I have seen a lot of concern regarding descents in the Airbus A350-900. Here are a couple useful tips when considering a descent from a higher altitude.
A good descent rate is 318 ft per NM. In order to find where to start descending, just take the altitude you need to lose and divide it by 318 (or 300). Say you’re descending from FL320 to 2,000 MSL, you need to lose 30,000 ft. 30,000 divided by 300 is 100. So, plan to start descending 100 NM from your point. Then, to find the rate you need to descend at, just take your ground speed and multiply it by 5. If your ground speed is 400 Knots, you need to descend at 2,000 fpm. These two rules go hand-in-hand too! In the previous example, we showed that in order to descend 30,000 ft, you need 100 NM to descend. If your ground speed is 400 Knots, you’re flying at 6.67 NM per min. So, to go 100 NM it will take 15 mins. 15 mins at 2,000 fpm is 30,000 ft! This is known as pilot math and it’s just that easy. If you find you need to descend at more than 3,000 fpm, you may need to consider slowing down to avoid overspeeding the aircraft. Using a STAR (Standard Arrival Route) can be helpful when picking altitudes as well. They can be found for most US airports online for free.
Remember: as altitude increases, true airspeed increases. So, be careful with steep descents and fast speeds at higher altitudes.
To find out when to start descending take the altitude you need to descend and divide by 300. This is the distance, from your point, in NM to start your descent.
To find out the required fpm for your descent multiply your ground speed by 5.
If the required rate of descent is above 3,000 fpm consider slowing down.