Originally Posted by
BraceBrace
What are the rules for the commanded speed with or without autothrust on an Airbus?
On a Boeing, if the autothrottle is used for the landing, there is no need for wind corrections on top of the standard 5kts (all Boeings
afaik). If autothrottle is/will be switched off for landing, command speed is increased with a wind correction up to 20kts. Main wind corrections can be bled off over the runway, but gust corrections on the speed should be kept in. With the autothrottle, the system reacts aggressive if speed would drop below command speed, especially if you hit Vref, which is why the standard 5kts is sufficient.
On airbus using Auto-Thrust the approach speed is the minimum of VREF+5 or VREF+1/3 the headwind component, whichever is greater, (manual thrust is VREF or VREF+1/3 HW, this being the reason landing performance calculations are better with manual thrust in many cases). In this case, given the 28 knot headwind, the default approach speed would be VREF+9 knots. This again can be modified by the pilots up to a maximum of VREF+15, with this additional increments recommended in strong crosswinds by Airbus.
On top of this, G/S Minimum functions as well to provide a buffer if the instantaneous headwind component as computed by the IRs is greater than the tower provided headwind component, the aircraft will add the difference in headwind to the approach speed in anticipation of it being lost as the aircraft descends to the runway. In this case for example, with a VAPP of VREF+9, with the headwind on the ground of 28kts being expected, if at 500' there was a 38knot headwind, the "Fly Speed" would be VREF+19, if at 300' the headwind component was 33kts, the fly speed would be VREF+14, and so on, with the objective being that as the wind dies off the closer you get to the runway, the negative sheer is counteracted by the target speed reducing, and that you cross the threshold at the calculated VAPP (VREF+9 in this case).
All that being said, despite the extra margin being provided by G/S Mini and the VAPP increments in strong headwinds, I've always found the Auto-Thrust, both on the A330 and A320 to let you down at the worst possible moment. It can often get itself out of sync with the gusts and the speed and result in an automatic form of PIO with the thrust and can be quite slow to add power, even when the speed sinks down to or below the VLS (VREF).
Personally I've always found manual thrust the best option on both the A320 and A330 when landing in blustery conditions, it allows better anticipation of speed drops and gains and allows for local knowledge to be applied, as is often known about different airports, such as passing a certain hangar or passing by a certain ditch. It allows you to maintain current thrust setting in areas where you know a gain in airspeed will be short lived and soon die off (whereas auto-thrust would reduce thrust and then whack it back on as the speed bleeds off) or in the case of Schipol, manual thrust allows you to anticipate the drop in speed you often get in the last 40-80 feet as you descend below the tree line.
A320 Auto-Thrust performs reasonably well 90% of the time but the A330 auto-thrust in particular can often let you down for whatever reason, be it the larger engines and inertia, or just a different software gain/adjustment for counteracting airspeed reductions.
While I don't care to overly speculate, it would not surprise me that in the final report the use of auto-thrust, perhaps no additional increment being put on the VAPP due to concerns of the shorter than normal runway, the possibility of the aircraft getting low to begin with due to pilot mental perception of the shorter runway or just blustery conditions may all be listed as contributary factors.
Just worth mentioning as well though from experience, despite the shorter runway length, given the prevailing conditions, headwind, sea level, cool temperatures etc, even with a wet runway, Airbus landing performance figures from rough experience would still give you about a ~60% margin and I'd expect the calculated LDR would be in the region of 1,200m-1,300m, leaving a 700m-800m margin on the landing rollout on the 2,000m runway, and that being with proper technique (crossing threshold at 50', touchdown within touchdown zone etc.), so by no means overly limiting or close to the minimum 15% margin required.