Flight UA2121
United Airlines flight UA2121
Looking for UA2121 in the airâŚ
Alerts at this flight's airports
Denver (DEN) to Grand Rapids (GRR)
Historically, this flight arrives 15+ minutes late 32% of the time, and when it is late the delay averages 77 minutes. It was cancelled 0.8% of the time.
- On-time arrivals
- 68.2%
- Less than 15 minutes late
- Cancelled
- 0.8%
- Of scheduled flights
- Average delay when late
- 77 min
- Flights arriving 15+ minutes late
- Flights tracked
- 237
- Scheduled flights in the period
What caused the delays
- Late-arriving aircraft 62%
- Air traffic control & airport 21%
- Airline (crew, maintenance, cleaning) 14%
- Extreme weather 4%
- Security 0%
Share of delay minutes airlines attributed to each cause (BTS).
Seattle (SEA) to San Francisco (SFO)
Historically, this flight arrives 15+ minutes late 87% of the time, and when it is late the delay averages 73 minutes. It was cancelled 1.9% of the time.
- On-time arrivals
- 13.5%
- Less than 15 minutes late
- Cancelled
- 1.9%
- Of scheduled flights
- Average delay when late
- 73 min
- Flights arriving 15+ minutes late
- Flights tracked
- 53
- Scheduled flights in the period
What caused the delays
- Air traffic control & airport 77%
- Airline (crew, maintenance, cleaning) 23%
- Late-arriving aircraft 0%
- Extreme weather 0%
- Security 0%
Share of delay minutes airlines attributed to each cause (BTS).
San Francisco (SFO) to Denver (DEN)
Historically, this flight arrives 15+ minutes late 50% of the time, and when it is late the delay averages 31 minutes. It was cancelled 0.0% of the time.
- On-time arrivals
- 50.0%
- Less than 15 minutes late
- Cancelled
- 0.0%
- Of scheduled flights
- Average delay when late
- 31 min
- Flights arriving 15+ minutes late
- Flights tracked
- 53
- Scheduled flights in the period
What caused the delays
- Late-arriving aircraft 42%
- Air traffic control & airport 31%
- Airline (crew, maintenance, cleaning) 27%
- Extreme weather 0%
- Security 0%
Share of delay minutes airlines attributed to each cause (BTS).
Kalispell (FCA) to Denver (DEN)
Historically, this flight arrives 15+ minutes late 15% of the time, and when it is late the delay averages 83 minutes. It was cancelled 0.0% of the time.
- On-time arrivals
- 84.6%
- Less than 15 minutes late
- Cancelled
- 0.0%
- Of scheduled flights
- Average delay when late
- 83 min
- Flights arriving 15+ minutes late
- Flights tracked
- 52
- Scheduled flights in the period
What caused the delays
- Late-arriving aircraft 87%
- Air traffic control & airport 9%
- Airline (crew, maintenance, cleaning) 4%
- Extreme weather 0%
- Security 0%
Share of delay minutes airlines attributed to each cause (BTS).
Newark (EWR) to Denver (DEN)
Historically, this flight arrives 15+ minutes late 42% of the time, and when it is late the delay averages 62 minutes. It was cancelled 0.0% of the time.
- On-time arrivals
- 58.1%
- Less than 15 minutes late
- Cancelled
- 0.0%
- Of scheduled flights
- Average delay when late
- 62 min
- Flights arriving 15+ minutes late
- Flights tracked
- 31
- Scheduled flights in the period
What caused the delays
- Late-arriving aircraft 45%
- Airline (crew, maintenance, cleaning) 37%
- Air traffic control & airport 18%
- Extreme weather 0%
- Security 0%
Share of delay minutes airlines attributed to each cause (BTS).
Dulles (IAD) to Denver (DEN)
Only 19 flights on record, which is too few for reliable odds.
- On-time arrivals
- 78.9%
- Less than 15 minutes late
- Cancelled
- 0.0%
- Of scheduled flights
- Average delay when late
- 72 min
- Flights arriving 15+ minutes late
- Flights tracked
- 19
- Scheduled flights in the period
What caused the delays
- Late-arriving aircraft 64%
- Air traffic control & airport 34%
- Airline (crew, maintenance, cleaning) 2%
- Extreme weather 0%
- Security 0%
Share of delay minutes airlines attributed to each cause (BTS).
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Show as table
| Month | On time | Flights |
|---|---|---|
| September 2025 | 100.0% | 6 |
| October 2025 | 58.1% | 31 |
| November 2025 | 96.6% | 29 |
| December 2025 | 67.7% | 31 |
| January 2026 | 63.3% | 31 |
| February 2026 | 67.9% | 28 |
| March 2026 | 63.9% | 37 |
| April 2026 | 46.7% | 90 |
| May 2026 | 53.6% | 71 |
| June 2026 | 70.0% | 30 |
| July 2026 | 62.1% | 30 |
| August 2026 | 56.7% | 31 |
Source: U.S. DOT Bureau of Transportation Statistics on-time data, September 2025 â August 2026. Covers flights operated by reporting U.S. carriers. About our data