A320 holding speed

[ulisse]

good day,
I found in FCOM a note tath for some MSN the holding speed for 2 engine is green dot + 20 knots, but I can't find a reason.
The MSN are fitted with IAE engine but some other MSN with the same engine are not affected.

Do you encountered this before?

thanks

[Goldenrivett]

Hi ulisse,
See post #10 by EDA: http://www.pprune.org/tech-log/518778-a320-engines-green-dot.html
"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)."

I guess GD speed is min drag on the Airbus airframe plot, but the IAE engine is more fuel efficient at +20kts for some reason.

[tubby linton]

Also discussed here:
Holding speeds with A320 IAE V2500 engine [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-523073.html)

[vilas]

I have seen a graph of CFM vs IAE where it says CFM as compared to IAE has higher thrust at higher level and lower thrust at lower altitudes. That may have some bearing on the GD.I am unable to locate the document.