Anti ice usage and N1%

[Stearmandriver 2,271]

My source does use the NGX and flys the real NG and says The N1 increase from using Anti-Ice is negligible and has no noticeable impact on your descent rate.

That's... ridiculous, Vernon. Your source may need to reevaluate. Engine anti-ice has a very noticeable impact on descent rate. Why do you think there's an entry on the Descent Forecasts page to tell the box when you plan to use it? So the box can take that into account when calculating descent.

 

I haven't quite been flying 73s for 15 years (but certainly long enough to be familiar with A/I in descents) but I've been flying jets for longer than that. This is pretty standard stuff.

[Guest]

My source does use the NGX and flys the real NG and says The N1 increase from using Anti-Ice is negligible and has no noticeable impact on your descent rate.

Hi Vernon,

 

In response to your PM you asked if using anti-ice during final approach would increase your ROD with which I replied "The N1 increase from using Anti-Ice is negligible and has no noticeable impact on your descent rate"

 

Back to basics.... When you select the engine anti-ice on bleed air is taken from the engine to heat the engine cowling, the EEC selects "Approach Idle" which is what gives a slight increase in N1/N2 etc.

 

Now without firing the sim I don't know how accurately this is simulated. I’ve been flying the -800 for 4 years and I still couldn’t tell you how much N1 increases in real life, I just know it does for above said reason! In response to your post I think it’s a little unwise to claim the N1% is over exaggerated, I’m flying tomorrow and I’ll tell you exactly how much it increases by so you can compare it yourself!

 

That's... ridiculous, Vernon. Your source may need to reevaluate. Engine anti-ice has a very noticeable impact on descent rate. Why do you think there's an entry on the Descent Forecasts page to tell the box when you plan to use it? So the box can take that into account when calculating descent

 

To be fair I've never used or have ever flown with a Captain who has used TAI FCST due to the unpredictably of turning it on and off during a typical descent in Europe through all the gnarly weather and I've never considered how this will affect my descent profile. It does make a small difference to your descent of course but as you know from your experience, it makes very little difference to your planned profile compared to say a speed change from ATC or a massive shortcut!!

[Stearmandriver 2,271]

Agreed in the sense that I rarely plug it in the box unless it seems likely to be on all the way down, which definitely happens some of the places we fly in the winter. But in my experience, using TAI for more than a few minutes = speed brake or increase in descent speed to stay on path. I don't know what the actual N1 increase is, I've never really paid attention to that, I don't guess it's more than a percent or two, and I also don't know what the ngx sim does... but in terms of descent rate, it's definitely enough to have a notable impact. Every jet I've flown has behaved that way.

[Bobsk8 12,678]

I love when someone that has most likely never flown a plane in real life starts telling professional pilots how it should be... 

[Guest]

Probably the case on other jets! The problem is there are too many other variables thrown in which have a far bigger impact to your descent rate then the use of TAI. I can certainly remember using TAI recently pretty much from TOD all the way to approach, we didn't pre-populate the DES page with TAI information and all the way down VNAV did a sterling job keeping the aircraft on it's descent profile and speed.

[Stearmandriver 2,271]

The Embraer family was definitely impacted worse, with the 145 being the very worst, particularly with the restrictions on flap usage in icing conditions that that particular airline imposed for the first few years I was there... but I've never seen a jet not be affected like this.

 

I have a feeling we're agreeing, just using different interpretations of what's significant. Sure other factors like a speed assignment, shortcut or wind change can have a bigger effect, and we all know what a stellar job the 73 box does with VNAV planning anyway ;-). But watch next time you turn it on in smooth air... bet you'll see a couple hundred fpm descent rate change.

[Jet Tech 31]

I look forward to your support ticket.

[NJ_Flyer 3]

[ALF1 15]

Speaking of Anti Ice, if you need to climb through the 20's using engine and wing anti ice, how much would this bog down your climb rate ?

[downscc 1,327]

Speaking of Anti Ice, if you need to climb through the 20's using engine and wing anti ice, how much would this bog down your climb rate ?

It would be measurable but definitely not as bad as "bogging" you down.  Keep in mind that the only reason for the increase N1 during descent is to keep the bleed manifold pressurized; during climb power, this is never going to be a problem.  It's not a matter of flow and much as it is pressure, although the two are related engineers are usually looking at only one or the other as a constraint.

[ALF1 15]

Thanks Dan.

[Stearmandriver 2,271]

Yeah, again, it's probably only a couple hundred feet per minute. By the time you got high enough to start sweating climb performance, it would have long since gotten cold enough to turn the anti ice off.

[Spin737 102]

I flew turboprops for about 10 years. On the SAAB 340, we called engine anti-ice "Climb Inhibitors."

 

On the 737, your not struggling for climb performance most of the time, and if you are, it's near the cruise limits. You shouldn't need anti-ice up that high.

[joolsd 10]

Has it been reported that the N1% is over exagurated when using anti ice? Before i submit a ticket...

 

The only way for a layman to verify this is to hirer out a professional L-D simulator. Then you have an interpretation, other than a professionals  A bit of an expensive experiment, however.

 

I have been caught out by this (N1) phenomena in the past, over exagurated or not I certainly found out about it. Even with P3D, you feel some things have to be over exagurated.

[downscc 1,327]

 

 

Even with P3D, you feel some things have to be over exagurated.

 

I have thought about this over the years and my conclusion is that there is always a perception dissonance between simulation and reality. Current Level D's are quite good compared to the Link C-141 Starlifter that was my first experience and orders of magnitude above PC-based simulation; regardless, one always senses differences that may be real or just perceived. Acceleration, vibration, sounds, smells etc., can be simulated but only to a degree.  Ever notice the difference between vinyl and CDs, or transistor and tube? Real or perceived... I don't know.

 

Sorry, I digress.