- Location: Houston, Texas
- Accident Number: DCA25LA025
- Date & Time: October 24, 2024, 12:52 Local
- Registration: N27515
- Aircraft: Boeing 737-9
- Aircraft Damage: Substantial
- Defining Event: Aircraft structural failure
- Injuries: 145 None
- Flight Conducted Under: Part 121: Air carrier - Scheduled
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/195444/pdf
https://data.ntsb.gov/Docket?ProjectID=195444
United Airlines flight 1181 experienced a failure of the number 3 and number 4 tires on the right main landing gear (MLG) during landing on runway 26L at George Bush Intercontinental/Houston Airport (IAH), Houston, Texas. The airplane exited the runway and stopped on a high-speed taxiway, and the passengers were deplaned and bussed to the terminal. Post landing inspection revealed substantial damage to the aircraft fuselage skin.
The captain was the pilot flying and the first officer (FO) was the pilot monitoring for the entire duration of the flight. During preflight preparations for departure from Harry Reid International Airport (LAS), Las Vegas, Nevada, both pilots reviewed the flight release and noted three Minimum Equipment List (MEL) items: the autobrake system, the antiskid system, and a coffee maker. The autobrake and antiskid systems had been deferred earlier that morning due to maintenance issues, specifically an antiskid alert light that failed to test correctly.
Given these deferrals, the crew stated they reviewed the enroute and destination weather conditions and reviewed operational limitations with the MEL items. Weather was visual flight rules (VFR) at both departure and destination airports. The crew determined that all MELrelated limitations were satisfied, including the need for a dry runway, no tailwind, use of flaps 40 for landing, and sufficient landing distance. The aircraft departed LAS without incident.
During descent into Houston, the crew stated they conducted the approach briefing, incorporating the limitations due to the MEL items. The FO noted a slight tailwind component on Runway 26L and requested an opposite-direction landing due to the autobrake and antiskid systems not available. However, Houston approach air traffic control (ATC) was unable to accommodate the request due to traffic volume and airspace restrictions. Winds were later reported as calm, and the crew proceeded with a visual approach to Runway 26L. When the FO did a final wind check with the tower, they were informed of a direct left-to-right crosswind relative to the runway, at 8 knots.
Both the captain and FO described the landing as soft and initially uneventful. The speed brakes deployed automatically, and the captain stated he applied brakes and activated the thrust reversers. However, shortly after the reversers were deployed, the captain perceived an abnormal condition, suspecting a tire failure due to the unusual noise and slight lateral swaying. The FO described the sensation as skidding followed by grinding and noted that the aircraft did not roll smoothly below 10 knots, with a right-wing-down lean. The captain suspected a blown tire and steered the aircraft off the runway and onto a high-speed taxiway.
A review of the FDR data for the landing show that as the pitch angle was reduced, the brake pressure began to rise to about 500 psi, prior to the right MLG air/ground switch changing to “ground”. After the right MLG was on the ground, the brake pressure continued to rise, peaking at about 1500 psi as the left MLG air/ground switch changed to “ground”. Brake pressure then eased to about 1000 psi as the nose gear air/ground switch changed to “ground” and the vertical acceleration peaked at about 1.3g. About one second later, there was a second spike in vertical acceleration to 1.3g, concurrent with an increased roll attitude to about 2 degrees right wing down, consistent with the failure of the right MLG tires.
Since the autobraking and antiskid systems were disabled, the flight crew had to manually apply brakes during the landing. The FDR data showed that the brake application happened before all three landing gear had changed to “ground” status, and likely before the wheels had an opportunity to fully spin up. The early application of the brakes during the landing likely contributed to the failure of the tires on the right MLG.
The ATC tower reported seeing smoke emanating from the aircraft during rollout, prompting the crew to request emergency vehicles. Upon stopping, ground personnel confirmed that both tires on the right MLG were severely damaged. The crew started the auxiliary power unit (APU), shut down the engines, and completed the after-landing and parking checklists. Passengers were informed of the situation and deplaned via air stairs approximately 40–45 minutes after landing. Buses transported all passengers and crew to the terminal. No injuries were reported.
Post landing inspection showed an impact dent on the fuselage above the right MLG. The affected area is identified in the United Airlines structural repair manual (SRM) as a principal structural element and required repair utilizing the techniques identified in the SRM. Inspection of the frames, stringers, and shear ties near the damaged area showed no damage to any adjacent areas.
- Probable Cause: Brake application before all three landing gears were on the ground, which caused the failure of the right main landing gear tires and resulted in tire fragments impacting the fuselage.
