So I was looking at flights on 5/29, trying to decide on my return from ORD to EWR. Because it was about $100 cheaper, I booked the AA flight leaving at 7:30 PM, over the CO flight leaving at the same time.

On closer inspection, I noticed something very odd. The CO & AA flights have the same departure time, but the CO flight's scheduled arrival time is 27 minutes later.

5/29/08 EWR-ORD AA 1918 7:30 - 10:35, service with an MD-80
5/29/08 EWR-ORD CO 1162 7:30 - 11:02, service with a 737-500

So what's the explanation here? Is an AA MD-80 that much faster than a CO 735? Does AA get a faster clearance at ORD to get airborne? Anyone?

When your main hub is Newark, you need all the tricks in the world to give the illusion of reasonable on-time performance.

Probably different levels of padding for taxi time and delays. One airline might have gates closer to runways, or have other ways to avoid ground congestion.

Think the better question is

Does one airline pad their times much more so they have a better online percentage?

From http://www.bts.gov/xml/ontimesummary...maryFlightData

On-time Performance: January 1, 2008 - March 31, 2008
AA: 33.33%
CO: 45.07%

When compared to AA:
CO's Average Departure delay: 4.89 minutes longer
CO's Average Taxi-out time: 4.64 minutes longer
CO's Average Airborne time: 0.24 minutes longer
CO's Average Taxi-in time: 2.85 minutes longer
---
Total: CO flight takes 12.62 minutes longer, on average.

However, the 27 minutes of additional padding in the schedule gave them a significantly better on-time performance over this period.

Probably, but it's a legitimate decision, IMHO. They are making a tradeoff. By padding their schedules they appear to take longer to get from Point A to B, which puts them at a competitive disadvantage for travelers who value speed. But in doing so, they appeal more to travelers who value reliability.

I for one care more about arriving when I expect to, especially when making connections. You'd have to have a difference of 45 minutes or more before I'd care about a difference in schedule. (Unless we are talking about a very short segment like LGA-DCA, e.g.)

The problem is that on-time performance of an airline isn't readily noticeable when you purchase a ticket, whereas scheduled gate-to-gate time is. But most people would choose on price anyway.