Even though the airports are separated by only 20 miles or so, there is a big difference in the operations of both airports.
you have the huge hubs of both UA
, plus a lot of other airline traffic as well. Demand is obviously very high in this airport, at times approaching 90 aircraft per hour. On a good day weatherwise, ORD
will run either Plan X (East config) or Plan Wierd (West config). I believe X allows an Airport Acceptance rate (the number of planes per hour that an airport can land) of 100, and Wierd about 92. (Wierd is slightly less due to the fact that it relies on LAHSO on 22R). However, several things can affect this, and when you lose three landing runways at ORD
, your Arrival rate takes a hit, then also add into that increased separation for IFR (Not so much an issue at ORD
since visual approaches are rarely used in a non trip config). Today for example, the TStorms had enough of an impact to force a 60 rate. If you go down to a single landing runway, which can happen, your Rate will be in the high 30's. And the rule of thumb is this, when Airport Acceptance Rate is less than the demand in a given hour, flights have to be delayed somehow. If its not a lot of excess demand, the TRACONS can usually manage with miles in trail, and sometimes airborne holding. But if you get in a situation with a lot of excess demand over a period, thats when you see the ground delay programs.
At midway, the AAR
rarely changes since they can typically only take one landing airplane at a time with the two main air carrier runways crossing each other. While IFR conditions can knock out a runway in ORD
reducing the AAR
, they can't affect MDW
since they are typically only using one runway anyways. Thus weather does not have the impact on MDW
that it can on LGA
. That is why bad weather rarely affects DCA
as well, because although the airport has three runways, it basically is run as a single runway airport. Single runway airports are rarely affected by weather because of this.
For the record, I will list some airports where delays are common and what can bring the arrival rate down at each airport.
: Any sort of gusty wind or ifr will cause them to lose the Overflow runway (11-29) which is an automatic program there with all the demand in that place.
: Wind can cause the airport to go single runway, which means you have to intertwine departures which will slow the AAR
down, additionally IFR conditions can create problems:
: I haven't quite figured this airport out yet, but I do know their best config is ILS 22L while running VOR 13L at the same time. Winds and IFR will bring rates down since they can lose parallel approaches this way.
: Any sort of wet runway makes 17-35 unusable to most carriers, forcing everyone to use the long runway, bring the AAR
from either 52 or 48 (Depending on east or west ops), to 36. Also there are ceiling restrictions, but not as restrictive as some other places.
: Even in VFR conditions if the CIG is 5000 feet this place will have problems.
: If winds force any config other than 25's (i.e. 1's and 7's) this airport can be slowed down.
: Lots of things. Weather that forces anything other than X or Wierd is bad. X is least vulnerable to delays due to no crossing landing or takeoff runways while in config.