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TheMessenger
29th Mar 2010, 06:43
Why do some carriers with GE engines do a 30 second run up for anti ice on and some do not? Is it really a GE requirement?

Bullethead
29th Mar 2010, 06:53
Is it really a GE requirement?

Yep, with the CF6 engines on the plane I fly, if the OAT is 3degC or below run up to 60% N1 for approx 30seconds to confirm stable operation.

Same plane but with RB211's,

Run up to 60% N1 for 10 secs to confirm stable operation.

There is also a periodical run up requirement for each type of engine for ground operations in extended icing conditions.

Regards,
BH.

captjns
29th Mar 2010, 07:54
Not limited to GE motors... same procedure but different RPMs for the Pratts too.

SNS3Guppy
29th Mar 2010, 08:30
Our policy on the JT9D's was recently changed to a brief run of an unspecified duration, above 50% N1. It used to be 15 seconds.

Tinwacker
29th Mar 2010, 09:33
TheMessenger:

As per the previous posts to ensure no icing before a performance run evaluation in low temps with high visable moisture content.

The high power engine run will usually be calculated with 'No bleeds ON', hence checking icing with approx 30 sec anti-ice valve operation before hand.

TW

lomapaseo
29th Mar 2010, 14:05
Not limited to GE motors... same procedure but different RPMs for the Pratts too.

I sure hope the RPM on the ground is not different.

The orignial posters question did not clarify when the run-up was to be performed (in the air or on the ground)


Ground opereations are quite different and more prone to create engine ice because the idle RPM is much lower than flight idle and/or the engine sucks air and depresses the temperature compared to the outside air temp. The idea behind the runups is to blow the ice loose on the core entrances before it gets big enough to cause blading damage. Hence the timing of the runups.

The N1 RPM is extremely important since it takes windage from the fan to do the job. Since all big fan engines are similar the 60% number should be constant across the fleets. The recommendations (read your manuals) were intended to be similar to avoid confusion and ole wifs tales among the pilots. Thus the wording should be very similar among the various manuals. If they ain't then confusion is going be there.

For some engines, fan blade icing may occur either on the ground or in the air. Again the idea is to shed the ice before it gets big enough to cause pilot distractions or downstream damage. However it's centrifugal speed that does the trick so some (engine specific variations may be found.

TheMessenger
29th Mar 2010, 14:38
I asked this question because when the conditions exist (<10C + visible moisture) that require us to do a 30 second runup at 60% N1 on the runway prior to the takeoff run, I see NO other carrier doing it.

This 30 second runup can cause MAJOR delays at busy airports like Chicago.

My point is that I observe NO other carrier doing these required runups prior to their takeoff roll.

rogerg
29th Mar 2010, 15:44
The 30 sec "run up" can often be done as part of the setting T/O power on non limiting runways. You just wind the power on slowly, so providing the 30secs before setting T/O pwr. To someone not on the flt/deck it could look like the 30secs requirement has been ignored.

Cough
29th Mar 2010, 16:16
Not forgetting the runup may be started prior to receiving the t/o clearance. Ie. Heavy departs ahead, you wait 1m30 and then start your runup in anticipation of receiving t/o clearance after 2 min...

nnc0
29th Mar 2010, 16:54
Other NA carriers are doing it (and we learned the hard way - with good reason)

Tinwacker
29th Mar 2010, 17:32
TheMesenger:

Sorry I got sidetracked as at the time it wasn't clear that your runups were just prior to the takeoff roll.

I was in fact conducting something similar but prior to an engine performance high power run 'On the Ground'.

The orignial posters question did not clarify when the run-up was to be performed (in the air or on the ground)

For my case I will speak to the man on the headset.....

TW

SNS3Guppy
30th Mar 2010, 07:40
Our runs prior to takeoff are done on the runway, now have an unspecified period, and only require that the motor reach 50% N1. It is not a matter of slinging ice, but of creating enough heat for nacelle anti-ice.