Apparently the Airbus move rather quickly, have lots of inertia, and are designed to be as slippery as a fish so they're rubbish at slowing down; welcome to operations on a short haul jet!
As we worked through the earlier exercises, expectations were increasing, and the ability to handle the aircraft with a decent level of competence was required. As the Airbus is capable of higher level cruise, we now need to think about how this effects our operation, and how to plan accordingly to satisfy any speed or level constraints. Up to now descents have been from a few thousand feet, and if the aircraft was higher than planned shoving the nose down would more than compensate. Unfortunately doing this in a jet will cause it to accelerate, and because it is so much heavier it carries a greater inertia, inertia which means slowing down takes quite a few miles. Therefore one of aviations famous rules of thumb comes into play!
In the case of descent planning, a good start point is work out how many thousands of feet you need to lose, then multiply that number by three to get your average track miles. As an example starting from 30,000 feet and descending to the Willo hold at Gatwick (say 10,000ft), you want to start descending at a range of 60 track miles (20 x 3). In addition, the aircraft will be flying faster at a high level (~300kts/345mph), but if it arrives at the hold at the speed it will go steaming through and out the other side. With this in mind a good target speed is known as 'green dot' (~210kts) which is the lowest speed the aircraft wants to fly at without any lift devices deployed on the wing, so at some point a deceleration of 90kts needs to happen. With the slippery characteristics of a jet another rule of thumb is that the deceleration will take about 1 mile per 10kts speed reduction, so from our cruising level of 30,000ft and at a speed of 300kts, we really want to initiate the descent some 70 miles from the hold to arrive at the right level and speed. There are other factors to consider such as tailwinds, or ATC slowing the aircraft down earlier (jets are poor at going down and slowing down at the same time), but you get the general idea!
Before the descent even commences the aircraft needs to be prepped, passengers put back in their seats, and the pilots need to brief the approach, so if all this hasn't started by the 100 miles to go mark, chances are there will be a lot of catching up to do. This is a lesson we are gradually learning, and as much as the early details are fairly relaxed (relaxed compared to whats coming later), getting into good habits now will pay dividends later in the course. So for the moment I will continue taking baby steps, and as the workload ramps up hopefully my capacity does too! Sorry for the lack of pics, dashing to a sim now so will hopefully have some later.
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