Boeing 737-9 accident near Denver, Colorado, September 30, 2023

The NTSB's narrative final · quoted from the NTSB record

United Airlines flight 329 conducted a rejected takeoff after experiencing abnormal acceleration while on Runway 16R at Denver International Airport (DEN), Denver, Colorado. The flight was a regularly scheduled passenger flight to Boston Logan International Airport (BOS), Boston, Massachusetts. As a result of a subsequent brake fire following the rejected take off, the aircraft suffered substantial damage. No injuries were reported. The flight crew reported that before the flight, the captain and the first officer (FO) met to review the flight plan, maintenance documents, weather, and Notice to Airmen (NOTAMS). It was then that the captain noticed that the airplane had just come out of maintenance. The flight crew reported that the airplane would be close to maximum takeoff weight, and that the temperature would be high, and the flight would be taking off on runway 16R. Airport operations made runway 16R the designated runway for departures that day since it is the longest runway at DEN, with a length of 16,000 feet. Once the flight crew were onboard the airplane they reviewed the takeoff performance data where they noticed that the planned takeoff weight was more than what would be allowed for a takeoff from runway 16R. The weight at the gate was 172,800 lbs. but needed to be below 171,700 lbs. for a safe takeoff, taking into consideration the atmospheric conditions at the time. The captain reported making a call to dispatch where he spoke with a different dispatcher than the one who had created the original flight plan. The original flight plan had been created using a lower temperature of 29 Celsius which had been correct at the time, but the temperature had since risen to 31 Celsius. The new dispatcher sent 3 flight plan revisions. The flight crew reported that the first revision removed 1,000 lbs. of cargo, but did not remove enough weight to be within limits, and a second flight plan revision was requested. The second revision removed another 1000 lbs. by removing 8 passengers. The flight crew mentioned to dispatch that there was about 1000 lbs. of extra fuel onboard that could be burned off with an extended taxi, and dispatch sent a new revision to the flight plan that required an extended taxi to burn off the 1,000 lbs. of excess fuel to reduce the takeoff weight instead of removing passengers. The flight crew reported experiencing a normal pushback before preforming a “long slow” taxi to the runway with the power elevated while applying additional braking to burn more fuel. Once reaching the runway, the flight held there for an additional 10 to 15 minutes with the parking brake set to burn the additional fuel. The pilots reported that they never had any indication that the brakes were getting hot, and the Boeing 737 has no brake temperature monitoring system to inform the flight crew of brake temperatures. The flight crew commented that every other Boeing aircraft they have flown had a brake temperature monitoring system. Once below the required weight requirement, the flight crew notified Air Traffic Control (ATC) and were subsequently cleared for takeoff. The captain was the pilot flying and reported quickly noticing the aircraft not accelerating normally during the takeoff roll. He immediately rejected the takeoff and the FO informed tower. The tower then observed and notified the flight crew that there was smoke and fire on the right side of the airplane. The flight crew had no indication of fire in the cockpit. The captain then requested Aircraft Rescue and Fire Fighting (ARFF) and declared an emergency with ATC. ARFF fought the fire by releasing fire retardant on both main gear while the FO ran through the rejected takeoff checklist. The captain coordinated with the flight attendants to ensure the safety of all passengers. The captain reported making multiple public announcements (PA) to the passengers to inform them of the situation. After all appropriate checklists were complete, the captain decided against immediate evacuation based on communications with ARFF and the passengers disembarked via the air stairs that were provided by airport operations. The passengers were then driven back to the passenger terminal in buses. Postaccident investigation of the airplane revealed that the No. 1 and 2 tires had deflated. Number 3 and 4 tires had separated from the wheel assembly and there was evidence that tire fragments had impacted the airframe in several areas. The number 3 wheel assembly scraped the runway and had ground down with about 1/3 of the assembly missing, the number 4 wheel assembly was ground down to about half, and the number 2 engine nacelle had scraped the runway. In addition, several panels of the wing to body (WTB) fairing panels had suffered heat damage and tire debris was imbedded in the inner face of the engine inlet inner barrel acoustic panel. The right horizontal stabilizer also received structural damage.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.