That Looks About Right: An Alaska Airlines Software Failure

Alaska Airlines tail strikes: While visiting Alaska – via Seattle/Tacoma International Airport – in February, I heard about two tail strikes that had just occurred, only minutes apart, on Boeing aircraft operated by Alaska Airlines, heading for Hawaii. These incidents grounded both flights and forced a temporary shutdown of Alaska’s flight activity nationwide. A tail strike occurs when the tail of an aircraft contacts the runway during take-off or landing. This can happen when the aircraft is loaded with too much weight or when the aircraft is rotated too early during take-off. Planes are designed to cope with tail strikes, and there was reportedly no major concern from these incidents, but they can pose a serious safety risk to passengers and crew in certain circumstances. A software error in the ‘critical weight’ calculation

The Seattle Times reported that the root cause was found to be a software bug in a program that holds the crucial weight and balance data in each plane’s flight computer. The critical take-off calculation takes into account several factors, including the aircraft’s weight and balance, its performance characteristics, the length and condition of the runway and the prevailing weather conditions. Specialised software programs are used to do this, and the system then provides the flight crew with an estimate of the maximum weight that the aircraft can safely carry. However, in this case the system – provided by a company called Dynamic Source – failed. The tool delivered faulty data that underestimated weights for the airplanes. This meant that the aircraft was too heavily loaded and this in turn caused the tail strikes during take-off. That looks about right… The Seattle Times reported that: …the error was enough to skew the engine thrust and speed settings. Both planes headed down the runway with less power and at lower speed than they should have. And with the jets judged lighter than they actually were, the pilots rotated too early. The bug was identified quickly in part because some flight crews noticed the weights didn’t seem right. They’re trained to be aware of the importance of accurate weight and balance calculations. During pre-flight checks the first officer reads the calculated weight data aloud and the captain verbally verifies it. Pilots routinely use an acronym when they do the pre-take-off check: TLAR, which means “That Looks About Right.” Soon after the tail strikes that day, Alaska issued a message to all of its pilots to “take a second and conduct a sanity check of the data.”

https://techsafetransport.substack.com/p/that-looks-about-right-an-alaska?utm_source=substack&utm_medium=email

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