737NGX usually has too much power so I almost always need to derate or reduce power. Never experienced situation where I need that extra power boost with bleed air - OFF.

Excellent info. Cheers all.

737NGX usually has too much power so I almost always need to derate or reduce power. Never experienced situation where I need that extra power boost with bleed air - OFF.

if you using a short rwy and the weather is hot you need all the air you need that why the apu is left running and the bleed air switches are turned off, so all the air is used for the take off tiill your airborne

if you using a short rwy and the weather is hot you need all the air you need that why the apu is left running and the bleed air switches are turned off, so all the air is used for the take off tiill your airborne

What would you say is a short rwy for a bleeds off takeoff and what temp plus weight to do this?

Someone with performance calculator would be able to answer to that. I do not have one. I just reduce and pray :D

No word on "cold day" take-offs so far in this thread.

Engine anti-ice should be used below +10°C on the TAT display. So in case of low OAT departures engine bleed must be turned on for EAI (TAI) and later on for WAI (wing anti-ice) if humidity comes into play additionally. In case of heavy wight and steep profile DEPs on cold days with appropriate humidity a WAI vs. PACKS evaluation comes into consideration. 

 

In contrary hot day take-offs (> +24°C) demand for bleed of as this will increase performance and might avoid the "bleed air trip off" warning due to high bleed air pressure and temperature...

 

Just my thoughts about turning Engine bleeds off.

Edited June 23, 201411 yr by vr-pilot

No word on "cold day" take-offs so far in this thread.

Engine anti-ice should be used below +10°C on the TAT display. So in case of low OAT departures engine bleed must be turned on for EAI (TAI) and later on for WAI (wing anti-ice) if humidity comes into play additionally. In case of heavy wight and steep profile DEPs on cold days with appropriate humidity a WAI vs. PACKS evaluation comes into consideration. 

 

In contrary hot day take-offs (> +24°C) demand for bleed of as this will increase performance and might avoid the "bleed air trip off" warning due to high bleed air pressure and temperature...

 

Just my thoughts about turning Engine bleeds off.

TAI doesn't have to come on at +10C - only in you're in icing conditions. I think most performance tables include TAI ON if the temp is +10C or below, but that's not the same as having them on.

 

I don't think most companies account to WAI on the takeoff performance. I'm not sure, but usually if you need WAI on during the takeoff, you shouldn't be taking off. Boeing has as an option WAI on during T/O, but I think most companies have it trip off during T/O.

Yeah, something that always perplexes me about the sim crowd...

 

We grow up knowing that water freezes to make ice, but when it comes to flying, they suddenly forget water has to be part of the equation...

Yeah, but carb icing is the most a lot of simmers know, plus the charts do show TAI for +10C. I can see a couple sources for confusion.

 

Just for the discussion for everyone, I use WAI maybe 5 or 10 times a year. Pretty rare.

 

 

Just for the discussion for everyone, I use WAI maybe 5 or 10 times a year. Pretty rare.

 

I'll second that statement.  As for wing A/I on takeoff, it's our normal procedure to have it on for taxi and takeoff in icing conditions if we have not been anti-iced with type 4 fluid.  If it's on for takeoff it trips off at liftoff.

 

As far as bleeds off takeoffs about the only time we do them is when you have a transcon flight off a short runway such as DCA-LAX.  Our TPS will call for a 26K bleeds off takeoff before it will bump up to a 27K takeoff.

Just for the discussion for everyone, I use WAI maybe 5 or 10 times a year. Pretty rare.

 

 

I'll second that statement. As for wing A/I on takeoff, it's our normal procedure to have it on for taxi and takeoff in icing conditions if we have not been anti-iced with type 4 fluid. If it's on for takeoff it trips off at liftoff.

 

Very interesting. This IMO shows the actual complexity of the subject. I thought WAI on T/O would be a "no go", no matter what... :blink:

 

 

 

We grow up knowing that water freezes to make ice, but when it comes to flying, they suddenly forget water has to be part of the equation...

Well said, but TAI/EAI on below +10°C TAT on T/O is actually mandatory (AFAIK or thought), because T/O thrust fan suction will let drop the air temperature to freezing degrees and at the same time the water contained in the air will condense instantly producing an "icy" airflow . Depending on the relative air humidity this effect can be hazardous. This is in fact similar to the carburetor icing reaction. The ATIS temperature spread delivers "air humidity presence", but the rule of thumb "TAI on for TAT below +10°C on T/O" is easier to follow than fiddling with limits of temperature spreads on the emission of a new ATIS... :wacko:

 

And regarding WAI (AFAIK) it is the same for temps below +10°C TAT because of the temperature reduction caused by the low pressure over the wing profile, although here additional humidity (condensation or precipitation) is "required".

 

Greetings,

Claus

 

 

Well said, but TAI/EAI on below +10°C TAT on T/O is actually mandatory (AFAIK or thought)

 

No. Try it next time you're in the NGX and see what happens when you advance your thrust levers...

 

 

 

And regarding WAI (AFAIK) it is the same for temps below +10°C TAT because of the temperature reduction caused by the low pressure over the wing profile, although here additional humidity (condensation or precipitation) is "required".

 

Correct, but only in certain cases.  Temp-dewpoint spread within 3 degrees is at higher risk for icing.  That kind of spread, again, means there's lots of moisture in the air, which, exactly in line with my last post, is water.  Outside of that 3 degree spread?  No.

 

Anti-ice is never simply turned on because it's just cold.

 

Cold + Water.

 

Always.

Very interesting. This IMO shows the actual complexity of the subject. I thought WAI on T/O would be a "no go", no matter what... :blink:

 

 

 

Well said, but TAI/EAI on below +10°C TAT on T/O is actually mandatory (AFAIK or thought), because T/O thrust fan suction will let drop the air temperature to freezing degrees and at the same time the water contained in the air will condense instantly producing an "icy" airflow . Depending on the relative air humidity this effect can be hazardous. This is in fact similar to the carburetor icing reaction. The ATIS temperature spread delivers "air humidity presence", but the rule of thumb "TAI on for TAT below +10°C on T/O" is easier to follow than fiddling with limits of temperature spreads on the emission of a new ATIS... :wacko:

 

And regarding WAI (AFAIK) it is the same for temps below +10°C TAT because of the temperature reduction caused by the low pressure over the wing profile, although here additional humidity (condensation or precipitation) is "required".

 

Greetings,

Claus

Visible moisture AND +10C for TAI. So, you need to actually have a visibility of 1sm or less or precipitation.

 

I've seen fan blade icing and it's never been above freezing.

 

WAI is really more de-ice in that you let it build and then remove it. There isn't any issue with temp drop.

I'll second that statement.  As for wing A/I on takeoff, it's our normal procedure to have it on for taxi and takeoff in icing conditions if we have not been anti-iced with type 4 fluid.  If it's on for takeoff it trips off at liftoff.

 

As far as bleeds off takeoffs about the only time we do them is when you have a transcon flight off a short runway such as DCA-LAX.  Our TPS will call for a 26K bleeds off takeoff before it will bump up to a 27K takeoff.

What distance of runway would you say is necessary for a bleeds off takeoff?

What distance of runway would you say is necessary for a bleeds off takeoff?

 

It's a lot more complex than that:

Weight, temp, pressure, thrust setting (presumably, you wouldn't be using de-rates if you're doing a bleeds off, but that doesn't mean that you can't), wind, and runway contamination are all factors.  Programs like TOPCAT could give you more precise values.