While tail strikes happen every once in a while, two Alaska Airlines jets had tail strikes within minutes of one another, leading to all Alaska flights temporarily being grounded. The backstory here is pretty interesting, as reported by The Seattle Times.
Two Hawaii-bound Alaska 737s have tail strikes
On the morning of January 26, 2023, two Alaska Boeing 737s had tail strikes six minutes apart, while departing Seattle for Hawaii:
- At 8:48AM, a Boeing 737 MAX 9 operating flight AS801 headed for Kona (KOA) had a tail strike
- At 8:54AM, a Boeing 737-900ER operating flight AS887 headed for Honolulu (HNL) had a tail strike
In each case, the pilots felt a slight bump during takeoff, while flight attendants at the back of the cabin heard a scratching noise. The planes quickly returned to Seattle, and landed safely.
While tail strikes happen every so often, it’s rare to see them back-to-back at the same airport, on the same kinds of routes, and with similar types of planes.
At this point, Alaska’s on-duty director of operations immediately paused all takeoffs for the airline:
“At that point, two in a row like that, that’s when I said, ‘No, we’re done. That’s when I stopped things.”
Within 22 minutes, the ground stop for Alaska flights ended, as the issue was discovered. So, how could this happen?
Software bug to blame for tail strikes
Alaska Airlines uses software from a company named DynamicSource to make aircraft performance calculations. This gives pilots important details about takeoff settings, which they enter into their flight computer, to determine how much thrust the engines should use, and what the takeoff speed will be.
On this particular late January morning, a software bug in an update delivered incorrect takeoff weights. Specifically, the data showed that the planes were 20,000 to 30,000 pounds lighter than they actually were. As a result, both planes used less thrust than they should have, meaning that the planes rotated too early.
The good news is that these weren’t “close calls.” That’s because the planes still had enough runway that thrust could have been increased to get the planes off the ground with room to spare.
Furthermore, the 737-900ER and 737 MAX 9 are the longest versions of the 737 that are currently in operation, and are also most prone to tail strikes. That’s why these planes often have tail skids, which are little devices toward the lower back of the fuselage that limit the impact of a tail strike.
It was determined that of the 727 Alaska flights that day, only 30 took off with incorrect takeoff data. It was only the two Alaska flights to Hawaii that actually had serious issues, though. Presumably that’s because the planes were operated by the largest versions of the 737, and also because they were the heaviest, given the long routes they were operating.
Now, the major question is how this incorrect data didn’t raise any concerns for pilots. These planes have maximum takeoff weights of well under 200,000 pounds, so being off by up to 30,000 pounds is significant, as that’s up to 15% of the maximum takeoff weight.
You’d think these pilots would have a really good gut instinct as to what the takeoff weight should be before they get their data, and you’d think the math being off by this much would cause some manual review.
While the pilots on these two flights seemingly didn’t find anything to be suspicious, this problem was solved because other pilots contacted operations, and informed them that their numbers seemed off.
In late January, Alaska Airlines had two Boeing 737 tail strikes just minutes apart. As it was later determined, this was due to a software glitch, which calculated the planes’ weights as being up to 30,000 pounds lighter than they actually were.
This caused the pilots to apply less thrust than they actually needed, and also rotate earlier than they should have. Fortunately this glitch was quickly discovered, so other flights didn’t end up being impacted.
What do you make of this 737 tail strike incident?