A320 Engines and Green Dot

[FLEXPWR]

Hi there, I am looking for enlighted individuals with experience on both CFM and IAE powered A320s.

I have flown with both engine configurations over the past few years, and noticed that green dot is 5 kt higher when IAE engines are fitted. Mind you, until recently, the only IAE powered A320 I operated were of the -232 variants. So for example, CFM GD at 60 tons is 200kt and IAE GD at 60 tons is 205 kt. This GD speed is calculated by the FAC during climb, (GW*2) + 80 on CFMs or +85 on IAEs, or so I presumed.

I have recently operated an A320-231. Looking at the speeds in the manuals as well as the GD in flight, the calculation is based on (GW*2) +80, just as for the CFM.

Is this normal for the A320-231 (IAE -A5 engines) or is there a documentation issue or mix up with other variants?

Thanks in advance for colleagues out there who may help with this.

[WhyByFlier]

I've only flown CFM A319/320s - with easyJet (so the A319-111 and A320-214) - on the CFMs in our fleet Green Dot is (Gross Weight X 2) + 85 for both the 319 and 320.

A BA pilot could probably help you best as I think they have many different variants across a wide range of MSNs.

[Riu]

it also depends on altitude.. usually is 1 knot for every 1000 feet above 20.000 feet of altitude.

60 tons at 10.000 feet should have 205 knots green dot
60 tons at 30000 feet should have 215 knots green dot

that is for A320, IAE or CFM.. till now, but i will have a look in the manuals next flight

[FLEXPWR]

Actually I am getting mixed up now, which is 80 and which is 85 CFM or IAE. Could be the other way around from my first post. With the new manuals update from Airbus, all docs refers to MSN rather than engine variant, so a bit more confusing.

[EDA]

I've only flown IAE engines. And FCOM states:

Below ​20 000 ft equal to 2 × weight (tons) ​+80

Above ​20 000 ft, add ​1 kt per ​1 000 ft

Don't know about CFM...

[compressor stall]

IAE and CFM A319: green Dot Speeds are identical. (Both aircraft in the late 1000s msn). Double your GW plus 85, plus the 1kt/1000ft above 20k.

[FLEXPWR]

Ok. So from EDA we have 2*GW +80 et from Compressor stall 2*GW +85.

I am not mentioning the 1kt per thousand feet above 20,000. This rule is valid in any variant.

Could there be more to it than the engines?
Is there another reason why some aircraft variants have different GD calculations? Of course I understand this in case of a 319, 318, 321, each has various weight limitations and power available.

But considering the same aircraft type (A320), is there a place I can find info about the reason for the GD calculation differences?

In the new FCOM it is written that holding speed for CFM is GD and for IAE is GD+20. Reading this kinda reinforced my belief that GD calculation difference was directly (and only?) based on engine variants.

Now I am not so sure...

Any further source welcome!

[compressor stall]

Fwiw, A319 FCOM has no difference in the holding speeds for the different engine types.

Applicability:ALL.
They are established for flight in a race track holding pattern for two different configurations: • Clean configuration at 210 kt and green dot speed • Configuration 1 at 170 kt and S speed.
Green dot speed in clean configuration and S in CONF 1 are speeds between the minimum fuel speed and the minimum drag speed.

[EDA]

Forgot to mention that it is the IAE A5 engine, so A320-232 if I am not mistaking...

[EDA]

I've found the relationship between HOLDING speed and the type of the engines, FCOM DSC 22-20-30 Flight planning / 30-10 Lateral Functions / FMS2 / Holding pattern states:

When no specific speed limit applies, the default hold speed is approximately equal to:
-Green Dot speed on the A318, A319, A320 (CFM) and A321
-Green Dot + ​20 kt for altitude lower than ​20 000 ft, on the A320 (IAE).
-Green Dot + ​5 kt for altitude bigger than ​20 000 ft, on the A320 (IAE).

[FLEXPWR]

Thanks EDA, that clarifies one aspect of it.

Now for the GD calculation, there still seems to be a bit of hesitation.

GD may be influenced by engine model/variant, but which is correct?

Flex

[flyboy007]

Perhaps the drag characteristics of the two different engine options are different, therefore giving a slightly different G.D?