High Idle?

[BjornM 0]

In the video below, they do a "high idle check", and I just have to ask, what is High Idle?I have read something about High idle and Low idle (not much information), but I have no ideas what the difference is and what it means.I know very much about the 737 and have spent years flying it in Flight Simulator, I have read much about it and learned alot, but this is one of the things I do not know!

[Petr Bily 0]

Hi Bjorn,is not it like nengine test? 30%N2 should increase N2 and EGT?Petr

[scandinavian13 5,192]

There's a high idle and low idle, controlled electronically, it seems. Hi idle is used in all phases of flight, whereas low idle is used on the ground to reduce the need for braking. According to the manual, this is 4 seconds after touchdown, where it reduces from a default of approx 32% to 22%.It's mentioned in the Systems - APU & Engine manual on Smartcockpit.com;http://www.smartcockpit.com/pdf/plane/boeing/B737-classic/systems/0008/(Page 19)

[davierosoft 13]

Classic and NGs are a bit different, low idle and high idle(flight idle) only are a feature of both generations, but the NGs have also the approach idle that is higher than flight idle.The reason is simple, on ground we don't need too much speed, or mantain the speed, we need only to taxi and we don't need a fast engine spool up.But, in case of the approach, we need that idle is sufficiently high that can rapidly increase rpm in case of TOGA. when you push toga the airplane answer must be fast, and a low or flight idle will not be sufficient.The idle control will change in this mode:Classic: ground idle airplane on ground, high idle, aircraft in air condition or IDLE CONT circuit breaker pulled out (maybe in the test they used the breaker to simulate it)NG: low idle on ground, flight idle above 15500ft and whenever flaps and gears are up (cowl AI off), approach idle when eng cowl AI is used or below 15500 with flaps 15(or more) or gear down.

[Petr Bily 0]

Thank you Andrea. Sounds clear to me now.

[davierosoft 13]

;)

[Stephanovic 2]

They talk Dutch to each other, its very difficult to understand but with the high idle test he tells her N1 should be around 30% and then she says... *pause*.... "increase of 4 to 8%". Dunno if she meant N1 or N2

[davierosoft 13]

(a) With the engine at the low idle (no airbleeds or electrical loads), open the IDLE CONT circuit breaker on the circuit breaker panel, P6. (:( Make sure that the %N2 rpm increases approximately 10% and becomes stable at the target %N2 rpm.

The target N2% is dependent on some factors including OAT and baro pressure:

[ArjenVdv 190]

Just look at the N1 readout when they put in 30% N1. Look how how fast the engines stabilize. The engines of the NG (CFM56-7B) do exactly the same, but unfortunately this is not been simulated in the NGX. Instead, the spool up rate is similar to the real world, but engines take much longer to stabilize.

[BreezyPointDeparture 2]

I have never heard about this - very interesting thread

[BjornM 0]

Thanks for all the replies everyone! It's always interesting to learn something new about the 737! Again, thanks.