Asiana: the facts so far
By David Learmount on July 9, 2013 4:31 The ill-fated Asiana Airlines Boeing 777-200ER had flown more than ten hours across the Pacific from Seoul, Korea, landing at San Francisco on 6 July. It carried two crews - four pilots in total - to allow periods of rest for each of them during the flight.
The flight was uneventful, and the San Francisco weather was very good when the crew began their descent toward the destination airport.
They were cleared for a visual approach to runway 28L. The crew would have known from NOTAMs (notices to airmen) before departing Seoul that
the instrument landing system (ILS) glideslope signal on runway 28L at San Francisco airport was not operational because of work to improve the runway overrun safety area, hence they should have been expecting to fly a visual approach to it.
the instrument landing system (ILS) glideslope signal on runway 28L at San Francisco airport was not operational because of work to improve the runway overrun safety area, hence they should have been expecting to fly a visual approach to it.
Runway 28L, for which they were aiming, has precision approach path indicators (PAPIs), visual devices that show red lights if the aircraft is below the ideal approach slope, white if it is above, and a mix of red and white if it is on the ideal slope.
Amateur video of the aircraft approach and crash shows that the aircraft had adopted an unusually high nose attitude during short final approach, an indication that a descending aircraft in landing configuration is flying too slowly. It was also below the ideal glideslope angle.
This contrasts with evidence suggesting that, earlier in the final approach, the aircraft had been high and fast. The autopilot is believed to have been disconnected at 1,600ft.
The National Transportation Safety Board chairman, Deborah Hersman, has confirmed that, on short final approach, the aircraft had the gear down and flaps set to 30deg, but it was flying significantly less than its target speed of 137 knots, and that the engines were at idle power. If, indeed, it was initially high on the approach a minute or two earlier, that might account for the idle power setting, but there are many variables to consider here, including whether the autothrottle was engaged at the time.
She also confirmed that one of the crew voiced concern about the low airspeed 7s before the first impact. About 4s before impact the stickshaker stall warning activated noisily, and one of the crew called for a go-around 1.5s before impact.
The engines responded to the crew's demand for power, said Hersman, but it was too late. The tail section slammed into the sea wall well short of the runway threshold, the tail and undercarriage broke off, and the rest of the aircraft bounced across the airfield surface, coming to a halt next to the runway touchdown zone, having suffered severe damage.
A fire started and spread to the fuselage. There were more than 300 people on board, about fifty were seriously injured, and two people are known to have died.
Hersman and the airline have confirmed there was no known technical problem with the aircraft, and the crew had not discussed any problems on approach.
She said that, at this stage, there is no apparent connection between this accident and the 2008 crash of a British Airways 777 that came down short of the runway at London Heathrow airport because its engines failed to respond to the pilots' demand for power. The BA accident involved ice in the fuel lines, but that was in England in January, whereas the Asiana 777 faced a temperature of 18degC on the ground, which would have made approximately the last 10,000ft of its descent in air that was above the freezing point of water.
Hersman reported that, at this stage, she cannot confirm which of the four pilots were occupying the two pilot seats during the landing, but she expects to provide that information soon. The four flightcrew included a captain under instruction, a training captain, a third captain, and the first officer.
Our Singapore-based reporter Mavis Toh has reported Asiana as saying that the pilot flying only had 43h on type, although a flying hours total of nearly 10,000h including time on 747s, so it makes sense that this was the captain under instruction. If that is confirmed, the training captain would normally - but not definitely - be occupying the right hand seat.
The Asiana crash is the first 777 accident in which there have been any fatalities.
Now follows a video in which I explain some of the issues surrounding this flight. Beware that, in the video, I incorrectly state the landing runway is 28 Right, when in fact it was 28 Left. I think that's the only error!
Ingen kommentarer:
Legg inn en kommentar
Merk: Bare medlemmer av denne bloggen kan legge inn en kommentar.