Flight number record

YX 3551

Republic Airways · Chicago to Louisville

Route: ORD → SDF
Departs: 19:40
Flights: 318
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s YX 3551, check with Republic Airways. Republic Airways flies under contract for larger airlines, so a ticket for this flight may show a different airline code and number.

YX 3551 sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 318 flights, with a median arrival 6 minutes early.

On time

74.4%

Arrivals under 15 minutes late, of 309 completed flights

Avg delay

81 min

Across delayed arrivals only, not all flights

Cancelled

2.52%

National rate is 1.81%

1 hour+ late

10.0%

National rate is 8.1%

These figures cover 318 flights between July 2025 and June 2026. Beyond the headline rate, 10.0% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Schedule

When YX 3551 flies

YX 3551 flies ORD to SDF without a single fixed slot. Its most common scheduled departure was 19:40, used on 93 of 318 flights, with 19:52 (56 flights) and 19:55 (52 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 19:4093 flights29.2%
Departs 19:5256 flights17.6%
Departs 19:5552 flights16.4%

Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.

Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.

A 19:40 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.2%, and YX 3551 runs 6 points better at 74.4%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.

Against the route

YX 3551 next to ORD to SDF

Every carrier on ORD to SDF combined arrived on time 75.3% of the time across 2,804 flights, so YX 3551 is about level with it. Republic flew 1,733 flights on the same city pair under all its flight numbers, including this one, and those ran 75.0% on time. Across its whole network Republic Airways managed 78.5%, which this flight trails by 4 points.

YX 3551 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
YX 3551thin sample	318	74.4%	81 min	2.52%	C
All Republic Airways on ORD–SDF	1,733	75.0%	75 min	3.87%	B−
All carriers on ORD–SDF	2,804	75.3%	71 min	3.32%	B−
Republic Airways, whole network	361,482	78.5%	72 min	4.08%	B−

Across the year

YX 3551 quarter by quarter

YX 3551 did not run the same all year. Its best quarter was Apr–Jun 2026 at 81.8% on time and its weakest Jan–Mar 2026 at 71.6%, a swing of 10 points on roughly 80 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Jul–Sep 202591 flights73.9%
Oct–Dec 202591 flights74.2%
Jan–Mar 202690 flights71.6%
Apr–Jun 202646 flights81.8%

Scale runs 65% to 85%. Rows with fewer than 30 flights show a dash.

By weekday, YX 3551 did best on Friday at 84.1% on time and worst on Monday at 68.2%. Each day rests on about 45 flights, so a gap of 16 points is worth noticing but could still narrow in another year.

Delay causes

Why YX 3551 runs late

One category carries most of the weight here. Late-arriving aircraft accounts for 56% of the 6,370 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
56%
Carrier
25%
National Airspace System
18%
Extreme weather
2%

56% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 6,370 reported delay minutes here, that single category outweighs weather by 33 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 6,370 delay minutes reported on YX 3551.

Cancellations run at 2.52%, against 1.81% nationally. That is about one flight in 40 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.

Connections and routes

What a delay on this flight costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.0% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

The same number turns up on five other city pairs in the data, including PWM to ORD (56), IND to EWR (24) and XNA to ORD (18), but none flew often enough under YX 3551 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to ORD to SDF only.

One caution: this is a thin sample. 318 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.

What to do with this

Booking YX 3551

For a booking, the cancellation rate is the figure to plan around on YX 3551: 2.52% of its 318 scheduled flights did not operate. A late arrival costs a little over an hour, but a cancellation costs the day, so leave a later option open.

Where to go next

A flight number here means Republic Airways’s own number as it reports to the DOT. How the figures are computed is on the methodology page.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures