What happened
On June 26, 1987, at approximately 15:45 Central Daylight Time, United Airlines Flight 99, a McDonnell Douglas DC-10 (registration N13238), was preparing for takeoff from runway 26C at William P. Hobby Airport in Houston, Texas. Simultaneously, two USAir flights, Flight 25 and Flight 199, both Boeing 737s, were also taxiing for departure.
Due to operational delays, the crew of USAir Flight 199 shut down their number two engine in accordance with fuel conservation procedures. Shortly after United Flight 99 received clearance for takeoff, the crew of Flight 199 restarted their engine. This action caused a momentary flameout and emission of flames from the tail cone area.
The captain of USAir Flight 25 observed these flames and transmitted a warning on the tower frequency: "99, you're right engine's on fire." At that exact moment, United Flight 99 was lifting off. The captain of United Flight 99, interpreting the transmission as accurate, decided to abort the takeoff above V1/VR speeds rather than continuing into low ceiling conditions with fog and rain.
The crew attempted to stop on the hard surface but was unable to do so before leaving the runway. The aircraft came to rest on muddy terrain adjacent to the runway. One passenger sustained minor injuries during the evacuation process.
The investigation
Investigation revealed that the tower controller was unable to see the runway due to low visibility conditions, which were reported at 3/8 mile. The controller could not verify the status of United Flight 99's engines or confirm the nature of the flames observed by USAir Flight 25.
The investigation confirmed that the flames seen by USAir Flight 25 originated from its own number two engine during restart, not from United Flight 99. The miscommunication and lack of visual confirmation by air traffic control contributed to the confusion.
Findings
The primary factors leading to this incident were:
- Misinterpretation of a radio transmission regarding an engine fire on a different aircraft.
- Lack of visual confirmation by air traffic control due to poor weather conditions.
- Decision to abort takeoff above V1/VR speeds, which exceeded the available stopping distance on the runway.
The investigation highlighted the critical importance of clear communication and verification in high-stress situations. The incident underscored the risks associated with aborted takeoffs at high speeds, particularly when visual cues are unreliable.
Safety message
Aviation safety professionals emphasize the need for precise communication during critical phases of flight. Pilots must verify information from multiple sources before making decisions that affect aircraft performance and safety. Air traffic control plays a vital role in providing accurate situational awareness, especially in low visibility conditions.