The National Transportation Safety Board issued a preliminary report on a runway excursion incident involving a United Airlines 737 MAX 8 aircraft that occurred March 8, with two different accounts of conditions on the runway from the flight’s pilots.
The accident occurred as the pilots were positioning the aircraft for landing. The captain was flying and the first officer acting as pilot monitoring. The discrepancies were found in their accounts, especially on runway conditions. He remembered that the runway condition codes are 3/3/3 for Runway 26L and 26R, slipped with water, while Runway 27 was better according to him with codes of 5/5/5. The NTSB however corrected that Runway 27 was actually coded 3/3/3, contrary to what the captain expected.
When the captain asked, the first officer successfully requested a change to Runway 27, with instructions to maintain their speed up and permission granted to roll out to the runway’s end. In anticipation of this, the captain decreased the autobrake setting from 2 to 1, thereby lowering the aircraft deceleration rate when landing.
As the aircraft broke through the clouds, visibility was restored, and it now appeared that both pilots perceived the runway environment a bit differently-the captain thought the runway was dry, but the first officer indicated that it looked wet. Nevertheless, touchdown was reported as smooth and within the touchdown zone at a suitable speed.
In its conclusion, the NTSB stated the following: “Due to the perception by the captain that the runway was dry, speed brakes and autobrakes were not inactivated until five seconds after touchdown because of his desire to minimize runway time, thus minimizing passenger discomfort. Manual braking did not commence until much later, when the aircraft was 4,000 feet from the end of the runway.” This delay in reaction became critical when the captain, realizing that the runway length was getting too short, started to increase the braking pressure and tried to turn onto a taxiway. The aircraft veered off the runway, with its left main and nosewheel tires entering the grass, which finally stopped the aircraft.
The incidence has sparked questions about the decision-making process and the observance of the guidelines stipulated for United Airlines in which the guideline notes a conservative approach in assessing runway conditions along with braking strategy, which stipulates to choose the maximum auto brake setting if in doubt. This episode underlines the importance of runway condition assessments and the critical nature of decisions regarding braking in the interest of aircraft operation safety.