Author: Steve

As the investigation of the crash of Asiana Flight 214 proceeds, it’s becoming clear that the aircraft flew an unstabilized final approach into San Francisco International Airport (KSFO). That unstabilized approach by itself did not cause the accident. However, it may have been a contributing factor, as the need to reduce power significantly due to excessive airspeed and altitude on short final masked the fact that the autothrottles had been inadvertently disengaged. By the time the crew realized that the autothrottles were disengaged and airspeed was dropping, it was too late to execute a timely go-around.

So any investigation into the accident is likely to look at airlines policies, as well as de facto practices, regarding unstabilized approaches. In this post, I compare the approaches into KSFO of two airlines (Asiana and United), and show that there are some striking differences in the way that approaches are flown by the two airlines, at least over the time span I looked at. Continue reading “Stabilized and Unstabilized Approaches at KSFO”

We all know how aircraft accidents end, with a damaged or destroyed airplane, and injured or dead crew and passengers. But how do they start? Most accidents are the result of a long chain or web of events stretching back well into the flight, or even earlier. Twenty-four years ago, United Airlines Flight 232 crashed into an Iowa corn field  due to a catastrophic engine failure, ultimately caused by a manufacturing defect in the fan disk, and the failure of maintenance procedures to detect the growing crack in the disk. That flight was destined to crash before it took off.

The chain of events stretches back from the accident itself, with one contributing cause layered on top of another. Accidents can be prevented by breaking the chain anywhere along the causal sequence. Asiana Flight 214 crashed because it approached Runway 28L too low. It was too low because earlier the airplane had slowed well below its target approach speed, and the pilots therefore could not maintain altitude. At least part of the reason it slowed below its approach speed was because the autopilot had been disengaged, and the pilots believed that the autothrottle was still engaged when it wasn’t. But why had the pilots switched off the autopilot? Perhaps in part because the approach was unstabilized, too high and too fast, and the pilots could not acquire the glide slope without hand flying the aircraft. It will be a long time before we know the full story, but one question that will have to be addressed is whether the decision not to go around was a major link in the accident chain. Continue reading “Too High, Too Fast: More Asiana Flight 214 Analysis”

At about 11:28 a.m. PDT on July 6, Asiana Airlines flight 214 crashed at the approach end of runway 28L at San Francisco International Airport (KSFO). The next day, the New York Times reported that the aircraft sank 600 feet in nine seconds (a rate of 4000 feet per minute) less that a minute and a half from impact. That’s an extraordinary sink rate, equivalent to a vertical velocity of 45.4 miles per hour. If true, that would be newsworthy. Indeed, I argued in my previous post that there was a very rapid descent at about that time, necessitated by a too fast, too high, unstabilized approach. But nothing in the data I saw suggests a 4000 fpm descent. Indeed, NTSB chairman Deborah Hersman felt compelled to deny at her July 8 briefing that AAR 214 descended at 4000 fpm. How did the New York Times reach that conclusion, and was it a plausible conclusion from the data?  Continue reading “Flight 214 and The New York Times Data Analysis Blunder”

At about 11:28 a.m. PDT on July 6, Asiana Airlines flight 214 crashed at the approach end of runway 28L at San Francisco International Airport (KSFO). Less than 24 hours after the accident, it’s way too early to know what happened, but there are some signs that the aircraft was not flying a stabilized approach at any part of the approach to land, and ended up low and slow just before impact.   Below, I outline the data that’s available at this time, and why I think that’s a possibility. But first, a disclaimer: There’s not nearly enough data to determine the cause of the accident. The below is speculation, based on the data available to me, which is not even a few percent of the data that will be available to the NTSB. Most speculation this early in the process is wrong, precisely because so little data is available. So anything below that may appear to be stated as a fact is really a conjecture. Continue reading “What Happened to Asiana Airlines Flight 214?”