Flight profile · Delta Air Lines
DL639
Los Angeles (LAX) to Boston (BOS) · scheduled 7:55 AM – 4:17 PM
How DL639 performs
621 operations, December 2024 – August 2026.
Between its first and last recorded date on LAX → BOS, DL639 averaged about one operation a day or more (621 in 621 days, cancelled ones included).
DL639 arrived on time 85.1% of the time, against 80.0% for all LAX → BOS flights, so this departure is 5.1 percentage points better than the route as a whole. Against Delta Air Lines’ own flights on this route it is 4.4 points better.
Source: US DOT Bureau of Transportation Statistics · 621 operations, December 2024 – August 2026 · If DL639 is cancelled or significantly changed, DOT’s automatic refund rule may entitle you to your money back. The refund checker walks through eligibility.
Where DL639 is right now
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Against the rest of the route
| Flight or route | On time | Cancelled | Median delay | Severe | Flights |
|---|---|---|---|---|---|
| DL639 | 85.1% | 1.77% | -7 min | 4.4% | 621 |
| Delta Air Lines on LAX → BOS | 80.7% | 0.94% | -6 min | 7.0% | 3,725 |
| All LAX → BOS flights | 80.0% | 0.84% | -8 min | 7.5% | 14,792 |
DL639 cancelled 11 of 621 operations (1.77%), above the 0.84% for LAX → BOS.
4.4% of DL639’s arrivals were an hour or more late, against 7.5% across LAX → BOS, so the long delays are less common on this number than on the route.
Source: FlyerIntel analysis of US DOT BTS data · December 2024 – August 2026
Why DL639 runs late
Where US DOT attributed the delay minutes on this flight.
crew, maintenance, boarding and fueling, all within the carrier’s control
airspace and airport capacity, including weather-driven flow control
the inbound aircraft was late, so this flight started late
weather severe enough to stop this flight specifically
Share of the delay minutes US DOT attributed to each cause for DL639 on LAX → BOS. Only delays of 15 minutes or more are attributed. What the five causes mean
Source: US DOT Bureau of Transportation Statistics · Data covering December 2024 – August 2026
Does a late aircraft delay this flight?
How often the plane that flies DL639 comes in late, and what that does to the departure.
DL639 is usually the aircraft’s first flight of the day: the schedule gives it a median of 10.1 hours on the ground at LAX, so its “inbound” is mostly the aircraft’s arrival the evening before.
When the aircraft came in 15 or more minutes late, DL639 pushed back an average of 5 minutes late; when it came in on time or early, an average of 1 minute late.
Matched by tail number to the aircraft’s previous flight into LAX: 432 of 610 departures. Unknown, cancelled or diverted inbounds and gaps over 12 hours are left out.
Against the network at the same turn length
| Share of departures | Inbound landed 15+ late | Left 15+ late after a late inbound | Left 15+ late after an on-time inbound |
|---|---|---|---|
| DL639 | 35% | 8% | 7% |
| Network, same turn | 29% | 12% | 9% |
A night on the ground absorbs most of a late arrival, so a late inbound matters far less here than on a same-day turn.
The network row is every flight with a scheduled turn of 6 hours or more, usually overnight. How often DL639’s aircraft landed 15 or more minutes late is higher than the network’s and, once the aircraft was late, how often DL639 left 15 or more minutes late is lower than the network’s.
Source: US DOT Bureau of Transportation Statistics · Data covering December 2024 – August 2026
From pushback to gate
When it leaves LAX late, does that still matter by the time it reaches BOS?
DL639 pushes back an average of 7.1 minutes late and reaches the gate at BOS an average of 2.5 minutes late. The 4.5 minutes between those two figures are slack the published schedule already carries, so a late pushback is partly, not fully, made up before the gate. Its 17.2 minutes on the taxiways at LAX is about what any departure from the airport in that hour spends.
On arrival at BOS, DL639 spends 10.4 min taxiing from touchdown to the gate — ground time a connecting passenger sits through before they can even leave the aircraft, on top of however late the flight itself ran. That is 1.5 minutes longer than a typical BOS arrival (9.0 min).
Taxi-out is gate to wheels up and sits inside the scheduled block; the hourly comparison is 37,698 LAX departures. Taxi-in is landing to gate, set against 454,075 arrivals at BOS. More on taxi time.
Source: FlyerIntel analysis of US DOT BTS data · December 2024 – August 2026
The hour it leaves LAX
DL639 has one departure time, 7:55 AM, so this is what that hour at LAX is worth.
On-time arrival rate. 37,698 departures from LAX are scheduled in the 7 AM–8 AM hour over the period, against 611,647 across the whole day.
DL639 is scheduled out of LAX at 7:55 AM, in the 7 AM–8 AM bank. Departures from LAX in that hour arrive on time 88.9% of the time against 81.3% across the airport’s whole day — the slot alone is worth 7.6 points better before anything about this particular flight is considered.
Both airport figures cover every destination from LAX, so they describe the slot, not this journey; the route comparison is above. Why the hour matters.
Source: FlyerIntel analysis of US DOT BTS data · December 2024 – August 2026 · Hours below 120 departures are not scored.
Other routes DL639 has flown
Carriers reassign flight numbers. DL639 also served these 15 other city pairs in the period.
| Route | Operated | Flights | On time |
|---|---|---|---|
| LAS→ATL Las Vegas to Atlanta | November 11, 2024 – December 18, 2024 | 36 | — |
| PDX→ATL Portland to Atlanta | October 7–25, 2024 | 19 | — |
| ATL→DEN Atlanta to Denver | September 9, 2024 – October 6, 2024 | 28 | — |
| DEN→ATL Denver to Atlanta | September 9, 2024 – October 6, 2024 | 28 | — |
| LGA→MCI New York to Kansas City | August 11, 2024 – September 8, 2024 | 26 | — |
| MCI→LGA Kansas City to New York | September 8, 2024 | 1 | — |
| DTW→LAX Detroit to Los Angeles | July 13, 2024 – August 24, 2024 | 6 | — |
| IAD→SEA Washington to Seattle | September 5, 2023 – June 6, 2024 | 115 | 79.3% |
| SLC→SEA Salt Lake City to Seattle | April 11, 2024 – May 6, 2024 | 16 | — |
| ORF→ATL Norfolk to Atlanta | March 10, 2024 – April 8, 2024 | 30 | — |
| ATL→HOU Atlanta to Houston | December 16–30, 2023 | 13 | — |
| HOU→ATL Houston to Atlanta | December 16–30, 2023 | 13 | — |
| MCO→MIA Orlando to Miami | December 7–15, 2023 | 9 | — |
| MIA→MCO Miami to Orlando | December 7–15, 2023 | 9 | — |
| LAX→ATL Los Angeles to Atlanta | July 1, 2023 – September 4, 2023 | 66 | — |
The figures above describe only LAX → BOS, the route DL639 flies now.
When it goes wrong
The average describes a usual day. This is the day that ruins a connection.
24 min late
against a median of 7 min early
Percentiles over 621 operations; cancelled and diverted flights are counted separately.
Source: US DOT Bureau of Transportation Statistics · Data covering December 2024 – August 2026
Other flights on this route
Same airports, same journey, different odds of arriving on time.
| Flight | Airline | On time | Median arrival | Operations |
|---|---|---|---|---|
| UA2210 | United Airlines | 89.0% | 12 min early | 796 |
| DL639 this flight | Delta Air Lines | 85.1% | 7 min early | 621 |
| AA2453 | American Airlines | 84.1% | 8 min early | 1,052 |
| UA1783 | United Airlines | 83.5% | 12 min early | 796 |
| DL507 | Delta Air Lines | 81.5% | 5 min early | 709 |
| B6288 | JetBlue | 80.9% | 10 min early | 1,083 |
| B6188 | JetBlue | 74.8% | 6 min early | 637 |
| B6988 | JetBlue | 74.6% | 7 min early | 1,018 |
| DL437 | Delta Air Lines | 74.3% | 4 min early | 710 |
Among the 9 departures listed, DL639 has the 2nd highest on-time rate, 3.9 points behind the best. Every departure here has at least 600 operations; the other rows are the most punctual on the route, not all of them.
Data and methodology
Calculated by FlyerIntel from 621 records of DL639 operating LAX → BOS, published by the US DOT Bureau of Transportation Statistics. A flight counts as delayed when it arrives 15 or more minutes after schedule; cancelled and diverted flights are reported separately, not in the on-time rate.
Full methodology · Data sources · Report a problem
Related research: Most and Least Reliable Flight Numbers · The Delay You Inherit · Making Up Time in the Air
Analysis last recomputed