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No-wind conditions at parallel runway airports:

Posted: Thu Jan 13, 2022 1:48 am
by BN727227Ultra
On a mild, calm day at STL (late-1960s), I saw four consecutive aircraft take off in four directions (6, 24, 12R, 30L).

On a calm day present-day--ATL for the sake of discussion, can there be different flows on different runways, or still all-east or all-west like on a 'normal' day? Or does that mess things up too badly?

Re: No-wind conditions at parallel runway airports:

Posted: Thu Jan 13, 2022 3:02 am
by adipasqu
At LAX (4 parallel runways), their night ops will land aircraft to the east on the North complex while departures are to the west on the South complex for noise abatement reasons assuming weather/winds cooperate. During the day you would never do this as it will kill the arrival rate since you couldn't do simultaneous parallel approaches to both complexes. In general, to get the most efficient use of airspace and runways, you want all traffic going the same direction. This is a big reason O'Hare has reconfigured its airfield from essentially 3 sets of intersecting runways to a now mostly all parallel setup save for the two crosswind runways.

Re: No-wind conditions at parallel runway airports:

Posted: Thu Jan 13, 2022 3:35 am
by Starlionblue
Your example is from late 60s. Much less traffic compared to today (pre-Covid), so that stuff is possible. Nowadays, traffic volumes mean you'll typically just see unidirectional traffic at busier times.

In many places, e.g. HKG, HND, and BKK, a certain direction is preferred, typically due to noise abatement, so if winds are light that's what you get by default.

Re: No-wind conditions at parallel runway airports:

Posted: Fri Jan 14, 2022 2:39 pm
by BN727227Ultra
Thanks, both of you!

Re: No-wind conditions at parallel runway airports:

Posted: Fri Jan 14, 2022 11:33 pm
by N1120A
Noise and other environmental concerns pretty much run the preferred format of flow, as does airspace. LAX is a key example of both. The airport is right on the coast and basically at one end of an airspace that includes a bunch of other airports, so it makes sense to go the way they do.

Re: No-wind conditions at parallel runway airports:

Posted: Sun Jan 16, 2022 6:32 pm
by Cubsrule
N1120A wrote:
Noise and other environmental concerns pretty much run the preferred format of flow, as does airspace. LAX is a key example of both. The airport is right on the coast and basically at one end of an airspace that includes a bunch of other airports, so it makes sense to go the way they do.


In a few places, counter-flow operations happen for other operational reasons. SAN in low visibility is a good example. 27 departures are almost universal, but 9 has an ILS and 27 does not so when the marine layer sets in they land and depart over the ocean.

Re: No-wind conditions at parallel runway airports:

Posted: Tue Jan 18, 2022 5:05 pm
by futureatp
I've seen this happen at KPHX several times. Every now and then during night ops and then also right around the 12:00 hour.

Typical calm wind Phoenix ops are, departures arrivals heading to the East and then a switch over to the west. I never did ask as to the exact reason why.. Almost as if there is a slight prevailing wind away from the angle of the sun there. Switchover happened during a break in US Airways arrival departure banks (showing how long ago it has been since I've seen this). Every now and then I'd catch a departure and arrival opposite direction of each other. Two NW 757s come to mind as aircraft I've seen heading the opposite direction of each other.

Night time I would imagine just for convenience as nothing much is going on after the red-eyes departed.

Re: No-wind conditions at parallel runway airports:

Posted: Wed Jan 19, 2022 6:34 pm
by rjsampson
Cubsrule wrote:
In a few places, counter-flow operations happen for other operational reasons. SAN in low visibility is a good example. 27 departures are almost universal, but 9 has an ILS and 27 does not so when the marine layer sets in they land and depart over the ocean.


Which brings me to another question about SAN, during no-wind conditions. Let's say the traffic is light. 27 departures are still going to be standard, but for Eastbound flights, could a pilot request a RWY 9 departure, to save considerable fuel rather than, say flying the the fuel-consuming ZZOOO departure (for example)?

Expanding that question: Where traffic and weather permits, is it common for pilots to request departures other than the active departure runway to gain favorable fuel-savings? If not, why?

Re: No-wind conditions at parallel runway airports:

Posted: Wed Jan 19, 2022 6:53 pm
by GalaxyFlyer
KSAN has a pretty good-sized weight penalty for 09, but if TOGW and local ATC allows, yes you could use 09.

Re: No-wind conditions at parallel runway airports:

Posted: Wed Jan 19, 2022 7:17 pm
by mxaxai
rjsampson wrote:
Where traffic and weather permits, is it common for pilots to request departures other than the active departure runway to gain favorable fuel-savings? If not, why?

I wouldn't call it common but it does happen occasionally at smaller airports or during less busy times.