dimanche 15 décembre 2013

Trop bas, trop lent

Une vidéo de l’accident d’Asiana 214 à San Francisco :




Et un récit très précis de l’accident.
J’en retiens l’inexpérience du pilote en fonction :
A key issue I’d like to highlight is that the Captain was transitioning from a highly automated Airbus to a Boeing which allows for much more manual control by the pilot. This goes some way to explaining his confusion but does not in any way excuse why no one was watching the airspeed and why the instructor did not take control and initiate a go around much earlier.
(…)
The Pilot Flying was in the left seat. He was a captain transitioning from the Airbus 320 to the Boeing 777. He had 9,700 hours flight time with less than 45 hours in the Boeing 777.
The Pilot Monitoring was in the right seat. He was a newly certified instructor pilot with 12,000 flight hours and 3,200 hours on the Boeing 777. 
 Un autre problème : l’indicateur de descente en IFR était en panne à San Francisco au moment du crash.
L’équipage a donc effectué sa descente vers la piste sans l’aide de cet instrument mais normalement ce n’est pas gênant.
C’est, par contre, un manque d’attention à la vitesse de l’avion et une réticence de l’instructeur à reprendre la main qui semblent être à l’origine de l’accident (avec un confusion sur les indications du pilote automatique).
About 1.4 miles from from the runway and at about 500 feet altitude, the Boeing 777 descended through the normal glideslope. It passed through the desired speed of 137 knots and was now rapidly decelerating.

The Precision Approach Path Indicator (PAPI) is a visual display next to the runway which provides vertical guidance for the approach path. In a normal approach, the PAPI would show two whites and two reds. More whites means that the angle of the approach is too high. More reds than white means that the angle of the approach is too low. The PAPI shifted to three reds and one white and then to four reds.

The pitch attitude steadily increased as the pilot pulled back on the column, trying to maintain the correct glidepath as per the PAPI indicators. But with no power, it did nothing but slow the plane down even further.

There was no mention of the decaying speed on the cockpit voice recorder.

The thrust levers remained at idle. The aircraft continued to lose airspeed and sink below the glidepath.

24 seconds from impact, the airplane was .9 miles from the runway and at 300 feet altitude. It continued to descend well below the PAPI glidepath, decelerating through 120 knots and at a pitch attitude of about 7 degrees nose up.

At about 11 seconds before the impact, an audible alert consistent with low airspeed caution sounded through the cockpit.

Three seconds later, with the aircraft just below 100 feet above the water, the throttle levels were (finally) moved forward to full power to initiate a go-around. This was followed four to five seconds later by stick-shaker activation and a verbal call to go-around.

The action was too late and the main gear and underside of the aft fuselage struck the seawall. 
En résumé, le pilote ne faisait pas attention à ses commandes moteurs (parce qu’il pensait qu’elles étaient dirigées par le pilote automatique, mais celui-ci était désengagé, ce dont il ne s’était pas rendu compte), il a vu que le PAPI indiquait trois rouges, donc que l’avion était trop bas, il a voulu remonter et a cabré l’avion mais n’a pas remis de gaz ce qui a eu pour effet de ralentir l’avion encore plus (quand on relève le nez d’un avion sans mettre plus de gaz ça ralenti l’avion). La décision d’arrêter l’atterrissage et de remonter est intervenue beaucoup trop tard.

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