**Update: 19/09/21 @ 13:00 UTC – Statement provided by United Airlines. This has been included in the article.**
Sometime on September 17th, a United Airlines Boeing 737-900 tipped backward, experiencing a stationary tail strike. Having arrived in Lewiston (Idaho) after a flight from LAX, the aircraft was photographed in its unfortunate position, with the picture then being shared on Twitter.
What we know so far
Not many details have come out regarding this incident. However, we do know that the aircraft involved was a United Airlines Boeing 737-900ER that had landed in Lewiston  (LWS) after operating flight UA2509 from LAX.
A photo posted by JACDEC on Twitter (embedded below) shows the aircraft tipped backwards onto its tail/rear fuselage. Near the middle-front area of the 737, airport crews can be seen surrounding it. In the foreground, a baggage tractor can be seen parked, with a couple of 'onlookers' spotted even closer to the camera. Data from Planespotters.net states that the incident occurred during disembarking.
The 737 had landed in Lewiston at 17:13 local time, according to data from RadarBox.com, and is registered as N78448. Delivered in March of 2012, this particular aircraft is a nearly 10-year-old Boeing 737-900ER configured with two classes: 20 seats in business and 159 in economy.
No injuries have been reported at this time.
How could this have happened?
Simple Flying had inquired with United Airlines regarding the details of this incident. Responding to our inquiry, the airline issued the following statement:
"United flight 2509 flying from Los Angeles, California to Lewiston, Idaho landed without incident. Due to a shift in weight and balance during the offloading process, the tail of the aircraft tipped backward. No injuries were reported among our customers, crew or ground personnel. The return flight was on a different aircraft as originally planned."
As confirmed by the airline, this incident was caused by an imbalance of weight, which took place during disembarkation.
If we assume that passengers disembarked only from the front door of the 737, we can imagine that the aircraft would be increasingly 'tail heavy' as people stepped off the aircraft in a front-to-back disembarkation procedure.
With a loaded baggage cart positioned in front of the aircraft in the photo, we can infer that even more of the aircraft's front weight was removed. Indeed, the offloading of baggage from the aircraft's front cargo hold would only serve to further exaggerate the imbalance between the front and rear of the jet.
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Did someone forget the tail stand?
Another factor would have been the absence of a tail stand, which is used to "prop up" or reinforce the aircraft's tail during the loading and unloading of cargo. Those commenting on the Twitter post note that this important piece of equipment was either forgotten or not provided by the airline and unavailable at the airport.
Not all aircraft require a tail stand. However, it's been noted by some that the Boeing 737-900, in particular, is rather tail heavy and has a higher risk of tipping. As a result, it would be one aircraft type using a tail stand more often than other jets.
What do you think of this incident? Did you know about the 737-900's weight and balance characteristics? Let us know what you think by leaving a comment.