Monday, July 18, 2011

Congestion in airports--landing at Logan

One of the things that makes airports congested is the safety margin needed between planes as they takeoff and land. So I was a little surprised when, walking along Boston harbor, I saw planes landing simultaneously on parallel runways at Logan airport. Here's a picture.


Apparently it's been going on for a long time, quite safely. Ben Edelman points me to the DRAFT MANUAL ON SIMULTANEOUS OPERATIONS ON PARALLEL OR NEAR-PARALLEL INSTRUMENT RUNWAYS (SOIR)

And Jerry Green gives the rules for Logan, with the aid of this airport diagram:


(http://204.108.4.16/d-tpp/1107/00058AD.PDF )

Jerry writes:
"There are a couple of combinations of runways that can be used simultaneously for landing.  Ideally Logan likes to have three active runways: one will be for landing only, one for departure only and the other one can do both, depending on the wind and the types of aircraft involved.
You will need to look at the attached airport diagram to make sense of what I will say below.
The only combination at Logan where both landing runways are instrument runways (i.e. conducting instrument approaches, possibly in bad weather) is where they land on 27 and 22L and depart on 22R. In this case the aircraft cleared to land on 22L is told to “hold short” of 27, and that means that they are not allowed past the point marked LASHO (Land and Hold Short Operations) on 22L. Usually the aircraft sent to 22L are turbo props, small private jets or smaller things (like Cape Air). They can easily make the LASHO restriction.  The larger jets get to use all of 27.
In the other combinations that allow two landing runways one of them is conducting visual approaches, and in most cases  that runway does not even have the equipment to conduct instrument approaches.  These are:
Land on 4R and4L. This is the picture you have sent (I can see that from the fact that they are both over the harbor) – 4R is an instrument runway but 4L is a visual runway.  In this configuration runway 9 is used for departures only (it is not an instrument runway and no one ever lands on it because their approach would come very close to hitting the State Street Bank building downtown).  This is the most common three runway configuration since Logan frequently has a sea breeze from the East in the summer, favorable for this set up.
Another one is landing on 27 and 32, and departing on 33L.  Here 27 is an instrument runway and 32 is a visual runway. Another factor in this set up is that the final approaches for 32 and 33L would cross each other about 5 miles out, so even though they are almost parallel they can’t both be landing runways at the same time.  But as 27 and 32 to do not intersect, they can be used for landing at the same time.  This is a common set up when there is a strong Northwest wind.
That’s about it for simultaneous landing operations with three runways in use.  There are quite a number of two runway configurations with intersecting runways which can be used when things are not as busy. One of these is landing on 15R and departing on 9, used frequently on bad weather days with strong winds from the Southeast. This is a particularly difficult one for the controllers as they don’t like to use the LAHSO restriction on 15R, holding short of 9, when the weather is bad.  Pilots add a little extra speed in gusty winds which makes the aircraft take a longer landing rollout.  They have to be sure they can make the LASHO restriction.  If a pilot is asked to do LAHSO and he has any doubt about it, then he is supposed to say that he is “unable” and the controller will delete the restriction and not let the other aircraft depart on runway 9 until the landing aircraft has stopped or exited onto a taxiway. That slows things down and reduces the airport’s capacity.
All this makes Logan an interesting case of “aircraft choreography”.  

2 comments:

Dan Craig said...

Thanks for posting the Jerry Green's explanation. A lot of aviation can appear mystifying to those not involved, and it's great to read a non-shrill piece about a newly-learned, seemingly frightening fact.

Your picture is great, and reminds me of this one. http://www.guy-sports.com/humor/pictures/picture_plane_illusion.htm

In this case, and it looks like a similar situation in your picture, the aircraft are in reality several miles apart, but because if their big difference in size, they have the illusion of appearing much closer than they actually are.

east midlands airport parking said...

Speaking as a tourist, this is really interesting stuff. We don't see the half of what goes on in airports really do we?