I was intrigued by the plot shown at Business Insider that displays “Why Asiana Flight Crash Landed”. You can find it here. The chart obviously doesn’t really contain the full explanation for why the crash occurred, but it does do a good job of showing the data behind the loss of velocity near landing that has been described throughout the media. I was inspired to take a deeper look into the data. I used the same source at flightaware.com to get the data.
Specifically, I wanted to see if the ground speed profiles of flights using the Instrument Landing System differed from those that didn’t have that luxury. The ILS was out of service on runway 28L at SFO on July 6th. I found reports that it had been unavailable starting somewhere between June 1st and June 15th. To be safe, I compared Asiana Flight 214 landings that occurred before June 1st (with the ILS) to those that occurred after June 25th (without the ILS).
As you can see, the landings occurring before June 1st varied greatly in their velocity when approaching the runway. The flights leading up to the July 6th crash actually had a very consistent profile. The rapid loss of velocity shown in the July 6th flight is evident. The May 5th flight stands out for landing without problems at the same velocity as the July 6th flight. It does appear to have had a slower velocity throughout its approach, whereas the July 6th flight experienced rapid deceleration. Plotting the acceleration shows this directly.
Here, the July 6th flight clearly stands out.
Based only on these charts, I might guess that the Asiana Flight 214s that landed without assistance from the ILS were more consistent and safer than those that used it. But I’d be hesitant to jump to that conclusion without knowing a lot more about what goes in to landing a Boeing 777. I look forward to the NTSB’s final report about what events led to this incident. In the meantime, it sure was fun to play with this little bit of data that’s publicly available.
Edit: Business Insider picked up my post here! I think this is a good point for us to stop linking back and forth.