74% of flights leaving Islip (ISP) arrived on time over the past 12 months, 2 points worse than the national average of 76%. About 14 flights leave ISP on a typical day; 2.2% were cancelled. 73% pushed back from the gate on time, so most of the lateness is already there when the flight leaves the gate.
At a glance
- Best hour to fly: 6 a.m. (88% on time). Worst: 5 p.m. (61%).
- Best month: October (87%). Worst: August (69%).
- Most reliable airline here: Southwest Airlines (77%), vs JetBlue at 70%.
- Biggest delay cause: late-arriving aircraft (43% of delay minutes).
- Year on year: getting worse (77% → 74%).
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for flights leaving ISP: when a flight was late, it was under 45 minutes late 54% of the time. About 1 in 12 flights landed an hour or more late, and 1 in 56 three hours or more; 2.2% were cancelled outright.
- On time or early74%
- 15–30 min late8.7%
- 30–60 min late7.0%
- 1–2 hours late4.7%
- 2–3 hours late1.7%
- 3+ hours late1.8%
- Diverted0.4%
- Cancelled2.2%
Share of all 5,016 scheduled flights, past 12 months, by arrival time against schedule.
Best time of day to fly out of ISP
Time of day matters more at ISP than almost anything else you control. Flights scheduled to leave at 6 a.m. arrived on time 88% of the time; at 5 p.m. it was 61%, a 27-point gap. Taken together, early departures (5–9 a.m.) ran 85% on time against 61% for the evening bank (5–10 p.m.). Early planes usually start the day at the airport, so they haven't had a chance to pick up delays elsewhere. By evening a late inbound aircraft, a crew running out of duty hours or an afternoon thunderstorm can push one late flight into the next.
Hour × month
Combine the two and the spread is wider still. The most reliable combination at ISP was a 6 a.m. departure in October (97% on time); the least, 5 p.m. in March (50%). If you can only move one thing, move the hour. Departure hour usually shifts the odds more than the month does.
Each cell: on-time rate for that departure hour in that calendar month, 2023–2026. Find your travel month, then look along the row for the greenest hour.
Best and worst months
August is the hardest month at ISP, with 69% of flights on time across 2023–2026; October is the best at 87%. Summer (June–August) runs 12 points worse than autumn: heavy schedules, peak loads and afternoon thunderstorms. Winter costs 11 points against autumn. Cancellations peak in February (2.9% of flights).
Airlines at ISP
Southwest Airlines runs 52% of departures from ISP, so ISP is effectively its hub. When Southwest Airlines has a bad day, so does the airport. Among airlines with at least 1,000 departures here, Southwest Airlines was the most reliable (77% on time) and JetBlue the least (70%), a 7-point difference. On a route where both fly, that difference is worth more than a small fare gap.
| Airline | Departures | On time | Left on time | Cancelled | Typical arrival |
|---|---|---|---|---|---|
| Southwest Airlines | 2,586 | 77% | 73% | 1.6% | −3 min |
| JetBlue | 1,600 | 70% | 74% | 2.4% | −5 min |
| Frontier Airlines | 830 | 71% | 72% | 3.6% | −9 min |
Why flights are late at ISP
Airlines report a cause for every flight that arrives 15 or more minutes late. At ISP, 43% of delay minutes came from late-arriving aircraft: the plane showed up late from its previous flight, so the delay started somewhere else. Next is the airlines themselves at 27%. That's why the first flight of the morning is the safest bet: it has no earlier flight to inherit a delay from. Of the 109 cancellations, 62% were blamed on weather.
The average taxi from gate to takeoff is 13 minutes, shorter than at most large U.S. airports.
ISP vs nearby airports
ISP isn't the only option in New York. Over the past year JFK ran 71% on time with 4.3% of flights cancelled; LGA ran 68% on time with 5.3% of flights cancelled; EWR ran 74% on time with 3.6% of flights cancelled; HPN ran 71% on time with 3.8% of flights cancelled, against 74% and 2.2% at ISP. There's little to choose between them on reliability; pick on fares and convenience.
| Airport | Distance | Departures | On time | Cancelled |
|---|---|---|---|---|
| ISP Long Island MacArthur | — | 5,016 | 74% | 2.2% |
| HPN Westchester | 37 mi | 12,438 | 71% | 3.8% |
| JFK New York JFK | 37 mi | 124,887 | 71% | 4.3% |
| LGA LaGuardia | 40 mi | 166,553 | 68% | 5.3% |
| EWR Newark | 56 mi | 134,823 | 74% | 3.6% |
Month by month
Over the latest 12 months 74% of ISP departures were on time, against 77% in the 12 months before, a decline of 3 points. The best recent month was October 2025 (84%); the worst, December 2025 (63%).
Worst cancellation days
The worst single day in the past year was Monday, Feb 23, 2026, when 100% of 18 scheduled departures were cancelled. Days like that are usually a major storm, a system outage or a holiday peak hitting bad weather. No average predicts them, so on a stormy forecast, check your airline's travel waivers.
| Date | Departures | Cancelled | On time |
|---|---|---|---|
| Feb 23, 2026 | 18 | 100% | 0% |
| Jan 25, 2026 | 15 | 87% | 7% |
| Mar 16, 2026 | 15 | 73% | 20% |
| Feb 24, 2026 | 12 | 50% | 25% |
| Jan 26, 2026 | 13 | 46% | 23% |
| Dec 27, 2025 | 19 | 32% | 21% |
| Jul 18, 2026 | 16 | 31% | 38% |
| Feb 22, 2026 | 17 | 29% | 29% |
| Jul 21, 2026 | 13 | 23% | 38% |
| Nov 30, 2025 | 16 | 13% | 50% |
Last flights of the day
The last flight of the day is a different bet. Across routes from ISP, each airline's final departure was cancelled 2.5% of the time, against 1.7% for its earlier flights (1.4× as often). Late in the day crews run short on duty hours, aircraft arrive late from elsewhere, and with no later flight to fold passengers into, cancelling is easier for the airline. 2.7% of last flights landed 3+ hours late. The riskiest last flight out was Southwest Airlines to Baltimore (2.5% cancelled).
| Last flight to | Airline | Leaves | Cancelled | 3h+ late | On time |
|---|---|---|---|---|---|
| BWI Baltimore | Southwest Airlines | 4:40 p.m. | 2.5% | 3.0% | 74% |
| PBI West Palm Beach | JetBlue | 2:40 p.m. | 3.4% | 1.9% | 67% |
| MCO Orlando | Southwest Airlines | 5:15 p.m. | 1.4% | 2.8% | 53% |
| PBI West Palm Beach | Southwest Airlines | 11:10 a.m. | 1.7% | 2.2% | 57% |
Each airline's last scheduled departure of the day on a route, on days it flies the route at least twice; past 12 months. Riskiest first.
Tips for flying out of ISP
- Book the earliest departure you can live with. At ISP the 6 a.m. flights do best.
- Traveling in August? Leave extra slack for anything that can't move: cruises, weddings, the last connection of the day.
- Choosing between airlines? Southwest Airlines has the better record here.
- Need to arrive tonight? Don't book the last flight out of ISP; the one before it leaves you a backup.
- Delayed already? Most delays at ISP come from late-arriving aircraft. If your inbound plane is late, your flight will be too, whatever the board says.
Routes from ISP
Where you're going matters too. From ISP, the most reliable busy route was to Baltimore (BWI, 84% on time) and the least reliable to West Palm Beach (PBI, 70%). Flights into congested airports inherit their delays: an air traffic program at the destination holds planes on the ground here.
Least reliable first. Routes with at least 365 flights a year.
| To | Flights | On time | Cancelled | Typical arrival |
|---|---|---|---|---|
| FLL Fort Lauderdale | 418 | 67% | 1.9% | −4 min |
| TPA Tampa | 433 | 68% | 3.9% | −3 min |
| PBI West Palm Beach | 1,133 | 70% | 2.3% | −1 min |
| MCO Orlando | 1,442 | 72% | 1.9% | −4 min |
| BWI Baltimore | 1,259 | 84% | 1.5% | −7 min |
Flights into ISP
Arriving rather than leaving? These are the routes into Long Island MacArthur, least reliable first. The weakest is from Fort Lauderdale (66% on time).
| From | Flights | On time | Cancelled |
|---|---|---|---|
| FLL Fort Lauderdale | 419 | 66% | 2.1% |
| PBI West Palm Beach | 1,134 | 72% | 1.8% |
| TPA Tampa | 430 | 73% | 2.8% |
| MCO Orlando | 1,441 | 75% | 1.7% |
| BWI Baltimore | 1,260 | 76% | 1.9% |
Questions about ISP delays
What is the best time to fly out of ISP?
Flights scheduled at 6 a.m.: over the past year 88% of ISP departures at that hour arrived on time, against 61% at 5 p.m., the worst hour.
What month has the most flight delays at ISP?
August (69% on time). October is the best month (87%).
Which airline is most on time at ISP?
Southwest Airlines: 77% of its ISP departures arrived on time over the past year. JetBlue had the weakest record at 70%.
Why are flights delayed at ISP?
The biggest cause was late-arriving aircraft (43% of delay minutes): the plane showed up late from its previous flight, so the delay started somewhere else. Then the airlines themselves (27%).
Is ISP or JFK or LGA or EWR or HPN more reliable?
Over the past year: ISP 74% on time, JFK 71%, LGA 68%, EWR 74%, HPN 71%.
How often are flights cancelled at ISP?
2.2% of scheduled departures over the past 12 months, peaking in February at 2.9%.
Hours are scheduled local departure times. "On time" means arriving less than 15 minutes late at the destination; cancelled and diverted flights count as not on time. Method.