircraft will require a full-length departure. I don't know the specifics, but I believe the next aircraft to depart after a heavy (i.e. you) requires extra time/distance for wake turbulence if it were to depart from an intersection. ATC can actually get departures out faster by sending out a few aircraft behind the heavy from the full length.

2) Most airlines get their takeoff performance data over ACARS. If the SWA crew didn't already have data for an intersection departure, it was probably faster to back taxi and depart full length instead of waiting for new takeoff data to load.

OKCDCA wrote:

Do certain airlines mandate their pilots use the full length even if given an intersection? Appreciate any insight!

The simple answer is yes.

Still the Captains discretion even if company allows LAHSO operations.

Okie

N353SK wrote:

1) Oftentimes a heavy aircraft will require a full-length departure. I don't know the specifics, but I believe the next aircraft to depart after a heavy (i.e. you) requires extra time/distance for wake turbulence if it were to depart from an intersection. ATC can actually get departures out faster by sending out a few aircraft behind the heavy from the full length.

2) Most airlines get their takeoff performance data over ACARS. If the SWA crew didn't already have data for an intersection departure, it was probably faster to back taxi and depart full length instead of waiting for new takeoff data to load.

Thanks for the response! Your first point makes sense, when we (AA 738) were instructed to go to the end, there was a UA 772 taxing down to the end and 3 RJ's behind us. By the time we got down to the end, I could see the 3 RJ's had already taken off as a B6 320 was now #1 at N5 so the UA 772 took off then we were right behind it and got up before getting any wake turbulence so then by the time we were up I'm guessing the B6 320 would have no issues from the UA 772. And kudos to the ORD controllers who clearly know how to do their job and keep things moving!

As for your second point, I guess I get it but I fail to see how departing one intersection up (~500 ft) makes that big of a difference on a 9800 ft runway unless it's just a matter of "doing it right" which I'm completely fine with.

N353SK wrote:

2) Most airlines get their takeoff performance data over ACARS. If the SWA crew didn't already have data for an intersection departure, it was probably faster to back taxi and depart full length instead of waiting for new takeoff data to load.

"performance data over ACARS"...... care define most?

If you have TO data for an intersection departure, you can always depart from full length or an intersection behind the intersection you have the data for but you are unable to do the opposite. If the SWA flight officially had full length numbers, to be legal for takeoff they had to position the aircraft as close to full length as possible. Seems silly until you or your company is forced to explain why they took off from a shorter position on the runway. On some runways feet can and have mattered. So for continuity of thought, you have to treat a 10k’ runway the same as a 6k’ one (to keep it simple).


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N353SK wrote:

1) Oftentimes a heavy aircraft will require a full-length departure. I don't know the specifics, but I believe the next aircraft to depart after a heavy (i.e. you) requires extra time/distance for wake turbulence if it were to depart from an intersection. ATC can actually get departures out faster by sending out a few aircraft behind the heavy from the full length.

2) Most airlines get their takeoff performance data over ACARS. If the SWA crew didn't already have data for an intersection departure, it was probably faster to back taxi and depart full length instead of waiting for new takeoff data to load.

There's still a wait even from the end. Our performance data came from the FMS not ACARS and if the intersection was in the database then you're good to go; if not no way. I remember several times having to depart against the departure flow due to some little piece of data in the FMS saying it wasn't legal.

I'm thinking this is obvious so pardon me if everyone knows this; It's quicker to have jets departing from 2 intersections and the end than one long line for the end. Also it might be a little more complicated than it seems. I've seen ATC let guys go ahead of me only because there were already a saturation going my way and they let guys go that were turning outbound in another direction.

CosmicCruiser wrote:

I'm thinking this is obvious so pardon me if everyone knows this; It's quicker to have jets departing from 2 intersections and the end than one long line for the end. Also it might be a little more complicated than it seems. I've seen ATC let guys go ahead of me only because there were already a saturation going my way and they let guys go that were turning outbound in another direction.

In the case of 28R/N5 at ORD, if memory serves, full length 28R would either cross or produce jet blast on an intersecting runway. So, for smaller aircraft, the intersection will work most of the time. If my memory is correct, the heavies or anyone else requiring full length may need separation on the intersecting runway for its departures or arrivals which can be done with advance planning.

N353SK wrote:

1) Oftentimes a heavy aircraft will require a full-length departure. I don't know the specifics, but I believe the next aircraft to depart after a heavy (i.e. you) requires extra time/distance for wake turbulence if it were to depart from an intersection. ATC can actually get departures out faster by sending out a few aircraft behind the heavy from the full length.

This is exactly why ORD does this. Standard separation from a departing heavy is 2 minutes however from an intersection that is raised to 3 minutes. Apparently the controllers feel that the extra minute is important enough to have a few aircraft depart from the full length.

mmo wrote:

"performance data over ACARS"...... care define most?

The industry may have moved on since you retired, it is a very common way to obtain validated performance data as various cross checks onboard (FM inputs vs ACARS) and remotely (eg comparing the load control TOW to the ACARS TOW) to reduce errors.

zeke wrote:

mmo wrote:

"performance data over ACARS"...... care define most?

The industry may have moved on since you retired, it is a very common way to obtain validated performance data as various cross checks onboard (FM inputs vs ACARS) and remotely (eg comparing the load control TOW to the ACARS TOW) to reduce errors.

Yeah, I guess the industry has moved on. I was only used to the old technology....Class III EFB....such stoneage technology. Again, still waiting for "Most". I think not. You might want to get out a little bit more and fly other than in the US.

Most aircraft do not have class 3 EFBs, I think Boeing’s class 3 solution only was certified under 4 years ago, as a customer option only available on some types.