Southwest Airlines Flight 554

During initial climbout shortly after takeoff, Southwest Airlines flight 554 struck and ingested a bird into its No. 1 (left) engine, resulting in damage to the left engine fan blades and a partial loss of engine power. The airplane began to “shake violently with a distinct loss of thrust” in the left engine. The engine master caution activated, and the captain reported that he heard the fire bell sound. The captain called for the Engine Fire or Engine Severe Damage or Separation checklist on the Quick Reference Card (QRC). According to the captain, after the first officer (FO) started the checklist, the cockpit began to fill with “acrid white smoke.” The FO called out “masks,” the pilots donned their masks, and they resumed performance of the checklist. The flight crew declared an emergency to air traffic control and requested airport rescue and firefighting (ARFF) in preparation for the flight’s return to the departure airport. The flight crew notified the cabin crew and passengers about the emergency. The captain later reported that, due to the smoke, his instrument panel was difficult to see and that he thought he might need to fly the airplane by solely using the heads-up guidance system. However, the captain stated that the smoke began to rapidly dissipate after the FO pulled the engine fire switch. After flight 554 landed and came to a full stop, ARFF personnel inspected the airplane before the flight crew taxied to the assigned gate. The passengers deplaned normally, and no injuries were reported. Postaccident examination found that the smoke in the cockpit was a result of the activation of the No. 1 engine’s load reduction device (LRD) after the bird ingestion. LRD activation is designed to reduce the severity of the vibration transmitted into the airframe by disconnecting the left engine’s fan blades from the turbomachinery. When the LRD activated, tubes supplying oil to the engine sump became dislodged and the flange from the sump area opened, allowing engine oil to enter the core compressor upstream of the pneumatic bleed ports that supply bleed air to the cabin and cockpit. The oil was exposed to high temperatures and resulted in smoke and fumes that were then fed into the cockpit. About 15 seconds after the bird ingestion, the left engine’s core speed (N2) was below 62% rpm, which would have de-energized the engine’s running relay and subsequently closed the pressure regulating shutoff valve (PRSOV). Following the closure of the PRSOV, which was the point of access into the cockpit, the smoke and fumes would have quickly dissipated. Considering that both crewmembers described the airplane as shaking following the bird ingestion, the captain’s decision to begin the Engine Fire or Engine Severe Damage or Separation checklist was appropriate (one of the conditions for using the checklist was airframe vibrations). Although the crew did not report performing the Smoke, Fire or Fumes checklist, the first officer stating “masks” accomplished two of the three memory items by donning their one-piece oxygen masks. Postincident review of this checklist found that it instructed pilots to turn off various switches, including the RECIRC FAN switches at step 9. It is not until step 11 that the checklist instructs that if the smoke or fumes become the greatest threat, pilots should reference another checklist. It is likely that the incident flight crew would have performed the Smoke, Fire or Fumes checklist first if they had not experienced severe airframe vibration following the bird ingestion. Boeing released a flight crew operations manual (FCOM) bulletin on February 9, 2024, that described the results of the bird ingestion in this incident and the actions a flight crew should take if they experience a similar incident. Boeing also updated the system description in the Boeing 737-8 FCOM on November 15, 2024, and the Quick Reference Handbook (QRH) on November 30, 2024, to include engine failure with smoke or fumes in the flight deck or cabin as a condition to trigger reference to the Engine Fire or Engine Severe Damage or Separation QRC. Although the NTSB found no clear evidence of significant toxic or irritant exposure to the flight crew resulting from the LRD activation on the incident flight, such an event may pose a toxicological risk. There are insufficient data to reliably determine the nature and magnitude of such risk, especially at what is expected to be limited exposure duration. It is reasonable to consider the potential for irritant effects on the pilots among the threats to the immediate safety of the flight in an LRD-related smoke event.

Verbatim NTSB analysis and probable cause from the NTSB dataset