A330 Descent Calculation Rule of Thumb

[cabbages]

On the minibus Ive found 3x height in thousands of feet plus 6 as a good approximation for distance required in nms for descent planning.

Now im converting onto the A330 has anyone got any useful rules of fun for descent planning

thanks

cabbage

[LukeEGTE]

Don't you just go down when you reach the little descent arrow on the nav display? :confused: :}

[MestiAdaSaudara]

I agree with Luke, go down with the arrow but if you really want to use the noggin, I use htX4, some people use htX3+20 at high alt and htX3+15 below FL250. FM is more conservative, greater than htX4. The FM doesn't seem to like doing DECEL during decent. It normally plans DECEL quite far out at an intermediate STAR level off point.

Have fun.

MAS

[cabbages]

thanks mas

that was the kind of stuff i was after.

luke - yes managed ToD is great until youre put on a radar hdg and given an unfamiliar shortcut at an unfamiliar destination - then id like a little bit more info than the range ring when planning my descent point and speeds.

[Bearcat]

cabbages, just get used to the aircraft....like us all you'll learn as you gain experience.....it took me a full year to feel comfortable with the machine......the one thing you dont want to do is over cook the descent and dropping the gear should get you out of most tight situatons..

[Capt Fathom]

If you are given an unfamilar shortcut, you won't know the track miles anyway! It's all just a guess.

[FlexibleResponse]

Ok, I’m a sucker so here goes.

A guide to monitor descent profile that has served me well:

Use of FM descent is recommended until below 10,000’. As always, be careful when entering alt constraints on the descent path. Incorrect use of the “at”, “at or above” or “at or below” functions may give you a totally unexpected too-early or too-late descent point!

130-165nms =A general check of FM Descent point from high alt crz which is normally in this range.

85-105nms = F200 @ 300kts.

During descent, be careful with any reduction in actual speed below FM speed, as this will cause you to go high on profile. Fix any high profile deviation with immediate use of speedbrake (you have been warned!) unless an increase in track miles by ATC is expected.

30nms = 7000’AAL @ 250kts Clean. Use the vertical modes to achieve this point if the FM doesn’t. This is a personal target gate recommended to me by my Airbus trainer in Toulouse.

Decel to Green Dot between 7000 and 4000’AAL depending on the terrain, GS intercept point and ATC requirements.

Approaching ILS GS select Flap 1 and intercept GS from below at less than 196kts.

At ILS GS intercept, select Flap 2 to prevent speed from increasing above Flap 2 speed.

In the case of intercept of ILS GS above about 4000-5000’AAL (e.g., KIX ILS 06), Flap 2 and some speedbrake (or gear down) may be required to prevent IAS from exceeding Flap 2 limit speed.

[ahmedette]

This applies to the 330 - 200. Don't know how much different the 330 - 300 is.

Look at your ground speed over 10 and subtract 15. To that add 3 times the altitude in thousands.

This provides a dynamic and reasonably accurate check on an uninterrupted (ie ATC modified) descent profile from TOD to around 5000 ft, before configuring for landing.

Example. GS 480, FL 380.

480/10 - 15 = 33.
3 x 38 = 114.

Distance = 33 + 114 = 147 NM.

Performing this calculation frequently on descent should confirm the accuracy. :D

[Iakklat]

I would use a three times profile and then buffer it by allowing a decel phase of taking 1 mile to lose 10kts of airspeed.So 300kts to say 210 kts i would allow 9 miles of decceleration.Obviously varied slightly with weight and wind as well,but rough rule of thumb worked for me on the A330 300.

[MasterBates]

In case of a shortcut, does Airbus have an "offpath descent circle" like the Pegasus FMC in the 757/767?
That´s really quite a neat feature.

[flash8]

OFFPATH DES also on 744 if I recall (all Boeing Honeywell FMC's?) - displays clean and speed brake energy circles on the map - neat feature for sure

[javelin]

The 330 does carry energy well, you have to plan well, put accurate descent winds and appropriate speeds in, make all level off's conditional - at or above, at or below, if you are in a Trent powered one, allow a little for anti ice, if you want to save some gas, drop the cabin descent rate to 250' per minute, that starts you down sooner but saves a couple of hundred kee's of gas. Once you have finished fannying around with vectors, clear the box to an inbound radial, use the level off arrows, let the force be with you !

My best - Miami radar GTK head went down, we were left high into POP. Started down from 390 at 75n.m. track - entered downwind at POP, 210kts, level 1500' - awesome beast, 8900 f.p.m. Asked the back end if they noticed anything - no came the reply ;)

[FlexibleResponse]

if you want to save some gas, drop the cabin descent rate to 250' per minute, that starts you down sooner but saves a couple of hundred kee's of gas.jav,
Be careful of the little white lies that the FM tells. I think you will agree that basic jet engine performance theory tells us that an early descent will cost more fuel?

Sporty Miami descent!

[jtr]

8900 f.p.m.

Sustained.....
or accelerating, with speedbrake, in a turn???

[tired]

Iakklat's method works well on the 340, too! I use a gate of 10 miles, 3000', 200kts and aim at that.

Don't know about the 330, never flown them, but I'm not too enamoured of the 340's vertical nav. Usually starts you down far too early, then eases off the ROD too much and ends up diving at the 1st constraint - usually missing it too unless the pilot intervenes. Technology, eh.....!

Which goes to prove - don't get too immersed in the automatics, just fly the bloody thing. :) ;)