Originally Posted by
cepheid
The "scheduled" time is block-to-block, i.e. from pushback at the origin gate to blocking at the arriving gate. This includes time for taxi and possible slot delays, which are common in the busier airports (JFK, for example). UA has to account for that in the total transit time, because there's no point quoting an airborne time of 1:46 when taxi and slot delays can add another 30-45 mins.
Also, note that the "on time" designation refers only to getting the flight out... it doesn't refer to arrival, although certainly a late departure has a higher risk of late arrival (and therefore a late departure for the next flight).
There are "on time departures" and "on time arrivals", which I think is defined as arrival at gate no more than 15 minutes behind the schedule. I think the DOT exercises some control/influence on US carriers to make sure that their published schedules are reasonable given flight history, i.e. each flight number should not operate as late arrivals too much of the time (not sure of the definition DOT uses). It's a sort of truth in advertising, i.e. don't say you can make it from ORD to LGA in 1:30 at 5:00pm when you know that taxi and slot delays mean it's really more like 2:30 most of the time. You will see the same route (and same or similar equipment) showing somewhat different block-to-block times at different times of day. In my experience these do not vary as much as they really should, but they do vary in the right way (longer at peak times, shorter at non-peak).
Looking at today's schedule for ORD-LGA, departures from 7:00am to 8:50pm, the following are the scheduled block times:
2:06
2:08
2:13
2:10
2:11
2:18
2:16
2:21
2:27
2:24
2:21
2:21
2:01
You can see the increases in the morning and afternoon rush times. The shortest actual times ran about 1:55 this weekend so the afternoon peak has about a half hour extra time built in.
Charles