Flight profile · Delta Air Lines
DL977
Boston (BOS) to San Francisco (SFO) · scheduled 7:55 AM – 11:37 AM
How DL977 performs
893 operations, July 2023 – July 2026.
DL977 arrived on time 80.8% of the time, against 74.6% for all BOS → SFO flights, so this departure is 6.2 percentage points better than the route as a whole. Against Delta Air Lines’ own flights on this route it is 7.2 points better.
Source: US DOT Bureau of Transportation Statistics · 893 operations, July 2023 – July 2026 · If DL977 is cancelled or significantly changed, DOT’s automatic refund rule may entitle you to your money back. The refund checker walks through eligibility.
Where DL977 is right now
A live reading, only if you ask for it. It is not part of the reliability record above.
Ask for the position of DL977 right now, if receivers on the ground are hearing it. Nothing is requested until you press the button.
Against the rest of the route
| Flight or route | On time | Cancelled | Median delay | Severe | Flights |
|---|---|---|---|---|---|
| DL977 | 80.8% | 0.67% | -8 min | 5.0% | 893 |
| Delta Air Lines on BOS → SFO | 73.6% | 0.91% | -6 min | 7.8% | 2,529 |
| All BOS → SFO flights | 74.6% | 1.03% | -6 min | 8.8% | 14,232 |
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
Why DL977 runs late
Where US DOT attributed the delay minutes on this flight.
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
Share of the delay minutes US DOT attributed to each cause for DL977 on BOS → SFO. Only delays of 15 minutes or more are attributed.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
Does a late aircraft delay this flight?
How often the plane that flies DL977 comes in late, and what that does to the departure.
When the aircraft came in 15 or more minutes late, DL977 pushed back an average of 47 minutes late; when it came in on time or early, an average of 4 minutes late.
Each departure is matched to the flight the same aircraft flew into BOS just before it, using the tail number in the DOT file, 789 of 887 departures in all. A departure is left out when that flight is unknown, was cancelled or diverted, or the aircraft had sat for more than 12 hours. A flight the airline cancelled never left and is not in the count, and one flown by a substitute aircraft is matched to the aircraft that flew it, not to the one first planned.
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 |
|---|---|---|---|
| DL977 | 17% | 61% | 12% |
| Network, same turn | 17% | 68% | 9% |
The schedule leaves a normal turn: enough time to clean and board if the aircraft is on time, little to spare if it is not.
The network row is every flight with a scheduled turn of 60 to 89 minutes. How often DL977’s aircraft landed 15 or more minutes late is about the same as the network’s and, once the aircraft was late, how often DL977 left 15 or more minutes late is lower than the network’s.
More: Which Flight Numbers Pay for a Late Aircraft lists the flight numbers that pass a late aircraft on.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
From pushback to gate
When it leaves BOS late, does that still matter by the time it reaches SFO?
DL977 pushes back an average of 12.9 minutes late and reaches the gate at SFO an average of 0.5 minutes early. The 13.4 minutes between those two figures are slack the published schedule already carries, which is why a late pushback on this flight does not reliably become a late arrival. It spends 23.9 minutes on the taxiways at BOS, 1.6 minutes longer than a typical BOS departure in the same hour.
On arrival at SFO, DL977 spends 7.7 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 about what any arrival at SFO spends on the ground before reaching the gate.
Departure delay is averaged over every pushback and arrival delay over every completed arrival, so the two counts differ by the flights that never reached SFO. Taxi-out is gate to wheels up and sits inside the scheduled block rather than on top of it; the comparison is 43,804 departures from BOS scheduled in the clock hour DL977 most often leaves in. Taxi-in is landing to gate, compared against every arrival FlyerIntel has on file at SFO (436,060 flights), not just DL977’s own. More on taxi time.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026
The hour it leaves BOS
Part of any flight’s record belongs to the clock rather than to the flight. DL977 has one departure time, so this is what that time is worth.
On-time arrival rate. 43,804 departures from BOS are scheduled in the 7 AM–8 AM hour over the period, against 440,893 across the whole day.
DL977 is scheduled out of BOS at 7:55 AM, in the 7 AM–8 AM bank. Departures from BOS in that hour arrive on time 85.5% of the time against 77.2% across the airport’s whole day — the slot alone is worth 8.3 points better before anything about this particular flight is considered.
The two airport figures cover every departure from BOS to every destination, so they describe the slot rather than this journey — the like-for-like comparison against the route is above. Hours are scheduled local, and a number whose schedule moved between banks inside the period has no single hour and is not described here at all. Why the hour matters.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Hours below 120 departures are not scored.
By day of week
Does DL977 run worse on particular days?
Thursday is historically the most reliable day and Friday the least, a gap of 9.7 percentage points.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Days with fewer than 120 operations are not scored.
Other routes DL977 has flown
A flight number is a slot in a schedule, and carriers reassign it. These are the other city pairs this number served in the analysis period.
| Route | Operated | Flights | On time |
|---|---|---|---|
| SFO→BOS San Francisco to Boston | July 1, 2023 – July 31, 2026 | 829 | 71.6% |
| MCO→ATL Orlando to Atlanta | August 11, 2025 – December 19, 2025 | 130 | 64.3% |
| DSM→ATL Des Moines to Atlanta | June 14, 2025 – August 9, 2025 | 15 | — |
| ATL→DSM Atlanta to Des Moines | July 12, 2025 – August 9, 2025 | 5 | — |
| SRQ→ATL Sarasota/Bradenton to Atlanta | December 21, 2024 – January 4, 2025 | 3 | — |
Because the same number has served different journeys, the statistics above describe only the route DL977 currently operates. Blending them would produce an average of two different flights.
When it goes wrong
The average describes a usual day. This is the day that ruins a connection.
35 min late
against a median of 8 min early
Percentiles over 893 operations; cancelled and diverted flights are counted separately.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
Other flights on this route
Same airports, same journey, different odds of arriving on time.
| Flight | Airline | On time | Median arrival | Operations |
|---|---|---|---|---|
| UA1008 | United Airlines | 88.0% | 12 min early | 954 |
| B61333 | JetBlue | 84.3% | 12 min early | 601 |
| UA1187 | United Airlines | 81.0% | 12 min early | 604 |
| DL977 this flight | Delta Air Lines | 80.8% | 8 min early | 893 |
| B6133 | JetBlue | 80.2% | 10 min early | 660 |
| B61833 | JetBlue | 79.3% | 12 min early | 712 |
| AS357 | Alaska Airlines | 68.6% | 2 min early | 636 |
| DL475 | Delta Air Lines | 68.4% | 3 min early | 744 |
| B6733 | JetBlue | 68.2% | 3 min early | 794 |
Every departure listed carries at least 600 operations, so the comparison is between figures that mean something. DL977 is placed in the same ordering rather than left out of it; the rows around it are the most punctual departures on the route, not all of them, so this is a comparison and not a rank. Schedules change; confirm the departure still operates before booking around this.
Data and methodology
Calculated by FlyerIntel from 893 records of DL977 operating BOS → SFO, 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 excluded from the on-time rate and reported separately. Flight numbers are resolved as carrier plus number plus route, because the same number serves different routes over time.
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